[PATCH v6 00/19] selftests/mm: improve khugepaged coverage

[PATCH v6 00/19] selftests/mm: improve khugepaged coverage

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

khugepaged collapses to mTHP orders since 7.2, and 7.3 added three
selftest cases for it: the generic collapse cases run at one order named
by -c, with the result detected by counting folios of that order.

That leaves the collapse path largely untested.  The suite does not run
where a PMD is 512M.  A folio count cannot say where a collapse landed.
Fixed sleeps cannot tell "not collapsed" from "not scanned yet".  And
nothing exercises collapse under contention.

Close those gaps in order:

 - Make the suite run at a 512M PMD: scale the collapse wait with the PMD
   size, skip what such a PMD cannot serve, make the swapout the swap
   cases depend on deterministic, and keep khugepaged out of the
   MADV_COLLAPSE cases.

 - Detect results per window rather than by count, with folio-order
   helpers in vm_util that are checked against the kernel before any
   collapse test trusts them.

 - Drive khugepaged deterministically: a completion barrier that wakes the
   daemon and waits for a full pass, and a check that one pass yields one
   attributed collapse.

 - Cover collapse at every supported order by default: which window
   collapses, occupancy at both limits, sources that are already large
   folios, and a fork-shared source under concurrent writes.

 - Race collapse against everything that can touch its sources, at both
   occupancy limits and over whole-table zaps, checked by content and by
   the kernel's own assertions.

Everything passes on an unmodified kernel.

Changes since v5:

 - Rebased onto mm-new: hugepage_settings lives in tools/lib/mm now, so
   the new helpers and the three new binaries follow it there.
 - The MADV_COLLAPSE cases set the per-order controls to "never" rather
   than "inherit", which "mm: shmem: ignore sysfs configs for shmem
   forced collapse" (in mm-new) made safe for shmem, and the Fixes tag
   names the khugepaged commit that started the interference (Baolin
   Wang).
 - The "-c at or below -s" check moves from patch 14 to patch 12, where
   -s first gains that meaning (Baolin Wang).
 - Patch 08's changelog no longer claims check_huge_anon() reads smaps
   (Baolin Wang).
 - The two Sashiko fixups posted against v5 are folded in: the fork race
   closes its pipe and checks waitpid(), and the race harness keeps its
   mremap scratch address reserved.
 - Baolin Wang's Reviewed-by on 01-05, 07, 10 and 14, Tested-by on 14.

Merging is_range_backed_by_order() with the check_huge_*() family stays a
follow-up, once Yeoreum's rewrite of those on top of pagemap and
kpageflags has landed.

Tested on mm-new 498ee28e5ec4 with KASAN, lockdep, DEBUG_VM and
page_table_check, in 16G guests:

  x86-64/4K   khugepaged all:all  104 pass, 11 skip, 0 fail
  arm64/64K   khugepaged all:all  102 pass,  3 skip, 0 fail

folio_order_check, khugepaged_sync_check and khugepaged_race pass on both.

The skips are structural: tmpfs cannot host some file cases, and mixed
sources has no order below the smallest.  arm64 never registers the file
and shmem contexts, having no PMD-order page cache folio.

Range-diff against v5:

 1:  759b73a5f738 !  1:  14a0a1d44862 selftests/mm: raise the khugepaged test-case cap
    @@ Commit message
         Acked-by: Usama Arif <usama.arif@linux.dev>
         Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
         Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
    +    Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
         Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
     
      ## tools/testing/selftests/mm/khugepaged.c ##
 2:  8160b5446e94 !  2:  2265f32a677c selftests/mm: skip collapse_compound_extreme() where the PMD is too large
    @@ Commit message
         Assisted-by: LLM
         Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
         Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
    +    Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
         Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
         Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
     
 3:  c6a21ef8d798 !  3:  f14ae037a749 selftests/mm: scale khugepaged's collapse wait with the PMD size
    @@ Commit message
         Assisted-by: LLM
         Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
         Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
    +    Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
         Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
         Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
     
 4:  b039045f38b3 !  4:  cbe5dac4febc selftests/mm: skip khugepaged page cache cases without a PMD folio
    @@ Commit message
     
         Assisted-by: LLM
         Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
    +    Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
         Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
         Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
     
    - ## tools/testing/selftests/mm/hugepage_settings.h ##
    -@@ tools/testing/selftests/mm/hugepage_settings.h: void thp_set_read_ahead_path(char *path);
    + ## tools/lib/mm/hugepage_settings.h ##
    +@@ tools/lib/mm/hugepage_settings.h: void thp_set_read_ahead_path(char *path);
      unsigned long thp_supported_orders(void);
      unsigned long thp_shmem_supported_orders(void);
      
 5:  0ee82084bd2b !  5:  021a1fcf711a selftests/mm: make the swap cases' swapout reliable
    @@ Commit message
     
         Assisted-by: LLM
         Reviewed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
    +    Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
         Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
         Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
     
 6:  4e48b431671e !  6:  e80ef0e8acc0 selftests/mm: stop khugepaged during the MADV_COLLAPSE cases
    @@ Commit message
         collapses the very range the case is working on, and the case fails on a
         collapse that was interfered with rather than refused.
     
    -    Clear the per-order controls too, setting them to "inherit" rather than
    -    "never": khugepaged honours the global never and stays out, while
    -    MADV_COLLAPSE on shmem still finds an order to build.
    +    Clear the per-order controls too.  MADV_COLLAPSE does not consult them:
    +    anon never did, and shmem stopped with "mm: shmem: ignore sysfs configs
    +    for shmem forced collapse".
     
    -    Fixes: 9f0704eae8a4 ("selftests/mm/khugepaged: enlighten for multi-size THP")
    +    Fixes: b7f16963efe7 ("mm/khugepaged: run khugepaged for all orders")
         Assisted-by: LLM
         Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
     
    @@ tools/testing/selftests/mm/khugepaged.c: static bool is_anon(struct mem_ops *ops
      	ksft_print_msg("%s...", msg);
      
     @@ tools/testing/selftests/mm/khugepaged.c: static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
    - 	/*
    - 	 * Prevent khugepaged interference and tests that MADV_COLLAPSE
    - 	 * ignores /sys/kernel/mm/transparent_hugepage/enabled
    -+	 *
    -+	 * "inherit" rather than "never" so that MADV_COLLAPSE on shmem still
    -+	 * finds an order to build.
      	 */
      	settings.thp_enabled = THP_NEVER;
      	settings.shmem_enabled = SHMEM_NEVER;
     +	for (i = 0; i < NR_ORDERS; i++) {
    -+		settings.hugepages[i].enabled = THP_INHERIT;
    -+		settings.shmem_hugepages[i].enabled = SHMEM_INHERIT;
    ++		settings.hugepages[i].enabled = THP_NEVER;
    ++		settings.shmem_hugepages[i].enabled = SHMEM_NEVER;
     +	}
      	thp_push_settings(&settings);
      
 7:  154a014dc5ad !  7:  e61798d22782 selftests/mm: move is_backed_by_folio() into vm_util
    @@ Commit message
         Assisted-by: LLM
         Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
         Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
    +    Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
         Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
         Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
     
    @@ tools/testing/selftests/mm/split_huge_page_test.c: const char *kpageflags_proc =
     -	return (pfn_flags & folio_tail_flags) != folio_tail_flags;
     -fail:
     -	ksft_exit_fail_msg("Failed to get folio info\n");
    --	return false;
     -}
     -
      static int check_after_split_folio_orders(char *vaddr_start, size_t len,
    @@ tools/testing/selftests/mm/vm_util.c: int pageflags_get(unsigned long pfn, int k
     +	return (pfn_flags & folio_tail_flags) != folio_tail_flags;
     +fail:
     +	ksft_exit_fail_msg("Failed to get folio info\n");
    -+	return false;
     +}
     +
      /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
 8:  a23eab162641 !  8:  be5fb9342657 selftests/mm: add folio-order check for address ranges
    @@ Commit message
     
         An mTHP collapse test needs to know that a range is backed by folios of the
         target order, and that they sit where a collapse would put them.  Nothing
    -    answers that today: is_backed_by_folio() classifies the folio behind a
    -    single page, and check_huge_anon() reads smaps AnonHugePages, which only
    -    accounts PMD mappings.
    +    answers both: is_backed_by_folio() classifies the folio behind a single
    +    page, and check_huge_anon() counts the folios of an order in a range
    +    without saying where they start.
     
         Add is_range_backed_by_order().  It requires every folio-sized, folio-
         aligned part of the range to map one folio of that order, head to tail,
    @@ Commit message
     
      ## tools/testing/selftests/mm/vm_util.c ##
     @@ tools/testing/selftests/mm/vm_util.c: bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
    - 	return false;
    + 	ksft_exit_fail_msg("Failed to get folio info\n");
      }
      
     +/**
 9:  cd741198f81e !  9:  af0191f5548c selftests/mm: add folio-order detection self-check
    @@ tools/testing/selftests/mm/Makefile: TEST_GEN_FILES += guard-regions
      TEST_GEN_FILES += rmap
      TEST_GEN_FILES += folio_split_race_test
     +TEST_GEN_FILES += folio_order_check
    - 
    - ifneq ($(ARCH),arm64)
      TEST_GEN_FILES += soft-dirty
    + 
    + ifeq ($(ARCH),x86_64)
     
      ## tools/testing/selftests/mm/folio_order_check.c (new) ##
     @@
    @@ tools/testing/selftests/mm/folio_order_check.c (new)
     +
     +#include "kselftest.h"
     +#include "vm_util.h"
    -+#include "hugepage_settings.h"
    ++#include <mm/hugepage_settings.h>
     +
     +static int pagemap_fd;
     +static int kpageflags_fd;
    @@ tools/testing/selftests/mm/run_vmtests.sh: CATEGORY="pfnmap" run_test ./pfnmap
     
      ## tools/testing/selftests/mm/vm_util.h ##
     @@
    - #include <linux/fs.h>
    + #include <mm/hugepage_settings.h>
      
      #define BIT_ULL(nr)                   (1ULL << (nr))
     +#define ALIGN(x, a)                   (((x) + (a) - 1) & ~((a) - 1))
10:  2099301ff2c1 ! 10:  a105628f6e9b selftests/mm: add khugepaged completion barrier helper
    @@ Commit message
         khugepaged knob only when its value changes.
     
         Assisted-by: LLM
    +    Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
         Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
         Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
     
    - ## tools/testing/selftests/mm/hugepage_settings.c ##
    -@@ tools/testing/selftests/mm/hugepage_settings.c: void thp_read_settings(struct thp_settings *settings)
    + ## tools/lib/mm/hugepage_settings.c ##
    +@@ tools/lib/mm/hugepage_settings.c: void thp_read_settings(struct thp_settings *settings)
      	}
      }
      
    @@ tools/testing/selftests/mm/hugepage_settings.c: void thp_read_settings(struct th
      void thp_write_settings(struct thp_settings *settings)
      {
      	struct khugepaged_settings *khugepaged = &settings->khugepaged;
    -@@ tools/testing/selftests/mm/hugepage_settings.c: void thp_write_settings(struct thp_settings *settings)
    +@@ tools/lib/mm/hugepage_settings.c: void thp_write_settings(struct thp_settings *settings)
      			shmem_enabled_strings[settings->shmem_enabled]);
      	thp_write_num("use_zero_page", settings->use_zero_page);
      
    @@ tools/testing/selftests/mm/hugepage_settings.c: void thp_write_settings(struct t
     +	thp_update_num("khugepaged/max_ptes_shared", khugepaged->max_ptes_shared);
     +	thp_update_num("khugepaged/pages_to_scan", khugepaged->pages_to_scan);
      
    - 	if (dev_queue_read_ahead_path[0])
    - 		write_num(dev_queue_read_ahead_path, settings->read_ahead_kb);
    -@@ tools/testing/selftests/mm/hugepage_settings.c: void thp_write_settings(struct thp_settings *settings)
    + 	if (dev_queue_read_ahead_path[0]) {
    + 		int ret = write_num(dev_queue_read_ahead_path,
    +@@ tools/lib/mm/hugepage_settings.c: void thp_write_settings(struct thp_settings *settings)
      	}
      }
      
    @@ tools/testing/selftests/mm/hugepage_settings.c: void thp_write_settings(struct t
      {
      	if (!settings_index) {
     
    - ## tools/testing/selftests/mm/hugepage_settings.h ##
    -@@ tools/testing/selftests/mm/hugepage_settings.h: static inline void thp_save_settings(void)
    + ## tools/lib/mm/hugepage_settings.h ##
    +@@ tools/lib/mm/hugepage_settings.h: static inline void thp_save_settings(void)
      	hugepage_save_settings(/* thp = */ true, /* hugetlb = */ false);
      }
      
11:  060448cb8a03 = 11:  27295f7decd1 selftests/mm: add order-parameterized khugepaged collapse cases
12:  674fbf72a481 ! 12:  60e86026c227 selftests/mm: parameterize the mixed-source collapse case by source order
    @@ Commit message
         supported mTHP order below the target.  The other mTHP cases are
         unaffected: mthp_push_target_order() enables only the target order.
     
    +    A -c at or below -s is refused before any case runs: the sources would
    +    already be the size being asked for.  Without the check the generic cases
    +    fail on that one by one instead of saying why.
    +
         "-s 5 -c 7" on arm64/64K then collapses contpte-mapped sources into a
         larger mTHP.
     
    @@ tools/testing/selftests/mm/khugepaged.c: static void usage(void)
      	exit(1);
      }
      
    +@@ tools/testing/selftests/mm/khugepaged.c: int main(int argc, char **argv)
    + 	    !(thp_supported_orders() & (1UL << collapse_order)))
    + 		ksft_exit_skip("Order %d is not a supported anon THP order\n",
    + 			       collapse_order);
    ++	if (mthp_khugepaged_context && collapse_order <= anon_order)
    ++		ksft_exit_skip("-c %d needs a source order below it, -s says %d\n",
    ++			       collapse_order, anon_order);
    + 
    + 	if (mthp_khugepaged_context) {
    + 		pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
13:  d2251908b73f ! 13:  39a895e66cf1 selftests/mm: cover a shared-source collapse write race
    @@ tools/testing/selftests/mm/khugepaged.c: static void collapse_max_ptes_shared(st
     +	close(sync[1]);
     +	if (read(sync[0], &go, 1) != 1)
     +		ksft_exit_fail_msg("child never reached the collapse\n");
    ++	close(sync[0]);
     +
     +	/*
     +	 * Unshare one page at a time: a burst would break CoW on the whole
    @@ tools/testing/selftests/mm/khugepaged.c: static void collapse_max_ptes_shared(st
     +	 */
     +	i = 0;
     +	for (;;) {
    ++		pid_t ret;
    ++
     +		if (i < n)
     +			ip[i * stride] = i + 0xbeef0000;
     +		i++;
     +		usleep(10 * 1000);
    -+		if (waitpid(child, &wstatus, WNOHANG))
    ++		ret = waitpid(child, &wstatus, WNOHANG);
    ++		if (ret == child)
     +			break;
    ++		if (ret < 0)
    ++			ksft_exit_fail_perror("waitpid()");
     +	}
     +
     +	/* Finish whatever the paced sweep did not reach */
14:  30e316efbd9f ! 14:  8e214f9ef2ea selftests/mm: run every supported collapse order by default
    @@ Commit message
         and "all".  Also:
     
           - -c still pins one order, and now says what is wrong instead of
    -        printing the usage text.  An order at or below the -s source order is
    -        skipped: the sources would already be the size being asked for.
    +        printing the usage text.
     
           - Both orders end up as array indices and shift counts, so -s and -c
             are range-checked before they get there.
    @@ Commit message
         pinned order-4 line.
     
         Assisted-by: LLM
    +    Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
         Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
    +    Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
         Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
     
      ## tools/testing/selftests/mm/khugepaged.c ##
    @@ tools/testing/selftests/mm/khugepaged.c: int main(int argc, char **argv)
     -	    !(thp_supported_orders() & (1UL << collapse_order)))
     -		ksft_exit_skip("Order %d is not a supported anon THP order\n",
     -			       collapse_order);
    +-	if (mthp_khugepaged_context && collapse_order <= anon_order)
    +-		ksft_exit_skip("-c %d needs a source order below it, -s says %d\n",
    +-			       collapse_order, anon_order);
     +	if (mthp_khugepaged_context) {
     +		unsigned long orders = thp_supported_orders();
     +
15:  e891ab107e3a ! 15:  95ae01ec50dd selftests/mm: check that one khugepaged pass collapses one window
    @@ tools/testing/selftests/mm/Makefile: TEST_GEN_FILES += merge
      TEST_GEN_FILES += folio_split_race_test
      TEST_GEN_FILES += folio_order_check
     +TEST_GEN_FILES += khugepaged_sync_check
    - 
    - ifneq ($(ARCH),arm64)
      TEST_GEN_FILES += soft-dirty
    + 
    + ifeq ($(ARCH),x86_64)
     
      ## tools/testing/selftests/mm/khugepaged_sync_check.c (new) ##
     @@
    @@ tools/testing/selftests/mm/khugepaged_sync_check.c (new)
     +
     +#include "kselftest.h"
     +#include "vm_util.h"
    -+#include "hugepage_settings.h"
    ++#include <mm/hugepage_settings.h>
     +
     +#define BASE_ADDR ((void *)(1UL << 30))
     +/* Smallest order khugepaged considers */
16:  d7f8e59c19f1 ! 16:  343b8684a8bd selftests/mm: add khugepaged race harness
    @@ tools/testing/selftests/mm/Makefile: TEST_GEN_FILES += rmap
      TEST_GEN_FILES += folio_order_check
      TEST_GEN_FILES += khugepaged_sync_check
     +TEST_GEN_FILES += khugepaged_race
    - 
    - ifneq ($(ARCH),arm64)
      TEST_GEN_FILES += soft-dirty
    + 
    + ifeq ($(ARCH),x86_64)
     
      ## tools/testing/selftests/mm/khugepaged_race.c (new) ##
     @@
    @@ tools/testing/selftests/mm/khugepaged_race.c (new)
     +
     +#include "kselftest.h"
     +#include "vm_util.h"
    -+#include "hugepage_settings.h"
    ++#include <mm/hugepage_settings.h>
     +#include "../../../../mm/gup_test.h"
     +
     +#ifndef FOLL_WRITE
    @@ tools/testing/selftests/mm/khugepaged_race.c (new)
     +			   MREMAP_MAYMOVE | MREMAP_FIXED, mremap_area);
     +		if (p == MAP_FAILED)
     +			ksft_exit_fail_perror("mremap() back");
    ++		/* The move back unmapped the scratch address: claim it again */
    ++		if (mmap(mremap_scratch, hpage_pmd_size, PROT_NONE,
    ++			 MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE,
    ++			 -1, 0) != (void *)mremap_scratch)
    ++			ksft_exit_fail_perror("mmap() mremap scratch");
     +		usleep(rand_r(&seed) % 2000);
     +	}
     +	return NULL;
17:  f85220ed8bb4 = 17:  09cfcb6afbc4 selftests/mm: race the collapse of windows with holes
18:  b3738ea322b7 = 18:  b12f1f2d500c selftests/mm: add memory-pressure threads to the khugepaged race harness
19:  66f5a400e015 = 19:  ad0be4f7ec43 selftests/mm: zap whole PTE tables in the khugepaged race harness

Kiryl Shutsemau (Meta) (19):
  selftests/mm: raise the khugepaged test-case cap
  selftests/mm: skip collapse_compound_extreme() where the PMD is too
    large
  selftests/mm: scale khugepaged's collapse wait with the PMD size
  selftests/mm: skip khugepaged page cache cases without a PMD folio
  selftests/mm: make the swap cases' swapout reliable
  selftests/mm: stop khugepaged during the MADV_COLLAPSE cases
  selftests/mm: move is_backed_by_folio() into vm_util
  selftests/mm: add folio-order check for address ranges
  selftests/mm: add folio-order detection self-check
  selftests/mm: add khugepaged completion barrier helper
  selftests/mm: add order-parameterized khugepaged collapse cases
  selftests/mm: parameterize the mixed-source collapse case by source
    order
  selftests/mm: cover a shared-source collapse write race
  selftests/mm: run every supported collapse order by default
  selftests/mm: check that one khugepaged pass collapses one window
  selftests/mm: add khugepaged race harness
  selftests/mm: race the collapse of windows with holes
  selftests/mm: add memory-pressure threads to the khugepaged race
    harness
  selftests/mm: zap whole PTE tables in the khugepaged race harness

 tools/lib/mm/hugepage_settings.c              |  60 +-
 tools/lib/mm/hugepage_settings.h              |  11 +
 tools/testing/selftests/mm/Makefile           |   3 +
 .../testing/selftests/mm/folio_order_check.c  | 122 ++++
 tools/testing/selftests/mm/hmm-tests.c        |   1 -
 tools/testing/selftests/mm/khugepaged.c       | 488 +++++++++++++++-
 tools/testing/selftests/mm/khugepaged_race.c  | 538 ++++++++++++++++++
 .../selftests/mm/khugepaged_sync_check.c      | 179 ++++++
 tools/testing/selftests/mm/migration.c        |   1 -
 tools/testing/selftests/mm/run_vmtests.sh     |   8 +-
 .../selftests/mm/split_huge_page_test.c       |  61 --
 tools/testing/selftests/mm/vm_util.c          | 146 +++++
 tools/testing/selftests/mm/vm_util.h          |  10 +
 13 files changed, 1526 insertions(+), 102 deletions(-)
 create mode 100644 tools/testing/selftests/mm/folio_order_check.c
 create mode 100644 tools/testing/selftests/mm/khugepaged_race.c
 create mode 100644 tools/testing/selftests/mm/khugepaged_sync_check.c


base-commit: 498ee28e5ec4727f829507c4a1bde3ab1b7704cd
-- 
2.54.0

[PATCH v6 01/19] selftests/mm: raise the khugepaged test-case cap

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

TEST() ends the run with "MAX_TEST_CASES is too small" when the table
fills, and the table holds 64.  A full invocation already registers 63, so
the next case added anywhere aborts the whole suite before a single test
runs.

Raise the cap to 256.  The table is a static array of small structs, so the
room costs nothing worth counting.

Assisted-by: LLM
Acked-by: Usama Arif <usama.arif@linux.dev>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 525108cace54..c44bc18f7536 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1290,7 +1290,7 @@ struct test_case {
 	test_fn fn;
 };
 
-#define MAX_TEST_CASES 64
+#define MAX_TEST_CASES 256
 static struct test_case test_cases[MAX_TEST_CASES];
 static int nr_test_cases;
 
-- 
2.54.0

[PATCH v6 02/19] selftests/mm: skip collapse_compound_extreme() where the PMD is too large

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

collapse_compound_extreme() builds a PTE table full of distinct PTE-mapped
compound pages by cycling hpage_pmd_nr fault-time THPs through mremap.  It
therefore needs hpage_pmd_nr PMD-order allocations in a row.  That is fine
at a 2M PMD (4K base pages) or a 32M one (16K).  A 512M PMD -- arm64 with
64K base pages -- makes each of those an order-13 allocation, which the
allocator cannot reliably hand out even once, let alone 8192 times.

The failure is not a quiet one: the case calls ksft_exit_fail_msg(), so the
whole binary stops and every case after it is lost.

Skip the case where the PMD is larger than 32M.  The MADV_COLLAPSE cases
still cover PMD-order collapse on those configurations, and 4K and 16K
PMDs are unaffected.

Assisted-by: LLM
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index c44bc18f7536..8a6d708026b7 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -940,6 +940,16 @@ static void collapse_compound_extreme(struct collapse_context *c, struct mem_ops
 	void *p;
 	int i;
 
+	/*
+	 * This needs hpage_pmd_nr PMD-order allocations in a row, which the
+	 * allocator will not supply if the PMD is very large.
+	 */
+	if (hpage_pmd_size > (32UL << 20)) {
+		ksft_test_result_skip("%s: PMD too large for fault-time THP construction\n",
+				      __func__);
+		return;
+	}
+
 	p = ops->setup_area(1);
 	ksft_print_msg("Construct PTE page table full of different PTE-mapped compound pages\n");
 	for (i = 0; i < hpage_pmd_nr; i++) {
-- 
2.54.0

[PATCH v6 03/19] selftests/mm: scale khugepaged's collapse wait with the PMD size

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

wait_for_scan() gives every case the same three seconds, whatever the huge
page costs to build.  collapse_full() asks for four of them: 8M at a 2M
PMD, but 2G at a 512M PMD -- arm64 with 64K base pages.  Three seconds is
thin at that size, and the case has reported a failure for a collapse that
was still going.

The timeout is a ceiling on a poll loop, not a sleep: the loop stops as
soon as ops->check_huge() sees the collapse, or as soon as full_scans has
advanced by two.  Raising it costs a passing case nothing.  Across 80 runs
of collapse_full() on arm64 with 64K pages the wait was half a second in
73 of them, with a tail to two seconds.

Keep three seconds as the floor and add a second per 128M collapsed.  A 2M
PMD is unchanged, so x86-64 is too; a 512M PMD gets 19 seconds.

On arm64 with 64K pages a passing ./khugepaged all:anon takes 49 seconds
under TCG before and after this change.

Assisted-by: LLM
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 8a6d708026b7..189cc4fee18f 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -561,8 +561,11 @@ static bool wait_for_scan(const char *msg, char *p, size_t len,
 		int nr_hpages, int collap_order, struct mem_ops *ops)
 {
 	unsigned long hpage_size = page_size << collap_order;
-	int full_scans;
-	int timeout = 6; /* 3 seconds */
+	unsigned long bytes = (unsigned long)nr_hpages * hpage_size;
+	int timeout, full_scans;
+
+	/* Half-second ticks: three seconds floor, plus a second per 128M */
+	timeout = 6 + 2 * (bytes / (128UL << 20));
 
 	/* Sanity check */
 	if (!ops->check_huge(p, len, 0, hpage_size))
-- 
2.54.0

[PATCH v6 04/19] selftests/mm: skip khugepaged page cache cases without a PMD folio

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The page cache caps folio order at MAX_PAGECACHE_ORDER, which is below the
PMD order on arm64 with 64K pages, where a PMD is 512M.  A PMD-sized page
cache folio is impossible there, so the kernel refuses these collapses:
MADV_COLLAPSE answers -EINVAL and khugepaged passes over the range.  Four
shmem cases ask for a PMD-sized folio anyway, fail, and the run bails out
in the middle.

Skip the shmem and file mem types where the cap is below the PMD order.

The cap is not shmem-specific: it applies to every file folio.  Add
thp_file_supported_orders() to read the orders the page cache allows.

Anonymous collapse is unaffected: its orders are not capped this way.

Assisted-by: LLM
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/lib/mm/hugepage_settings.h        |  9 +++++++++
 tools/testing/selftests/mm/khugepaged.c | 19 +++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/tools/lib/mm/hugepage_settings.h b/tools/lib/mm/hugepage_settings.h
index 548e9d288d1d..94d9fc747f49 100644
--- a/tools/lib/mm/hugepage_settings.h
+++ b/tools/lib/mm/hugepage_settings.h
@@ -87,6 +87,15 @@ void thp_set_read_ahead_path(char *path);
 unsigned long thp_supported_orders(void);
 unsigned long thp_shmem_supported_orders(void);
 
+/*
+ * The per-order shmem_enabled attribute is created for the orders the page
+ * cache can hold, not just for shmem, so it answers for regular files too.
+ */
+static inline unsigned long thp_file_supported_orders(void)
+{
+	return thp_shmem_supported_orders();
+}
+
 bool thp_available(void);
 bool thp_is_enabled(void);
 
diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 189cc4fee18f..5318f3cfc0d0 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1358,6 +1358,25 @@ int main(int argc, char **argv)
 
 	setbuf(stdout, NULL);
 
+	/*
+	 * Without a PMD-order page cache folio the kernel refuses these
+	 * collapses, so there is nothing to test.
+	 */
+	if (!(thp_file_supported_orders() & (1UL << hpage_pmd_order))) {
+		if (shmem_ops) {
+			ksft_print_msg("no PMD-order page cache folio: skipping shmem\n");
+			shmem_ops = NULL;
+		}
+		if (read_only_file_ops) {
+			ksft_print_msg("no PMD-order page cache folio: skipping file\n");
+			read_only_file_ops = NULL;
+			read_write_file_read_ops = NULL;
+			read_write_file_write_ops = NULL;
+		}
+		if (!anon_ops && !shmem_ops && !read_only_file_ops)
+			ksft_exit_skip("No mem_type left to run\n");
+	}
+
 	default_settings.khugepaged.max_ptes_none = hpage_pmd_nr - 1;
 	default_settings.khugepaged.max_ptes_swap = hpage_pmd_nr / 8;
 	default_settings.khugepaged.max_ptes_shared = hpage_pmd_nr / 2;
-- 
2.54.0

[PATCH v6 05/19] selftests/mm: make the swap cases' swapout reliable

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

collapse_swapin_single_pte() and collapse_max_ptes_swap() swap a range out
and then require smaps to report exactly the count they asked for.  Two
things keep that count from arriving.

MADV_PAGEOUT is best effort, so the count often turns up a moment late.

And wait_for_scan() leaves the range eligible for collapsing, so
khugepaged is still working on it.  Collapsing reads the swapped-out pages
back in, so the daemon empties the swap as fast as the case fills it.  On
arm64 with 64K pages max_ptes_swap is 1024 pages, which is 64M a step, and
the case loses the race:

    # Swapout 1024 of 8192 pages... Fail
    not ok 10 collapse_max_ptes_swap

Retry for up to two seconds, holding the range out of khugepaged's reach
meanwhile.  The collapse each case runs next restores MADV_HUGEPAGE, so
only the setup is affected.

If the pages still won't swap out, skip: no swap, swap too small or full,
a memcg cap or busy writeback. None of that is a kernel bug.

Assisted-by: LLM
Reviewed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 41 +++++++++++++++++--------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 5318f3cfc0d0..13a2a47ab110 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -221,6 +221,29 @@ static bool check_swap(void *addr, unsigned long size)
 	return swap;
 }
 
+static bool swapout_range(void *p, unsigned long size)
+{
+	int i;
+
+	/* keep khugepaged from collapsing the range and swapping it back in */
+	if (madvise(p, size, MADV_NOHUGEPAGE))
+		ksft_exit_fail_perror("madvise(MADV_NOHUGEPAGE)");
+
+	/*
+	 * Retry several times because MADV_PAGEOUT is best effort.  Sleep
+	 * between the retries to give outstanding writeback a chance to
+	 * finish.
+	 */
+	for (i = 0; i < 40; i++) {
+		if (madvise(p, size, MADV_PAGEOUT))
+			ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
+		if (check_swap(p, size))
+			return true;
+		usleep(50 * 1000);
+	}
+	return false;
+}
+
 static void *alloc_mapping(int nr)
 {
 	void *p;
@@ -828,12 +851,10 @@ static void collapse_swapin_single_pte(struct collapse_context *c, struct mem_op
 	ops->fault(p, 0, hpage_pmd_size);
 
 	ksft_print_msg("Swapout one page...");
-	if (madvise(p, page_size, MADV_PAGEOUT))
-		ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
-	if (check_swap(p, page_size)) {
+	if (swapout_range(p, page_size)) {
 		success("OK");
 	} else {
-		fail("Fail");
+		skip("Could not swap out");
 		goto out;
 	}
 
@@ -854,12 +875,10 @@ static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *o
 	ops->fault(p, 0, hpage_pmd_size);
 
 	ksft_print_msg("Swapout %d of %d pages...", max_ptes_swap + 1, hpage_pmd_nr);
-	if (madvise(p, (max_ptes_swap + 1) * page_size, MADV_PAGEOUT))
-		ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
-	if (check_swap(p, (max_ptes_swap + 1) * page_size)) {
+	if (swapout_range(p, (max_ptes_swap + 1) * page_size)) {
 		success("OK");
 	} else {
-		fail("Fail");
+		skip("Could not swap out");
 		goto out;
 	}
 
@@ -871,12 +890,10 @@ static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *o
 		ops->fault(p, 0, hpage_pmd_size);
 		ksft_print_msg("Swapout %d of %d pages...", max_ptes_swap,
 		       hpage_pmd_nr);
-		if (madvise(p, max_ptes_swap * page_size, MADV_PAGEOUT))
-			ksft_exit_fail_perror("madvise(MADV_PAGEOUT)");
-		if (check_swap(p, max_ptes_swap * page_size)) {
+		if (swapout_range(p, max_ptes_swap * page_size)) {
 			success("OK");
 		} else {
-			fail("Fail");
+			skip("Could not swap out");
 			goto out;
 		}
 
-- 
2.54.0

[PATCH v6 06/19] selftests/mm: stop khugepaged during the MADV_COLLAPSE cases

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

__madvise_collapse() turns THP off before each MADV_COLLAPSE, both to keep
khugepaged out of the range and to prove MADV_COLLAPSE ignores the setting.
It clears the global controls only, which is no longer enough.  A per-order
control overrides them, and -s, which makes the cases fault in folios of
one order, leaves that order's control at "always".  khugepaged then
collapses the very range the case is working on, and the case fails on a
collapse that was interfered with rather than refused.

Clear the per-order controls too.  MADV_COLLAPSE does not consult them:
anon never did, and shmem stopped with "mm: shmem: ignore sysfs configs
for shmem forced collapse".

Fixes: b7f16963efe7 ("mm/khugepaged: run khugepaged for all orders")
Assisted-by: LLM
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 13a2a47ab110..e013eebc7136 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -538,8 +538,8 @@ static bool is_anon(struct mem_ops *ops)
 static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
 			       struct mem_ops *ops, bool expect)
 {
-	int ret;
 	struct thp_settings settings = *thp_current_settings();
+	int ret, i;
 
 	ksft_print_msg("%s...", msg);
 
@@ -555,6 +555,10 @@ static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
 	 */
 	settings.thp_enabled = THP_NEVER;
 	settings.shmem_enabled = SHMEM_NEVER;
+	for (i = 0; i < NR_ORDERS; i++) {
+		settings.hugepages[i].enabled = THP_NEVER;
+		settings.shmem_hugepages[i].enabled = SHMEM_NEVER;
+	}
 	thp_push_settings(&settings);
 
 	/* Clear VM_NOHUGEPAGE */
-- 
2.54.0

[PATCH v6 07/19] selftests/mm: move is_backed_by_folio() into vm_util

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

Checking that an address range is backed by a folio of a given order is
useful to any test that builds or collapses large folios.  mTHP collapse
coverage in the khugepaged selftest needs exactly that.

split_huge_page_test.c already has the building block:
is_backed_by_folio() reads the compound head and tail flags from
/proc/kpageflags to classify the folio behind a page.

Move it into vm_util so other tests can use it.  No functional change.

Assisted-by: LLM
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 .../selftests/mm/split_huge_page_test.c       | 61 -------------------
 tools/testing/selftests/mm/vm_util.c          | 61 +++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h          |  2 +
 3 files changed, 63 insertions(+), 61 deletions(-)

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 68f508c9a355..c5d96a4b1db3 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -41,67 +41,6 @@ const char *kpageflags_proc = "/proc/kpageflags";
 int pagemap_fd;
 int kpageflags_fd;
 
-static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
-		int kpageflags_fd)
-{
-	const uint64_t folio_head_flags = KPF_THP | KPF_COMPOUND_HEAD;
-	const uint64_t folio_tail_flags = KPF_THP | KPF_COMPOUND_TAIL;
-	const unsigned long nr_pages = 1UL << order;
-	unsigned long pfn_head;
-	uint64_t pfn_flags;
-	unsigned long pfn;
-	unsigned long i;
-
-	pfn = pagemap_get_pfn(pagemap_fd, vaddr);
-
-	/* non present page */
-	if (pfn == -1UL)
-		return false;
-
-	if (pageflags_get(pfn, kpageflags_fd, &pfn_flags))
-		goto fail;
-
-	/* check for order-0 pages */
-	if (!order) {
-		if (pfn_flags & (folio_head_flags | folio_tail_flags))
-			return false;
-		return true;
-	}
-
-	/* non THP folio */
-	if (!(pfn_flags & KPF_THP))
-		return false;
-
-	pfn_head = pfn & ~(nr_pages - 1);
-
-	if (pageflags_get(pfn_head, kpageflags_fd, &pfn_flags))
-		goto fail;
-
-	/* head PFN has no compound_head flag set */
-	if ((pfn_flags & folio_head_flags) != folio_head_flags)
-		return false;
-
-	/* check all tail PFN flags */
-	for (i = 1; i < nr_pages; i++) {
-		if (pageflags_get(pfn_head + i, kpageflags_fd, &pfn_flags))
-			goto fail;
-		if ((pfn_flags & folio_tail_flags) != folio_tail_flags)
-			return false;
-	}
-
-	/*
-	 * check the PFN after this folio, but if its flags cannot be obtained,
-	 * assume this folio has the expected order
-	 */
-	if (pageflags_get(pfn_head + nr_pages, kpageflags_fd, &pfn_flags))
-		return true;
-
-	/* If we find another tail page, then the folio is larger. */
-	return (pfn_flags & folio_tail_flags) != folio_tail_flags;
-fail:
-	ksft_exit_fail_msg("Failed to get folio info\n");
-}
-
 static int check_after_split_folio_orders(char *vaddr_start, size_t len,
 		int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders)
 {
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 4751db798c3a..cc5dfd1e6c94 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -494,6 +494,67 @@ int pageflags_get(unsigned long pfn, int kpageflags_fd, uint64_t *flags)
 	return 0;
 }
 
+bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
+			int kpageflags_fd)
+{
+	const uint64_t folio_head_flags = KPF_THP | KPF_COMPOUND_HEAD;
+	const uint64_t folio_tail_flags = KPF_THP | KPF_COMPOUND_TAIL;
+	const unsigned long nr_pages = 1UL << order;
+	unsigned long pfn_head;
+	uint64_t pfn_flags;
+	unsigned long pfn;
+	unsigned long i;
+
+	pfn = pagemap_get_pfn(pagemap_fd, vaddr);
+
+	/* non present page */
+	if (pfn == -1UL)
+		return false;
+
+	if (pageflags_get(pfn, kpageflags_fd, &pfn_flags))
+		goto fail;
+
+	/* check for order-0 pages */
+	if (!order) {
+		if (pfn_flags & (folio_head_flags | folio_tail_flags))
+			return false;
+		return true;
+	}
+
+	/* non THP folio */
+	if (!(pfn_flags & KPF_THP))
+		return false;
+
+	pfn_head = pfn & ~(nr_pages - 1);
+
+	if (pageflags_get(pfn_head, kpageflags_fd, &pfn_flags))
+		goto fail;
+
+	/* head PFN has no compound_head flag set */
+	if ((pfn_flags & folio_head_flags) != folio_head_flags)
+		return false;
+
+	/* check all tail PFN flags */
+	for (i = 1; i < nr_pages; i++) {
+		if (pageflags_get(pfn_head + i, kpageflags_fd, &pfn_flags))
+			goto fail;
+		if ((pfn_flags & folio_tail_flags) != folio_tail_flags)
+			return false;
+	}
+
+	/*
+	 * check the PFN after this folio, but if its flags cannot be obtained,
+	 * assume this folio has the expected order
+	 */
+	if (pageflags_get(pfn_head + nr_pages, kpageflags_fd, &pfn_flags))
+		return true;
+
+	/* If we find another tail page, then the folio is larger. */
+	return (pfn_flags & folio_tail_flags) != folio_tail_flags;
+fail:
+	ksft_exit_fail_msg("Failed to get folio info\n");
+}
+
 /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 64a86e8a0c41..f12979a70135 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -99,6 +99,8 @@ int64_t allocate_transhuge(void *ptr, int pagemap_fd);
 int pageflags_get(unsigned long pfn, int kpageflags_fd, uint64_t *flags);
 int gather_folio_orders(char *vaddr_start, size_t len,
 		int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders);
+bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
+			int kpageflags_fd);
 
 int uffd_register(int uffd, void *addr, uint64_t len,
 		  bool miss, bool wp, bool minor);
-- 
2.54.0

[PATCH v6 08/19] selftests/mm: add folio-order check for address ranges

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

An mTHP collapse test needs to know that a range is backed by folios of the
target order, and that they sit where a collapse would put them.  Nothing
answers both: is_backed_by_folio() classifies the folio behind a single
page, and check_huge_anon() counts the folios of an order in a range
without saying where they start.

Add is_range_backed_by_order().  It requires every folio-sized, folio-
aligned part of the range to map one folio of that order, head to tail,
with the head at the start of the part.

A part backed by two smaller folios fails, and so does a folio mapped off
its natural alignment.  The mTHP cases need both to tell a collapsed range
from the one beside it.

Assisted-by: LLM
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/vm_util.c | 47 ++++++++++++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h |  2 ++
 2 files changed, 49 insertions(+)

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index cc5dfd1e6c94..c8c5cd8ab6c1 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -555,6 +555,53 @@ bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
 	ksft_exit_fail_msg("Failed to get folio info\n");
 }
 
+/**
+ * is_range_backed_by_order() - check that a range is backed by @order folios
+ * @start: start of the range, a multiple of the folio size
+ * @len: length of the range in bytes, a multiple of the folio size
+ * @order: the folio order to check for
+ * @pagemap_fd: open /proc/<pid>/pagemap of the range's owner
+ * @kpageflags_fd: open /proc/kpageflags
+ *
+ * Every folio-sized, folio-aligned part of the range must map one folio of
+ * @order, head to tail, with the head at the start of the part.  A part
+ * backed by several smaller folios fails, and so does a folio mapped off
+ * its natural alignment.
+ *
+ * Returns: true if the whole range is backed that way, false otherwise.
+ */
+bool is_range_backed_by_order(char *start, size_t len, int order,
+			      int pagemap_fd, int kpageflags_fd)
+{
+	const unsigned long nr_pages = 1UL << order;
+	const size_t folio_size = nr_pages * psize();
+	char *vaddr;
+
+	if ((uintptr_t)start % folio_size || len % folio_size)
+		return false;
+
+	for (vaddr = start; vaddr < start + len; vaddr += folio_size) {
+		const unsigned long pfn = pagemap_get_pfn(pagemap_fd, vaddr);
+		unsigned long i;
+
+		/* Not present, or a tail page */
+		if (pfn == -1UL || pfn % nr_pages)
+			return false;
+
+		for (i = 1; i < nr_pages; i++) {
+			char *page = vaddr + i * psize();
+
+			if (pagemap_get_pfn(pagemap_fd, page) != pfn + i)
+				return false;
+		}
+
+		if (!is_backed_by_folio(vaddr, order, pagemap_fd, kpageflags_fd))
+			return false;
+	}
+
+	return true;
+}
+
 /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index f12979a70135..0172003c16dc 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -101,6 +101,8 @@ int gather_folio_orders(char *vaddr_start, size_t len,
 		int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders);
 bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
 			int kpageflags_fd);
+bool is_range_backed_by_order(char *start, size_t len, int order,
+			      int pagemap_fd, int kpageflags_fd);
 
 int uffd_register(int uffd, void *addr, uint64_t len,
 		  bool miss, bool wp, bool minor);
-- 
2.54.0

[PATCH v6 09/19] selftests/mm: add folio-order detection self-check

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The khugepaged mTHP tests detect collapse results with the vm_util
folio-order helpers rather than smaps AnonHugePages, which only sees PMD
mappings.  If those helpers are wrong, every case built on them is wrong
the same way, and nothing says so.

Check them directly.  For every anon THP order the kernel supports, fault
memory in with only that order enabled.  Require the helpers to classify
the backing as exactly that order: not the order below it, and base-page
memory as order 0.

Run it in the thp category, ahead of ./khugepaged, so a broken helper is
reported as itself rather than as a collapse failure.  Verified on x86-64
4K (orders 0, 2-9) and arm64 64K (orders 0, 2-13).

The test needs ALIGN(), which hmm-tests.c and migration.c each defined
privately.  Move it to vm_util.h and drop both copies.

Assisted-by: LLM
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/Makefile           |   1 +
 .../testing/selftests/mm/folio_order_check.c  | 122 ++++++++++++++++++
 tools/testing/selftests/mm/hmm-tests.c        |   1 -
 tools/testing/selftests/mm/migration.c        |   1 -
 tools/testing/selftests/mm/run_vmtests.sh     |   2 +
 tools/testing/selftests/mm/vm_util.h          |   2 +
 6 files changed, 127 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/mm/folio_order_check.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 7d69baeb93f4..cb32cf5d867e 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -105,6 +105,7 @@ TEST_GEN_FILES += guard-regions
 TEST_GEN_FILES += merge
 TEST_GEN_FILES += rmap
 TEST_GEN_FILES += folio_split_race_test
+TEST_GEN_FILES += folio_order_check
 TEST_GEN_FILES += soft-dirty
 
 ifeq ($(ARCH),x86_64)
diff --git a/tools/testing/selftests/mm/folio_order_check.c b/tools/testing/selftests/mm/folio_order_check.c
new file mode 100644
index 000000000000..5eafbcc1b4f3
--- /dev/null
+++ b/tools/testing/selftests/mm/folio_order_check.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Self-check for the vm_util folio-order helpers, is_backed_by_folio() and
+ * is_range_backed_by_order(), which the khugepaged mTHP cases use to detect
+ * collapse results.  For every anon THP order the kernel supports, fault
+ * memory in with only that order enabled and require the helpers to report
+ * exactly that order.
+ */
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "kselftest.h"
+#include "vm_util.h"
+#include <mm/hugepage_settings.h>
+
+static int pagemap_fd;
+static int kpageflags_fd;
+
+static char *alloc_aligned(size_t size)
+{
+	size_t len = size * 2;
+	char *p, *aligned;
+
+	p = mmap(NULL, len, PROT_READ | PROT_WRITE,
+		 MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	if (p == MAP_FAILED)
+		ksft_exit_fail_perror("mmap()");
+
+	aligned = (char *)ALIGN((uintptr_t)p, size);
+	if (aligned != p)
+		munmap(p, aligned - p);
+	if (aligned + size != p + len)
+		munmap(aligned + size, p + len - aligned - size);
+
+	return aligned;
+}
+
+static void check_order(int order)
+{
+	struct thp_settings settings = *thp_current_settings();
+	size_t size = psize() << order;
+	bool ok = true;
+	char *p;
+	int i;
+
+	for (i = 0; i < NR_ORDERS; i++)
+		settings.hugepages[i].enabled = THP_NEVER;
+	if (order)
+		settings.hugepages[order].enabled = THP_ALWAYS;
+	thp_push_settings(&settings);
+
+	p = alloc_aligned(size);
+	*p = 1;
+
+	if (!is_range_backed_by_order(p, size, order, pagemap_fd, kpageflags_fd)) {
+		ksft_print_msg("order %d not detected after fault\n", order);
+		ok = false;
+	}
+
+	/* A lower order must be rejected: the folio is larger */
+	if (order && is_range_backed_by_order(p, size, order - 1,
+					      pagemap_fd, kpageflags_fd)) {
+		ksft_print_msg("order %d also reported as order %d\n",
+			       order, order - 1);
+		ok = false;
+	}
+
+	/* A large folio must not pass as order 0 */
+	if (order && is_range_backed_by_order(p, size, 0,
+					      pagemap_fd, kpageflags_fd)) {
+		ksft_print_msg("order %d also reported as order 0\n", order);
+		ok = false;
+	}
+
+	munmap(p, size);
+	thp_pop_settings();
+
+	ksft_test_result(ok, "order %d classified\n", order);
+}
+
+int main(void)
+{
+	struct thp_settings settings;
+	unsigned long orders;
+	int order;
+
+	ksft_print_header();
+
+	if (!thp_available())
+		ksft_exit_skip("Transparent Hugepages not available\n");
+
+	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	if (pagemap_fd < 0)
+		ksft_exit_fail_perror("open(/proc/self/pagemap)");
+	kpageflags_fd = open("/proc/kpageflags", O_RDONLY);
+	if (kpageflags_fd < 0)
+		ksft_exit_skip("open(/proc/kpageflags) requires root\n");
+
+	orders = thp_supported_orders();
+	if (!orders)
+		ksft_exit_skip("No supported THP orders\n");
+
+	ksft_set_plan(__builtin_popcountl(orders) + 1);
+
+	thp_save_settings();
+	thp_read_settings(&settings);
+	/* Base of the settings stack; the bottom entry is never popped */
+	thp_push_settings(&settings);
+
+	check_order(0);
+	for (order = 1; order < NR_ORDERS; order++) {
+		if (!(orders & (1UL << order)))
+			continue;
+		check_order(order);
+	}
+
+	ksft_finished();
+}
diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
index fa1a651963fd..e5f273ca84c1 100644
--- a/tools/testing/selftests/mm/hmm-tests.c
+++ b/tools/testing/selftests/mm/hmm-tests.c
@@ -65,7 +65,6 @@ enum {
 #define HMM_PATH_MAX    64
 #define NTIMES		10
 
-#define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))
 /* Just the flags we need, copied from mm.h: */
 
 #ifndef FOLL_WRITE
diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftests/mm/migration.c
index a35e2b57e05b..d1d0989ed2ca 100644
--- a/tools/testing/selftests/mm/migration.c
+++ b/tools/testing/selftests/mm/migration.c
@@ -20,7 +20,6 @@
 
 #define TWOMEG		(2<<20)
 #define RUNTIME		(20)
-#define ALIGN(x, a)	(((x) + (a - 1)) & (~((a) - 1)))
 
 HUGETLB_SETUP_DEFAULT_PAGES(1)
 
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 4cc1d1a55ebf..3a111bc9c29e 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -382,6 +382,8 @@ CATEGORY="pfnmap" run_test ./pfnmap
 # COW tests
 CATEGORY="cow" run_test ./cow
 
+CATEGORY="thp" run_test ./folio_order_check
+
 CATEGORY="thp" run_test ./khugepaged
 
 CATEGORY="thp" run_test ./khugepaged -s 2
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 0172003c16dc..ea48e6a7527e 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -12,6 +12,8 @@
 #include <mm/hugepage_settings.h>
 
 #define BIT_ULL(nr)                   (1ULL << (nr))
+#define ALIGN(x, a)                   (((x) + (a) - 1) & ~((a) - 1))
+
 #define PM_SOFT_DIRTY                 BIT_ULL(55)
 #define PM_MMAP_EXCLUSIVE             BIT_ULL(56)
 #define PM_UFFD_WP                    BIT_ULL(57)
-- 
2.54.0

[PATCH v6 10/19] selftests/mm: add khugepaged completion barrier helper

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

A khugepaged test has to tell "not collapsed" from "not scanned yet", and
nothing in the selftests can.  wait_for_scan() in khugepaged.c comes
closest: it polls full_scans until the counter has advanced by two, since
the pass in progress may already have passed the test's mm.  But it only
returns in time if scan_sleep_millisecs happens to be short, and it is
private to that one test.

Add khugepaged_full_pass() to hugepage_settings, built on the same
advance-by-two wait but driven through sysfs: a store to
scan_sleep_millisecs wakes the daemon, so the barrier completes whatever
the scan cadence.  A store made while the daemon is scanning rather than
sleeping is lost, so the helper keeps storing until the pass lands.

One wake completes one pass only if pages_to_scan covers every mm on the
list, so callers need it large.

Settings pushes must not start passes of their own.  A store to either
sleep knob wakes the daemon, so thp_write_settings() now writes a
khugepaged knob only when its value changes.

Assisted-by: LLM
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/lib/mm/hugepage_settings.c | 60 +++++++++++++++++++++++++++-----
 tools/lib/mm/hugepage_settings.h |  2 ++
 2 files changed, 53 insertions(+), 9 deletions(-)

diff --git a/tools/lib/mm/hugepage_settings.c b/tools/lib/mm/hugepage_settings.c
index 656442c8d395..77918677a9cd 100644
--- a/tools/lib/mm/hugepage_settings.c
+++ b/tools/lib/mm/hugepage_settings.c
@@ -217,6 +217,13 @@ void thp_read_settings(struct thp_settings *settings)
 	}
 }
 
+/* A store to either sleep knob wakes khugepaged, so write only on change */
+static void thp_update_num(const char *name, unsigned long num)
+{
+	if (thp_read_num(name) != num)
+		thp_write_num(name, num);
+}
+
 void thp_write_settings(struct thp_settings *settings)
 {
 	struct khugepaged_settings *khugepaged = &settings->khugepaged;
@@ -232,15 +239,15 @@ void thp_write_settings(struct thp_settings *settings)
 			shmem_enabled_strings[settings->shmem_enabled]);
 	thp_write_num("use_zero_page", settings->use_zero_page);
 
-	thp_write_num("khugepaged/defrag", khugepaged->defrag);
-	thp_write_num("khugepaged/alloc_sleep_millisecs",
-			khugepaged->alloc_sleep_millisecs);
-	thp_write_num("khugepaged/scan_sleep_millisecs",
-			khugepaged->scan_sleep_millisecs);
-	thp_write_num("khugepaged/max_ptes_none", khugepaged->max_ptes_none);
-	thp_write_num("khugepaged/max_ptes_swap", khugepaged->max_ptes_swap);
-	thp_write_num("khugepaged/max_ptes_shared", khugepaged->max_ptes_shared);
-	thp_write_num("khugepaged/pages_to_scan", khugepaged->pages_to_scan);
+	thp_update_num("khugepaged/defrag", khugepaged->defrag);
+	thp_update_num("khugepaged/alloc_sleep_millisecs",
+		       khugepaged->alloc_sleep_millisecs);
+	thp_update_num("khugepaged/scan_sleep_millisecs",
+		       khugepaged->scan_sleep_millisecs);
+	thp_update_num("khugepaged/max_ptes_none", khugepaged->max_ptes_none);
+	thp_update_num("khugepaged/max_ptes_swap", khugepaged->max_ptes_swap);
+	thp_update_num("khugepaged/max_ptes_shared", khugepaged->max_ptes_shared);
+	thp_update_num("khugepaged/pages_to_scan", khugepaged->pages_to_scan);
 
 	if (dev_queue_read_ahead_path[0]) {
 		int ret = write_num(dev_queue_read_ahead_path,
@@ -271,6 +278,41 @@ void thp_write_settings(struct thp_settings *settings)
 	}
 }
 
+/*
+ * Wait for a full khugepaged scan pass that started after this call: the
+ * pass in progress may already have passed this mm, so full_scans has to
+ * advance twice.
+ *
+ * A store to scan_sleep_millisecs wakes the daemon, but one made while it
+ * is scanning rather than sleeping is lost, so keep storing until the pass
+ * lands.
+ *
+ * One wake is one pass only if pages_to_scan covers every mm on the list.
+ */
+bool khugepaged_full_pass(unsigned int timeout_s)
+{
+	unsigned long deadline_ms = timeout_s * 1000UL;
+	unsigned long elapsed_ms = 0, poll_ms = 10;
+	unsigned long sleep_ms;
+	int pass;
+
+	sleep_ms = thp_read_num("khugepaged/scan_sleep_millisecs");
+	for (pass = 0; pass < 2; pass++) {
+		unsigned long target =
+			thp_read_num("khugepaged/full_scans") + 1;
+
+		while (thp_read_num("khugepaged/full_scans") < target) {
+			if (elapsed_ms >= deadline_ms)
+				return false;
+			thp_write_num("khugepaged/scan_sleep_millisecs",
+				      sleep_ms);
+			usleep(poll_ms * 1000);
+			elapsed_ms += poll_ms;
+		}
+	}
+	return true;
+}
+
 struct thp_settings *thp_current_settings(void)
 {
 	if (!settings_index) {
diff --git a/tools/lib/mm/hugepage_settings.h b/tools/lib/mm/hugepage_settings.h
index 94d9fc747f49..8f4581099b7a 100644
--- a/tools/lib/mm/hugepage_settings.h
+++ b/tools/lib/mm/hugepage_settings.h
@@ -83,6 +83,8 @@ static inline void thp_save_settings(void)
 	hugepage_save_settings(/* thp = */ true, /* hugetlb = */ false);
 }
 
+bool khugepaged_full_pass(unsigned int timeout_s);
+
 void thp_set_read_ahead_path(char *path);
 unsigned long thp_supported_orders(void);
 unsigned long thp_shmem_supported_orders(void);
-- 
2.54.0

[PATCH v6 11/19] selftests/mm: add order-parameterized khugepaged collapse cases

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The mthp_khugepaged context runs the generic cases at a sub-PMD order,
which answers how many folios of that order a range ends up with.  It
cannot say which order-sized window they landed in, so "the populated
window collapsed" and "the empty window next to it collapsed instead" look
alike.

Add four cases that check each window on its own, with the folio-order
helpers in vm_util:

- collapse_order_single_window(): only the populated window collapses;
- collapse_order_partial_window(): the default max_ptes_none lets a window
  with one present PTE collapse;
- collapse_order_max_ptes_none(): with max_ptes_none=0 a full window
  collapses and one missing a page does not;
- collapse_order_mixed_sources(): sources that are already large folios of
  a smaller order collapse to the target.

Each case faults its region before MADV_HUGEPAGE with only the target
order enabled, so the sources are order 0 and the result can only come
from khugepaged.  They wait for a full pass rather than for the result to
appear: without a completed pass, "not collapsed" and "not scanned yet"
are the same thing.

Assisted-by: LLM
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 212 ++++++++++++++++++++++++
 1 file changed, 212 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index e013eebc7136..51bda01446cd 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -30,6 +30,8 @@ static unsigned long page_size;
 static int hpage_pmd_nr;
 static int anon_order;
 static int collapse_order;
+static int pagemap_fd = -1;
+static int kpageflags_fd = -1;
 
 #define PID_SMAPS "/proc/self/smaps"
 #define TEST_FILE "collapse_test_file"
@@ -1209,6 +1211,198 @@ static void madvise_retracted_page_tables(struct collapse_context *c,
 	ksft_test_result_report(exit_status, "%s\n", __func__);
 }
 
+/* Smallest order khugepaged will consider for mTHP collapse */
+#define MIN_MTHP_ORDER 2
+
+/* Time budget for one khugepaged pass in the collapse_order_* cases */
+#define MTHP_PASS_TIMEOUT_S 30
+
+static size_t mthp_window_size(void)
+{
+	return page_size << collapse_order;
+}
+
+static void mthp_push_target_order(void)
+{
+	struct thp_settings settings = *thp_current_settings();
+	int i;
+
+	/*
+	 * Only the target order, and only for madvise: the cases fault their
+	 * region first, so the sources stay order 0 whatever -s asked for.
+	 */
+	settings.thp_enabled = THP_NEVER;
+	for (i = 0; i < NR_ORDERS; i++)
+		settings.hugepages[i].enabled = THP_NEVER;
+	settings.hugepages[collapse_order].enabled = THP_MADVISE;
+	thp_push_settings(&settings);
+}
+
+static bool all_windows_at_order(void *p, size_t len)
+{
+	return is_range_backed_by_order(p, len, collapse_order,
+					pagemap_fd, kpageflags_fd);
+}
+
+static bool any_window_at_order(void *p, size_t len)
+{
+	size_t window = mthp_window_size();
+	char *addr = p;
+
+	for (; len >= window; addr += window, len -= window) {
+		if (all_windows_at_order(addr, window))
+			return true;
+	}
+	return false;
+}
+
+static void collapse_order_single_window(struct collapse_context *c,
+					 struct mem_ops *ops)
+{
+	size_t window = mthp_window_size();
+	void *p;
+
+	mthp_push_target_order();
+
+	p = ops->setup_area(1);
+	ops->fault(p, window, 2 * window);
+	if (any_window_at_order(p, hpage_pmd_size))
+		ksft_exit_fail_msg("Unexpected large folio after fault\n");
+
+	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
+		ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
+	ksft_print_msg("Collapse one fully populated window...");
+	if (!khugepaged_full_pass(MTHP_PASS_TIMEOUT_S))
+		fail("Timeout");
+	else if (all_windows_at_order(p + window, window) &&
+		 !any_window_at_order(p, window) &&
+		 !any_window_at_order(p + 2 * window,
+				      hpage_pmd_size - 2 * window))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, window, 2 * window);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
+static void collapse_order_partial_window(struct collapse_context *c,
+					  struct mem_ops *ops)
+{
+	void *p;
+
+	mthp_push_target_order();
+
+	p = ops->setup_area(1);
+	ops->fault(p, 0, page_size);
+	if (any_window_at_order(p, hpage_pmd_size))
+		ksft_exit_fail_msg("Unexpected large folio after fault\n");
+
+	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
+		ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
+	ksft_print_msg("Collapse window with single PTE entry present...");
+	if (!khugepaged_full_pass(MTHP_PASS_TIMEOUT_S))
+		fail("Timeout");
+	else if (all_windows_at_order(p, mthp_window_size()))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, 0, page_size);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
+static void collapse_order_max_ptes_none(struct collapse_context *c,
+					 struct mem_ops *ops)
+{
+	struct thp_settings settings;
+	size_t window = mthp_window_size();
+	void *p;
+
+	mthp_push_target_order();
+	settings = *thp_current_settings();
+	settings.khugepaged.max_ptes_none = 0;
+	thp_push_settings(&settings);
+
+	p = ops->setup_area(1);
+	ops->fault(p, 0, 2 * window - page_size);
+	if (any_window_at_order(p, hpage_pmd_size))
+		ksft_exit_fail_msg("Unexpected large folio after fault\n");
+
+	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
+		ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
+	ksft_print_msg("Collapse full window, not the one missing a page...");
+	if (!khugepaged_full_pass(MTHP_PASS_TIMEOUT_S))
+		fail("Timeout");
+	else if (all_windows_at_order(p, window) &&
+		 !any_window_at_order(p + window, window))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, 0, 2 * window - page_size);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
+static void collapse_order_mixed_sources(struct collapse_context *c,
+					 struct mem_ops *ops)
+{
+	struct thp_settings settings;
+	void *p;
+
+	if (collapse_order <= MIN_MTHP_ORDER) {
+		ksft_test_result_skip("%s: no source order below target\n",
+				      __func__);
+		return;
+	}
+
+	mthp_push_target_order();
+
+	settings = *thp_current_settings();
+	settings.hugepages[MIN_MTHP_ORDER].enabled = THP_ALWAYS;
+	thp_push_settings(&settings);
+	p = ops->setup_area(1);
+	ops->fault(p, 0, hpage_pmd_size);
+	thp_pop_settings();
+
+	/*
+	 * The allocator can fall back to smaller folios under fragmentation;
+	 * having nothing to collapse from is not a failure.
+	 */
+	if (!is_range_backed_by_order(p, hpage_pmd_size, MIN_MTHP_ORDER,
+				      pagemap_fd, kpageflags_fd)) {
+		ksft_print_msg("No order-%d sources to collapse...",
+			       MIN_MTHP_ORDER);
+		skip("Skip");
+		ops->cleanup_area(p, hpage_pmd_size);
+		thp_pop_settings();
+		ksft_test_result_report(exit_status, "%s\n", __func__);
+		return;
+	}
+
+	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
+		ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
+	ksft_print_msg("Collapse region backed by smaller large folios...");
+	if (!khugepaged_full_pass(MTHP_PASS_TIMEOUT_S))
+		fail("Timeout");
+	else if (all_windows_at_order(p, hpage_pmd_size))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, 0, hpage_pmd_size);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
 static void usage(void)
 {
 	fprintf(stderr, "\nUsage: ./khugepaged [OPTIONS] <test type> [dir]\n\n");
@@ -1377,6 +1571,20 @@ int main(int argc, char **argv)
 
 	parse_test_type(argc, argv);
 
+	if (mthp_khugepaged_context &&
+	    !(thp_supported_orders() & (1UL << collapse_order)))
+		ksft_exit_skip("Order %d is not a supported anon THP order\n",
+			       collapse_order);
+
+	if (mthp_khugepaged_context) {
+		pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+		if (pagemap_fd < 0)
+			ksft_exit_fail_perror("open(/proc/self/pagemap)");
+		kpageflags_fd = open("/proc/kpageflags", O_RDONLY);
+		if (kpageflags_fd < 0)
+			ksft_exit_fail_perror("open(/proc/kpageflags)");
+	}
+
 	setbuf(stdout, NULL);
 
 	/*
@@ -1427,6 +1635,10 @@ int main(int argc, char **argv)
 	TEST(collapse_empty, madvise_context, anon_ops);
 
 	TEST(collapse_single_mthp, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_single_window, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_partial_window, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_max_ptes_none, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_mixed_sources, mthp_khugepaged_context, anon_ops);
 
 	TEST(collapse_single_pte_entry, khugepaged_context, anon_ops);
 	TEST(collapse_single_pte_entry, khugepaged_context, read_only_file_ops);
-- 
2.54.0

[PATCH v6 12/19] selftests/mm: parameterize the mixed-source collapse case by source order

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

collapse_order_mixed_sources() faults its region as order-2 folios and
collapses them to the -c target.  Order 2 is below the contpte size on
every arm64 page size, so nothing in this suite collapses a contpte-mapped
source on purpose.

Let -s name the source order alongside -c.  The case then faults at that
order, keeping order 2 when -s is absent, and the source order has to be a
supported mTHP order below the target.  The other mTHP cases are
unaffected: mthp_push_target_order() enables only the target order.

A -c at or below -s is refused before any case runs: the sources would
already be the size being asked for.  Without the check the generic cases
fail on that one by one instead of saying why.

"-s 5 -c 7" on arm64/64K then collapses contpte-mapped sources into a
larger mTHP.

Assisted-by: LLM
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 51bda01446cd..9d1c47bd5013 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1354,11 +1354,13 @@ static void collapse_order_max_ptes_none(struct collapse_context *c,
 static void collapse_order_mixed_sources(struct collapse_context *c,
 					 struct mem_ops *ops)
 {
+	int source_order = anon_order ? anon_order : MIN_MTHP_ORDER;
 	struct thp_settings settings;
 	void *p;
 
-	if (collapse_order <= MIN_MTHP_ORDER) {
-		ksft_test_result_skip("%s: no source order below target\n",
+	if (source_order >= collapse_order ||
+	    !(thp_supported_orders() & (1UL << source_order))) {
+		ksft_test_result_skip("%s: no supported source order below target\n",
 				      __func__);
 		return;
 	}
@@ -1366,7 +1368,7 @@ static void collapse_order_mixed_sources(struct collapse_context *c,
 	mthp_push_target_order();
 
 	settings = *thp_current_settings();
-	settings.hugepages[MIN_MTHP_ORDER].enabled = THP_ALWAYS;
+	settings.hugepages[source_order].enabled = THP_ALWAYS;
 	thp_push_settings(&settings);
 	p = ops->setup_area(1);
 	ops->fault(p, 0, hpage_pmd_size);
@@ -1376,10 +1378,9 @@ static void collapse_order_mixed_sources(struct collapse_context *c,
 	 * The allocator can fall back to smaller folios under fragmentation;
 	 * having nothing to collapse from is not a failure.
 	 */
-	if (!is_range_backed_by_order(p, hpage_pmd_size, MIN_MTHP_ORDER,
+	if (!is_range_backed_by_order(p, hpage_pmd_size, source_order,
 				      pagemap_fd, kpageflags_fd)) {
-		ksft_print_msg("No order-%d sources to collapse...",
-			       MIN_MTHP_ORDER);
+		ksft_print_msg("No order-%d sources to collapse...", source_order);
 		skip("Skip");
 		ops->cleanup_area(p, hpage_pmd_size);
 		thp_pop_settings();
@@ -1389,7 +1390,8 @@ static void collapse_order_mixed_sources(struct collapse_context *c,
 
 	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
 		ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
-	ksft_print_msg("Collapse region backed by smaller large folios...");
+	ksft_print_msg("Collapse region backed by order-%d sources...",
+		       source_order);
 	if (!khugepaged_full_pass(MTHP_PASS_TIMEOUT_S))
 		fail("Timeout");
 	else if (all_windows_at_order(p, hpage_pmd_size))
@@ -1420,6 +1422,7 @@ static void usage(void)
 	fprintf(stderr,	"\t\t-s: mTHP size, expressed as page order.\n");
 	fprintf(stderr,	"\t\t    Defaults to 0. Use this size for anon or shmem allocations.\n");
 	fprintf(stderr,	"\t\t-c: collapse order for mTHP collapse, expressed as page order.\n");
+	fprintf(stderr,	"\t\t    -s, if set, is the source order for the mixed-source case.\n");
 	exit(1);
 }
 
@@ -1575,6 +1578,9 @@ int main(int argc, char **argv)
 	    !(thp_supported_orders() & (1UL << collapse_order)))
 		ksft_exit_skip("Order %d is not a supported anon THP order\n",
 			       collapse_order);
+	if (mthp_khugepaged_context && collapse_order <= anon_order)
+		ksft_exit_skip("-c %d needs a source order below it, -s says %d\n",
+			       collapse_order, anon_order);
 
 	if (mthp_khugepaged_context) {
 		pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
-- 
2.54.0

[PATCH v6 13/19] selftests/mm: cover a shared-source collapse write race

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

collapse_fork() checks that a fork-shared range collapses in the child
while the parent keeps its own pages, but the parent sits still while
that happens.  Nothing checks that CoW isolation survives a collapse
racing with writes to the shared source.

Add a case where the parent writes to the shared range throughout the
child's collapse.  CoW has to keep the two apart: the child must see the
content from before the fork, and the parent only its own writes.

The parent unshares one page every 10ms, starting only once the child
says it is about to collapse.  Writing the range in a burst would break
CoW on all of it before the collapse begins, leaving the child to collapse
pages that are already exclusive to it.

Preparation for changing how collapse handles fork-shared sources.

Assisted-by: LLM
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c | 106 ++++++++++++++++++++++++
 1 file changed, 106 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 9d1c47bd5013..21ae258bd56e 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1166,6 +1166,109 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
 	ksft_test_result_report(exit_status, "%s\n", __func__);
 }
 
+/*
+ * The parent writes to the fork-shared range throughout the child's
+ * collapse.  CoW must keep the two apart: the child sees the pre-fork
+ * content, the parent only its own writes.
+ */
+static void collapse_fork_cow_race(struct collapse_context *c, struct mem_ops *ops)
+{
+	const int stride = page_size / sizeof(int);
+	int wstatus, child_status, i, n;
+	unsigned long shared;
+	volatile int *ip;
+	pid_t child;
+	int sync[2];
+	char go = 1;
+	void *p;
+
+	/* At a page per 10 ms, 64 pages spread the writes across the collapse */
+	n = 64;
+	shared = n * page_size;
+
+	p = ops->setup_area(1);
+	/* Shared prefix, with the pre-fork pattern */
+	ops->fault(p, 0, shared);
+	if (pipe(sync))
+		ksft_exit_fail_perror("pipe()");
+
+	/* A volatile pointer so the stores are not merged or dropped */
+	ip = p;
+
+	ksft_print_msg("Fork, collapse in the child while the parent rewrites...");
+	child = fork();
+	if (!child) {
+		int collapse_status;
+
+		close(sync[0]);
+		/* Private remainder */
+		ops->fault(p, shared, hpage_pmd_size);
+		/* Start the parent unsharing, and give it a head start */
+		if (write(sync[1], &go, 1) != 1)
+			_exit(KSFT_FAIL);
+		usleep(5000);
+		c->collapse("Collapse a range the parent is writing to",
+			    p, 1, ops, true);
+		collapse_status = exit_status;
+		for (i = 0; i < n; i++)
+			if (ip[i * stride] != i + 0xdead0000)
+				break;
+		if (i == n)
+			success("OK");
+		else
+			fail("Fail: child content");
+		/* The content check must not bury a failed collapse */
+		if (exit_status != KSFT_FAIL)
+			exit_status = collapse_status;
+		ops->cleanup_area(p, hpage_pmd_size);
+		_exit(exit_status);
+	}
+
+	close(sync[1]);
+	if (read(sync[0], &go, 1) != 1)
+		ksft_exit_fail_msg("child never reached the collapse\n");
+	close(sync[0]);
+
+	/*
+	 * Unshare one page at a time: a burst would break CoW on the whole
+	 * range before the collapse starts, leaving nothing shared to collapse.
+	 */
+	i = 0;
+	for (;;) {
+		pid_t ret;
+
+		if (i < n)
+			ip[i * stride] = i + 0xbeef0000;
+		i++;
+		usleep(10 * 1000);
+		ret = waitpid(child, &wstatus, WNOHANG);
+		if (ret == child)
+			break;
+		if (ret < 0)
+			ksft_exit_fail_perror("waitpid()");
+	}
+
+	/* Finish whatever the paced sweep did not reach */
+	for (; i < n; i++)
+		ip[i * stride] = i + 0xbeef0000;
+	/* A child that died reading the racing pages is a failure, not a zero */
+	child_status = WIFEXITED(wstatus) ? WEXITSTATUS(wstatus) : KSFT_FAIL;
+
+	ksft_print_msg("Check the parent sees only its own writes...");
+	for (i = 0; i < n; i++)
+		if (ip[i * stride] != i + 0xbeef0000)
+			break;
+	if (i == n)
+		success("OK");
+	else
+		fail("Fail: parent content");
+	ops->cleanup_area(p, hpage_pmd_size);
+	/* The parent's check must not bury the child's verdict */
+	if (exit_status != KSFT_FAIL)
+		exit_status = child_status;
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
 static void madvise_collapse_existing_thps(struct collapse_context *c,
 					   struct mem_ops *ops)
 {
@@ -1700,6 +1803,9 @@ int main(int argc, char **argv)
 	TEST(collapse_max_ptes_shared, khugepaged_context, anon_ops);
 	TEST(collapse_max_ptes_shared, madvise_context, anon_ops);
 
+	TEST(collapse_fork_cow_race, khugepaged_context, anon_ops);
+	TEST(collapse_fork_cow_race, madvise_context, anon_ops);
+
 	TEST(madvise_collapse_existing_thps, madvise_context, anon_ops);
 	TEST(madvise_collapse_existing_thps, madvise_context, read_only_file_ops);
 	TEST(madvise_collapse_existing_thps, madvise_context, read_write_file_read_ops);
-- 
2.54.0

[PATCH v6 14/19] selftests/mm: run every supported collapse order by default

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The mTHP collapse cases only run when the caller names both the context
and an order, so a plain ./khugepaged covers the PMD contexts on anon and
nothing else.  run_vmtests.sh pinned order 4 and covered no other.

Run the mTHP cases once per supported anon THP order below the PMD when
-c is absent, and pull that context into both the no-argument invocation
and "all".  Also:

  - -c still pins one order, and now says what is wrong instead of
    printing the usage text.

  - Both orders end up as array indices and shift counts, so -s and -c
    are range-checked before they get there.

  - The mTHP context has only anon cases, so a run that names a different
    mem_type -- "all:shmem", say -- drops it again rather than refusing
    to start.  Naming both explicitly still refuses.

  - A case carries the order it was registered at, so a result names it:

      # Run test: collapse_single_mthp (mthp_khugepaged:anon, order 6)

On x86-64 with 4K pages that is orders 2 through 8, and ./khugepaged goes
from 29 results in 17 seconds to 77 in 29, so run_vmtests.sh can drop its
pinned order-4 line.

Assisted-by: LLM
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged.c   | 101 +++++++++++++++++-----
 tools/testing/selftests/mm/run_vmtests.sh |   2 -
 2 files changed, 78 insertions(+), 25 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 21ae258bd56e..a2ac3b3ca5de 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -30,6 +30,9 @@ static unsigned long page_size;
 static int hpage_pmd_nr;
 static int anon_order;
 static int collapse_order;
+static bool collapse_order_set;
+static int collapse_orders[NR_ORDERS];
+static int nr_collapse_orders;
 static int pagemap_fd = -1;
 static int kpageflags_fd = -1;
 
@@ -1525,12 +1528,14 @@ static void usage(void)
 	fprintf(stderr,	"\t\t-s: mTHP size, expressed as page order.\n");
 	fprintf(stderr,	"\t\t    Defaults to 0. Use this size for anon or shmem allocations.\n");
 	fprintf(stderr,	"\t\t-c: collapse order for mTHP collapse, expressed as page order.\n");
+	fprintf(stderr,	"\t\t    Defaults to every supported order below the PMD.\n");
 	fprintf(stderr,	"\t\t    -s, if set, is the source order for the mixed-source case.\n");
 	exit(1);
 }
 
 static void parse_test_type(int argc, char **argv)
 {
+	bool mthp_context_implied = false;
 	int opt;
 	char *buf;
 	const char *token;
@@ -1542,6 +1547,7 @@ static void parse_test_type(int argc, char **argv)
 			break;
 		case 'c':
 			collapse_order = atoi(optarg);
+			collapse_order_set = true;
 			break;
 		case 'h':
 		default:
@@ -1549,12 +1555,25 @@ static void parse_test_type(int argc, char **argv)
 		}
 	}
 
+	/*
+	 * Both orders end up as array indices and shift counts, so neither
+	 * can be negative, and a zero collapse order asks for base pages.
+	 */
+	if (anon_order < 0 || anon_order > hpage_pmd_order)
+		ksft_exit_fail_msg("-s takes an order in 0..%d, not %d\n",
+				   hpage_pmd_order, anon_order);
+	if (collapse_order_set &&
+	    (collapse_order <= 0 || collapse_order >= hpage_pmd_order))
+		ksft_exit_fail_msg("-c takes an order in 1..%d, not %d\n",
+				   hpage_pmd_order - 1, collapse_order);
+
 	argv += optind;
 	argc -= optind;
 
 	if (argc == 0) {
-		/* Backwards compatibility */
+		/* No arguments: anon under every context */
 		khugepaged_context =  &__khugepaged_context;
+		mthp_khugepaged_context =  &__mthp_khugepaged_context;
 		madvise_context =  &__madvise_context;
 		anon_ops = &__anon_ops;
 		return;
@@ -1565,13 +1584,14 @@ static void parse_test_type(int argc, char **argv)
 
 	if (!strcmp(token, "all")) {
 		khugepaged_context =  &__khugepaged_context;
+		mthp_khugepaged_context =  &__mthp_khugepaged_context;
 		madvise_context =  &__madvise_context;
+		/* The mTHP context has only anon cases; let other mem_types drop it */
+		mthp_context_implied = true;
 	} else if (!strcmp(token, "khugepaged")) {
 		khugepaged_context =  &__khugepaged_context;
 	} else if (!strcmp(token, "mthp_khugepaged")) {
 		mthp_khugepaged_context =  &__mthp_khugepaged_context;
-		if (collapse_order <= 0 || collapse_order >= hpage_pmd_order)
-			usage();
 	} else if (!strcmp(token, "madvise")) {
 		madvise_context =  &__madvise_context;
 	} else {
@@ -1587,20 +1607,20 @@ static void parse_test_type(int argc, char **argv)
 		read_write_file_write_ops =  &__read_write_file_write_ops;
 		anon_ops = &__anon_ops;
 		shmem_ops = &__shmem_ops;
-		if (mthp_khugepaged_context)
-			usage();
 	} else if (!strcmp(buf, "anon")) {
 		anon_ops = &__anon_ops;
 	} else if (!strcmp(buf, "file")) {
 		read_only_file_ops =  &__read_only_file_ops;
 		read_write_file_read_ops =  &__read_write_file_read_ops;
 		read_write_file_write_ops =  &__read_write_file_write_ops;
-		if (mthp_khugepaged_context)
+		if (mthp_khugepaged_context && !mthp_context_implied)
 			usage();
+		mthp_khugepaged_context = NULL;
 	} else if (!strcmp(buf, "shmem")) {
 		shmem_ops = &__shmem_ops;
-		if (mthp_khugepaged_context)
+		if (mthp_khugepaged_context && !mthp_context_implied)
 			usage();
+		mthp_khugepaged_context = NULL;
 	} else {
 		usage();
 	}
@@ -1622,6 +1642,7 @@ struct test_case {
 	struct mem_ops *ops;
 	const char *desc;
 	test_fn fn;
+	int order;		/* mTHP contexts: the collapse order */
 };
 
 #define MAX_TEST_CASES 256
@@ -1637,6 +1658,7 @@ static int nr_test_cases;
 			.ops	= o,					\
 			.desc	= #t,					\
 			.fn	= t,					\
+			.order	= collapse_order,			\
 		};							\
 	}								\
 	} while (0)
@@ -1677,13 +1699,35 @@ int main(int argc, char **argv)
 
 	parse_test_type(argc, argv);
 
-	if (mthp_khugepaged_context &&
-	    !(thp_supported_orders() & (1UL << collapse_order)))
-		ksft_exit_skip("Order %d is not a supported anon THP order\n",
-			       collapse_order);
-	if (mthp_khugepaged_context && collapse_order <= anon_order)
-		ksft_exit_skip("-c %d needs a source order below it, -s says %d\n",
-			       collapse_order, anon_order);
+	if (mthp_khugepaged_context) {
+		unsigned long orders = thp_supported_orders();
+
+		if (collapse_order_set) {
+			if (!(orders & (1UL << collapse_order)))
+				ksft_exit_skip("Order %d is not a supported anon THP order\n",
+					       collapse_order);
+			if (collapse_order <= anon_order)
+				ksft_exit_skip("-c %d needs a source order below it, -s says %d\n",
+					       collapse_order, anon_order);
+			collapse_orders[nr_collapse_orders++] = collapse_order;
+		} else {
+			/*
+			 * Every supported order above the source: -s makes the
+			 * fault path hand out folios of that order, so a target
+			 * at or below it has nothing to collapse.
+			 */
+			int first = anon_order + 1;
+
+			if (first < MIN_MTHP_ORDER)
+				first = MIN_MTHP_ORDER;
+			for (int i = first; i < hpage_pmd_order; i++) {
+				if (orders & (1UL << i))
+					collapse_orders[nr_collapse_orders++] = i;
+			}
+			if (!nr_collapse_orders)
+				ksft_print_msg("mTHP cases skipped: no order above the source\n");
+		}
+	}
 
 	if (mthp_khugepaged_context) {
 		pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
@@ -1732,7 +1776,17 @@ int main(int argc, char **argv)
 	TEST(collapse_full, khugepaged_context, read_write_file_read_ops);
 	TEST(collapse_full, khugepaged_context, read_write_file_write_ops);
 	TEST(collapse_full, khugepaged_context, shmem_ops);
-	TEST(collapse_full, mthp_khugepaged_context, anon_ops);
+	for (int i = 0; i < nr_collapse_orders; i++) {
+		collapse_order = collapse_orders[i];
+		TEST(collapse_full, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_empty, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_single_mthp, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_order_single_window, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_order_partial_window, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_order_max_ptes_none, mthp_khugepaged_context, anon_ops);
+		TEST(collapse_order_mixed_sources, mthp_khugepaged_context, anon_ops);
+	}
+
 	TEST(collapse_full, madvise_context, anon_ops);
 	TEST(collapse_full, madvise_context, read_only_file_ops);
 	TEST(collapse_full, madvise_context, read_write_file_read_ops);
@@ -1740,15 +1794,8 @@ int main(int argc, char **argv)
 	TEST(collapse_full, madvise_context, shmem_ops);
 
 	TEST(collapse_empty, khugepaged_context, anon_ops);
-	TEST(collapse_empty, mthp_khugepaged_context, anon_ops);
 	TEST(collapse_empty, madvise_context, anon_ops);
 
-	TEST(collapse_single_mthp, mthp_khugepaged_context, anon_ops);
-	TEST(collapse_order_single_window, mthp_khugepaged_context, anon_ops);
-	TEST(collapse_order_partial_window, mthp_khugepaged_context, anon_ops);
-	TEST(collapse_order_max_ptes_none, mthp_khugepaged_context, anon_ops);
-	TEST(collapse_order_mixed_sources, mthp_khugepaged_context, anon_ops);
-
 	TEST(collapse_single_pte_entry, khugepaged_context, anon_ops);
 	TEST(collapse_single_pte_entry, khugepaged_context, read_only_file_ops);
 	TEST(collapse_single_pte_entry, khugepaged_context, read_write_file_read_ops);
@@ -1821,7 +1868,15 @@ int main(int argc, char **argv)
 	for (int i = 0; i < nr_test_cases; i++) {
 		struct test_case *t = &test_cases[i];
 
-		ksft_print_msg("\n# Run test: %s (%s:%s)\n", t->desc, t->ctx->name, t->ops->name);
+		if (t->ctx == &__mthp_khugepaged_context) {
+			collapse_order = t->order;
+			ksft_print_msg("\n# Run test: %s (%s:%s, order %d)\n",
+				       t->desc, t->ctx->name, t->ops->name,
+				       t->order);
+		} else {
+			ksft_print_msg("\n# Run test: %s (%s:%s)\n", t->desc,
+				       t->ctx->name, t->ops->name);
+		}
 		t->fn(t->ctx, t->ops);
 	}
 
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 3a111bc9c29e..98a33f6d15d4 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -392,8 +392,6 @@ CATEGORY="thp" run_test ./khugepaged all:shmem
 
 CATEGORY="thp" run_test ./khugepaged -s 4 all:shmem
 
-CATEGORY="thp" run_test ./khugepaged -c 4 mthp_khugepaged:anon
-
 # Try to create XFS if not provided
 if [ -z "${SPLIT_HUGE_PAGE_TEST_XFS_PATH}" ]; then
     if test_selected "thp"; then
-- 
2.54.0

[PATCH v6 15/19] selftests/mm: check that one khugepaged pass collapses one window

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

khugepaged_full_pass() drives the daemon through sysfs: a store to
scan_sleep_millisecs wakes it, and full_scans advancing by two marks one
pass that started after setup.  Every mTHP collapse result in the suite
rests on that pair, and nothing checks it.

Add khugepaged_sync_check.  Each step:

  - prepare one aligned window
  - record its source PFNs from pagemap
  - run one khugepaged_full_pass() barrier
  - require the window came out collapsed, with exactly one collapse
    attempt attributed to it

The anon events carry no virtual address, so an attempt is matched by the
source folio PFN and order that the mm_collapse_huge_page_isolate
tracepoint reports.

Reading the trace buffer takes four small helpers in vm_util: open an
event subsystem's enable file, flip it, clear the buffer, and open it for
reading.

scan_sleep_millisecs is set to a minute, so a step that took a sleep
instead of a wake would blow the budget.

Passes 5/5 on x86-64 4K and arm64 64K.

Assisted-by: LLM
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/Makefile           |   1 +
 .../selftests/mm/khugepaged_sync_check.c      | 179 ++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh     |   2 +
 tools/testing/selftests/mm/vm_util.c          |  38 ++++
 tools/testing/selftests/mm/vm_util.h          |   4 +
 5 files changed, 224 insertions(+)
 create mode 100644 tools/testing/selftests/mm/khugepaged_sync_check.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index cb32cf5d867e..2ed881324911 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -106,6 +106,7 @@ TEST_GEN_FILES += merge
 TEST_GEN_FILES += rmap
 TEST_GEN_FILES += folio_split_race_test
 TEST_GEN_FILES += folio_order_check
+TEST_GEN_FILES += khugepaged_sync_check
 TEST_GEN_FILES += soft-dirty
 
 ifeq ($(ARCH),x86_64)
diff --git a/tools/testing/selftests/mm/khugepaged_sync_check.c b/tools/testing/selftests/mm/khugepaged_sync_check.c
new file mode 100644
index 000000000000..28a9b1ff5d44
--- /dev/null
+++ b/tools/testing/selftests/mm/khugepaged_sync_check.c
@@ -0,0 +1,179 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Check that khugepaged_full_pass() drives khugepaged in step: one barrier
+ * over one prepared window must collapse it with exactly one collapse
+ * attempt attributed to its source pages, step after step.
+ *
+ * scan_sleep_millisecs is a minute so that a step which slept instead of
+ * being woken blows the budget.
+ */
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "kselftest.h"
+#include "vm_util.h"
+#include <mm/hugepage_settings.h>
+
+#define BASE_ADDR ((void *)(1UL << 30))
+/* Smallest order khugepaged considers */
+#define TARGET_ORDER 2
+#define NR_ITERATIONS 5
+#define PASS_TIMEOUT_S 30
+
+static int pagemap_fd;
+static int kpageflags_fd;
+static int trace_events_fd = -1;
+static unsigned long hpage_pmd_size;
+
+/*
+ * The events are system-wide: switch them off however the test ends,
+ * including from inside a helper that gives up.
+ */
+static void trace_events_off(void)
+{
+	if (trace_events_fd >= 0)
+		tracing_events_enable(trace_events_fd, false);
+}
+
+/* Count the isolate events whose scan_pfn is one of the window's source PFNs */
+static int count_attributed(unsigned long *pfns, int nr_pfns,
+			    unsigned int order)
+{
+	char line[1024];
+	int count = 0;
+	FILE *fp;
+
+	fp = tracing_open_trace();
+	if (!fp)
+		ksft_exit_fail_msg("Cannot open trace buffer\n");
+
+	while (fgets(line, sizeof(line), fp)) {
+		unsigned long val;
+		unsigned int ord;
+		char *s, *o;
+		int i;
+
+		s = strstr(line, "mm_collapse_huge_page_isolate:");
+		if (!s)
+			continue;
+		if (sscanf(s, "mm_collapse_huge_page_isolate: scan_pfn=0x%lx",
+			   &val) != 1)
+			continue;
+		o = strstr(s, "order=");
+		if (!o || sscanf(o, "order=%u", &ord) != 1 || ord != order)
+			continue;
+		for (i = 0; i < nr_pfns; i++) {
+			if (val == pfns[i]) {
+				count++;
+				break;
+			}
+		}
+	}
+	fclose(fp);
+	return count;
+}
+
+static void one_step(int iteration)
+{
+	const size_t window = getpagesize() << TARGET_ORDER;
+	const int nr_pages = 1 << TARGET_ORDER;
+	unsigned long pfns[1 << TARGET_ORDER];
+	bool collapsed, passed;
+	int attributed;
+	char *p;
+	int i;
+
+	p = mmap(BASE_ADDR, hpage_pmd_size, PROT_READ | PROT_WRITE,
+		 MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE, -1, 0);
+	if (p != BASE_ADDR)
+		ksft_exit_fail_perror("mmap() window");
+
+	for (i = 0; i < nr_pages; i++) {
+		p[i * getpagesize()] = i + 1;
+		pfns[i] = pagemap_get_pfn(pagemap_fd, p + i * getpagesize());
+		if (pfns[i] == -1UL)
+			ksft_exit_fail_msg("Source page not present\n");
+	}
+
+	/* Clear before enabling so the buffer holds only this step's events */
+	if (tracing_clear_trace())
+		ksft_exit_fail_msg("Cannot clear the trace buffer\n");
+	if (tracing_events_enable(trace_events_fd, true))
+		ksft_exit_fail_msg("Cannot enable huge_memory events\n");
+
+	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
+		ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
+	passed = khugepaged_full_pass(PASS_TIMEOUT_S);
+
+	/* Off before anything that can give up: the events are system-wide */
+	if (tracing_events_enable(trace_events_fd, false))
+		ksft_exit_fail_msg("Cannot disable huge_memory events\n");
+	if (!passed)
+		ksft_exit_fail_msg("khugepaged did not complete a full pass\n");
+
+	collapsed = is_range_backed_by_order(p, window, TARGET_ORDER,
+					     pagemap_fd, kpageflags_fd);
+	attributed = count_attributed(pfns, nr_pages, TARGET_ORDER);
+
+	ksft_test_result(collapsed && attributed == 1,
+			 "step %d: window collapsed, %d attributed result(s)\n",
+			 iteration, attributed);
+
+	munmap(p, hpage_pmd_size);
+}
+
+int main(void)
+{
+	struct thp_settings settings;
+	int i;
+
+	ksft_print_header();
+
+	if (!thp_available())
+		ksft_exit_skip("Transparent Hugepages not available\n");
+	if (!(thp_supported_orders() & (1UL << TARGET_ORDER)))
+		ksft_exit_skip("Order %d is not a supported anon THP order\n",
+			       TARGET_ORDER);
+
+	hpage_pmd_size = read_pmd_pagesize();
+	if (!hpage_pmd_size)
+		ksft_exit_fail_msg("Reading PMD pagesize failed\n");
+	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	if (pagemap_fd < 0)
+		ksft_exit_fail_perror("open(/proc/self/pagemap)");
+	kpageflags_fd = open("/proc/kpageflags", O_RDONLY);
+	if (kpageflags_fd < 0)
+		ksft_exit_skip("open(/proc/kpageflags) requires root\n");
+	trace_events_fd = tracing_events_open("huge_memory");
+	if (trace_events_fd < 0)
+		ksft_exit_skip("huge_memory events require tracefs and root\n");
+	atexit(trace_events_off);
+
+	ksft_set_plan(NR_ITERATIONS);
+
+	thp_save_settings();
+	thp_read_settings(&settings);
+	settings.thp_enabled = THP_MADVISE;
+	settings.thp_defrag = THP_DEFRAG_ALWAYS;
+	settings.khugepaged.defrag = 1;
+	settings.khugepaged.scan_sleep_millisecs = 60 * 1000;
+	settings.khugepaged.alloc_sleep_millisecs = 60 * 1000;
+	settings.khugepaged.max_ptes_none = (hpage_pmd_size / getpagesize()) - 1;
+	/* One wake must complete one full pass; see khugepaged_full_pass() */
+	settings.khugepaged.pages_to_scan = 1UL << 24;
+	for (i = 0; i < NR_ORDERS; i++)
+		settings.hugepages[i].enabled = THP_NEVER;
+	settings.hugepages[TARGET_ORDER].enabled = THP_INHERIT;
+	/* Base of the settings stack; the bottom entry is never popped */
+	thp_push_settings(&settings);
+
+	for (i = 0; i < NR_ITERATIONS; i++)
+		one_step(i);
+
+	ksft_finished();
+}
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 98a33f6d15d4..612a8c4afc53 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -384,6 +384,8 @@ CATEGORY="cow" run_test ./cow
 
 CATEGORY="thp" run_test ./folio_order_check
 
+CATEGORY="thp" run_test ./khugepaged_sync_check
+
 CATEGORY="thp" run_test ./khugepaged
 
 CATEGORY="thp" run_test ./khugepaged -s 2
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index c8c5cd8ab6c1..31d331c1c452 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -602,6 +602,44 @@ bool is_range_backed_by_order(char *start, size_t len, int order,
 	return true;
 }
 
+#define TRACEFS_ROOT "/sys/kernel/tracing"
+
+/*
+ * Returns -1 without tracefs or the subsystem.  The events are system-wide:
+ * whoever switches them on has to switch them off again, on every exit path.
+ */
+int tracing_events_open(const char *subsys)
+{
+	char path[256];
+
+	snprintf(path, sizeof(path), TRACEFS_ROOT "/events/%s/enable",
+		 subsys);
+	return open(path, O_WRONLY);
+}
+
+int tracing_events_enable(int fd, bool enable)
+{
+	if (pwrite(fd, enable ? "1" : "0", 1, 0) != 1)
+		return -1;
+	return 0;
+}
+
+/* Drop what the trace buffer holds so far */
+int tracing_clear_trace(void)
+{
+	int fd = open(TRACEFS_ROOT "/trace", O_WRONLY | O_TRUNC);
+
+	if (fd < 0)
+		return -1;
+	close(fd);
+	return 0;
+}
+
+FILE *tracing_open_trace(void)
+{
+	return fopen(TRACEFS_ROOT "/trace", "r");
+}
+
 /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls)
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index ea48e6a7527e..072a6c756c51 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -121,6 +121,10 @@ int close_procmap(struct procmap_fd *procmap);
 int write_sysfs(const char *file_path, unsigned long val);
 int read_sysfs(const char *file_path, unsigned long *val);
 bool softdirty_supported(void);
+int tracing_events_open(const char *subsys);
+int tracing_events_enable(int fd, bool enable);
+int tracing_clear_trace(void);
+FILE *tracing_open_trace(void);
 
 static inline int open_self_procmap(struct procmap_fd *procmap_out)
 {
-- 
2.54.0

[PATCH v6 16/19] selftests/mm: add khugepaged race harness

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

Collapse serialises against faults, GUP, fork, mremap and zapping through
a protocol of locks, TLB flushes and refcount checks.  No khugepaged
selftest exercises any of it under contention.

Add khugepaged_race.  Six racing threads work the same address space:

  - two faulters
  - an MADV_DONTNEED thread
  - a transient FOLL_PIN thread (gup_test)
  - a forker
  - an mremap thread

One of three drivers collapses under them:

  stepped   khugepaged, one full pass at a time via
            khugepaged_full_pass(), so each step covers a known extent;
  free      khugepaged left to run (scan_sleep_millisecs=0), for soak;
  madvise   an MADV_COLLAPSE and MADV_DONTNEED loop.

Every mode runs in turn unless -m names one, five seconds each.  Every
supported anon THP order is set to inherit and max_ptes_none is 0, so a
window collapses only once fully populated and the racing MADV_DONTNEED
steers selection across orders.

The rule is that a racing page reads as its pattern or as zero, never
anything else.  The faulters and fork children check it throughout, and a
final sweep checks it again.  The other half of the check is the kernel's
own assertions, so read dmesg too.

The pin thread goes through gup_test, so the harness skips without
CONFIG_GUP_TEST or root.  The default playground is three shared PMD-sized
areas plus the mremap thread's, over two gigabytes at a 512M PMD; -a
shrinks it.

Assisted-by: LLM
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/Makefile          |   1 +
 tools/testing/selftests/mm/khugepaged_race.c | 415 +++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh    |   2 +
 3 files changed, 418 insertions(+)
 create mode 100644 tools/testing/selftests/mm/khugepaged_race.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 2ed881324911..beacc0f87304 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -107,6 +107,7 @@ TEST_GEN_FILES += rmap
 TEST_GEN_FILES += folio_split_race_test
 TEST_GEN_FILES += folio_order_check
 TEST_GEN_FILES += khugepaged_sync_check
+TEST_GEN_FILES += khugepaged_race
 TEST_GEN_FILES += soft-dirty
 
 ifeq ($(ARCH),x86_64)
diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c
new file mode 100644
index 000000000000..66c9e2c10f66
--- /dev/null
+++ b/tools/testing/selftests/mm/khugepaged_race.c
@@ -0,0 +1,415 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Race collapse against faults, GUP pins, fork, mremap and MADV_DONTNEED
+ * over the same ranges.  A racing page must read as its pattern or as
+ * zero, never anything else; the kernel's own assertions in dmesg are the
+ * other half of the check.
+ */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/time.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "kselftest.h"
+#include "vm_util.h"
+#include <mm/hugepage_settings.h>
+#include "../../../../mm/gup_test.h"
+
+#ifndef FOLL_WRITE
+#define FOLL_WRITE 0x01
+#endif
+
+#define BASE_ADDR	((void *)(1UL << 30))
+#define PASS_TIMEOUT_S	30
+
+/*
+ * PMD-sized areas the racing threads share, plus one for the mremap
+ * thread.  -a shrinks it where a PMD is 512M.
+ */
+#define DEFAULT_SHARED_AREAS	3
+static int nr_shared_areas;
+static int nr_areas;
+
+static unsigned long hpage_pmd_size;
+static unsigned long page_size;
+/* nr_areas PMD-sized areas; the last one belongs to the mremap thread */
+static char *region;
+static char *mremap_area;
+static char *mremap_scratch;
+static int gup_fd = -1;
+static volatile int stop;
+static volatile int corrupted;
+
+static unsigned int pattern(unsigned long page_idx)
+{
+	unsigned int val = (unsigned int)page_idx * 2654435761U;
+
+	return val ? val : 1;	/* never collides with the zero-fill */
+}
+
+/* Zero means never written; anything else must be this page's pattern */
+static bool page_is_corrupt(unsigned long page_idx, unsigned int *val)
+{
+	*val = *(unsigned int *)(region + page_idx * page_size);
+
+	return *val && *val != pattern(page_idx);
+}
+
+static void check_page(unsigned long page_idx)
+{
+	unsigned int val;
+
+	if (page_is_corrupt(page_idx, &val)) {
+		corrupted = 1;
+		ksft_print_msg("Corruption at page %lu: %#x != %#x\n",
+			       page_idx, val, pattern(page_idx));
+	}
+}
+
+static unsigned long shared_pages(void)
+{
+	return nr_shared_areas * hpage_pmd_size / page_size;
+}
+
+static unsigned long rand_page(unsigned int *seed)
+{
+	return (unsigned long)rand_r(seed) % shared_pages();
+}
+
+/* Clamp so a range never reaches the mremap thread's area */
+static unsigned long room_from(unsigned long page_idx, unsigned long want)
+{
+	unsigned long left = shared_pages() - page_idx;
+
+	return want < left ? want : left;
+}
+
+static void *faulter_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		unsigned long page_idx = rand_page(&seed);
+
+		if (rand_r(&seed) & 1)
+			*(unsigned int *)(region + page_idx * page_size) =
+				pattern(page_idx);
+		else
+			check_page(page_idx);
+	}
+	return NULL;
+}
+
+static void *dontneed_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		unsigned long page_idx = rand_page(&seed);
+		unsigned long nr = 1UL << (rand_r(&seed) % 6);	/* 1..32 pages */
+
+		madvise(region + page_idx * page_size,
+			room_from(page_idx, nr) * page_size, MADV_DONTNEED);
+		usleep(rand_r(&seed) % 500);
+	}
+	return NULL;
+}
+
+static void *pinner_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		struct gup_test gup = {};
+		unsigned long page_idx = rand_page(&seed);
+		unsigned long nr = room_from(page_idx, 16);
+
+		gup.addr = (unsigned long)(region + page_idx * page_size);
+		gup.size = nr * page_size;
+		gup.nr_pages_per_call = nr;
+		gup.gup_flags = FOLL_WRITE;
+		/* Racing MADV_DONTNEED makes transient failures expected */
+		ioctl(gup_fd, PIN_FAST_BENCHMARK, &gup);
+		usleep(rand_r(&seed) % 200);
+	}
+	return NULL;
+}
+
+static void *forker_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		pid_t pid = fork();
+
+		if (pid == 0) {
+			unsigned int val;
+			int bad = 0;
+
+			/*
+			 * No stdio in the child: a thread may hold stdout's
+			 * lock across the fork, and printing under it hangs.
+			 */
+			for (int i = 0; i < 16; i++)
+				bad |= page_is_corrupt(rand_page(&seed), &val);
+			_exit(bad);
+		}
+		if (pid > 0) {
+			int wstatus;
+
+			if (waitpid(pid, &wstatus, 0) < 0)
+				ksft_exit_fail_perror("waitpid()");
+			/* A child killed on the read counts too */
+			if (!WIFEXITED(wstatus) || WEXITSTATUS(wstatus))
+				corrupted = 1;
+		}
+		usleep(rand_r(&seed) % 2000);
+	}
+	return NULL;
+}
+
+static void *mremapper_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+
+	while (!stop) {
+		void *p;
+
+		p = mremap(mremap_area, hpage_pmd_size, hpage_pmd_size,
+			   MREMAP_MAYMOVE | MREMAP_FIXED, mremap_scratch);
+		if (p == MAP_FAILED)
+			ksft_exit_fail_perror("mremap() away");
+		for (int i = 0; i < 8; i++)
+			mremap_scratch[(rand_r(&seed) %
+				(hpage_pmd_size / page_size)) * page_size] = 1;
+		p = mremap(mremap_scratch, hpage_pmd_size, hpage_pmd_size,
+			   MREMAP_MAYMOVE | MREMAP_FIXED, mremap_area);
+		if (p == MAP_FAILED)
+			ksft_exit_fail_perror("mremap() back");
+		/* The move back unmapped the scratch address: claim it again */
+		if (mmap(mremap_scratch, hpage_pmd_size, PROT_NONE,
+			 MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE,
+			 -1, 0) != (void *)mremap_scratch)
+			ksft_exit_fail_perror("mmap() mremap scratch");
+		usleep(rand_r(&seed) % 2000);
+	}
+	return NULL;
+}
+
+static unsigned long now_ms(void)
+{
+	struct timeval tv;
+
+	gettimeofday(&tv, NULL);
+	return tv.tv_sec * 1000UL + tv.tv_usec / 1000;
+}
+
+static void usage(void)
+{
+	fprintf(stderr,
+		"Usage: khugepaged_race [-d seconds] [-m stepped|free|madvise] [-a areas] [-t mask]\n"
+		"\tWithout -m, every mode runs in turn.\n"
+		"\t-d: seconds per mode (default 5)\n"
+		"\t-a: number of shared PMD-sized playground areas (default 3)\n"
+		"\t-t: bitmask of racing threads to start, for bisecting a failure\n");
+	exit(1);
+}
+
+int main(int argc, char **argv)
+{
+	static const char * const thread_names[] = {
+		"faulter", "faulter2", "dontneed", "pinner", "forker",
+		"mremapper",
+	};
+	void *(*const thread_fns[])(void *) = {
+		faulter_fn, faulter_fn, dontneed_fn, pinner_fn, forker_fn,
+		mremapper_fn,
+	};
+	const int nr_threads = ARRAY_SIZE(thread_names);
+	pthread_t threads[ARRAY_SIZE(thread_names)];
+	static const char * const all_modes[] = { "stepped", "free", "madvise" };
+	const char *one_mode[1];
+	const char * const *modes = all_modes;
+	int nr_modes = ARRAY_SIZE(all_modes);
+	const char *mode_arg = NULL;
+	struct thp_settings settings;
+	unsigned long end_ms;
+	int duration_s = 5;
+	unsigned long thread_mask = ~0UL;
+	int nr_areas_arg = 0;
+	unsigned long i;
+	int steps = 0;
+	int opt;
+
+	while ((opt = getopt(argc, argv, "a:d:m:t:h")) != -1) {
+		switch (opt) {
+		case 'a':
+			nr_areas_arg = atoi(optarg);
+			break;
+		case 'd':
+			duration_s = atoi(optarg);
+			break;
+		case 'm':
+			mode_arg = optarg;
+			break;
+		case 't':
+			thread_mask = strtoul(optarg, NULL, 0);
+			break;
+		default:
+			usage();
+		}
+	}
+
+	if (mode_arg) {
+		if (strcmp(mode_arg, "stepped") && strcmp(mode_arg, "free") &&
+		    strcmp(mode_arg, "madvise"))
+			usage();
+		one_mode[0] = mode_arg;
+		modes = one_mode;
+		nr_modes = 1;
+	}
+
+	ksft_print_header();
+	if (!thp_available())
+		ksft_exit_skip("Transparent Hugepages not available\n");
+
+	page_size = getpagesize();
+	hpage_pmd_size = read_pmd_pagesize();
+	if (!hpage_pmd_size)
+		ksft_exit_fail_msg("Reading PMD pagesize failed\n");
+
+	gup_fd = open("/sys/kernel/debug/gup_test", O_RDWR);
+	if (gup_fd < 0)
+		ksft_exit_skip("/sys/kernel/debug/gup_test requires CONFIG_GUP_TEST and root\n");
+
+	nr_shared_areas = nr_areas_arg > 0 ? nr_areas_arg : DEFAULT_SHARED_AREAS;
+	nr_areas = nr_shared_areas + 1;
+
+	/*
+	 * MREMAP_FIXED unmaps whatever is in the way without saying so, so
+	 * claim the mremap thread's scratch address up front.
+	 */
+	mremap_scratch = (char *)BASE_ADDR + 2 * nr_areas * hpage_pmd_size;
+	if (mmap(mremap_scratch, hpage_pmd_size, PROT_NONE,
+		 MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE,
+		 -1, 0) != (void *)mremap_scratch)
+		ksft_exit_fail_perror("mmap() mremap scratch");
+
+	ksft_set_plan(nr_modes);
+
+	thp_save_settings();
+	thp_read_settings(&settings);
+
+	/* Base of the settings stack; the bottom entry is never popped */
+	thp_push_settings(&settings);
+
+	for (int m = 0; m < nr_modes; m++) {
+		const char *mode = modes[m];
+
+		thp_read_settings(&settings);
+		settings.thp_enabled = THP_MADVISE;
+		settings.thp_defrag = THP_DEFRAG_ALWAYS;
+		settings.shmem_enabled = SHMEM_NEVER;
+		settings.khugepaged.defrag = 1;
+		settings.khugepaged.scan_sleep_millisecs =
+			strcmp(mode, "free") ? 1000 : 0;
+		settings.khugepaged.alloc_sleep_millisecs = 10;
+		/*
+		 * mTHP collapse honours only 0 or HPAGE_PMD_NR - 1 here, and 0
+		 * keeps a step from being spent on PMD allocations that racing
+		 * MADV_DONTNEED will not let succeed.
+		 */
+		settings.khugepaged.max_ptes_none = 0;
+		/* One wake, one pass: the playground plus the forked children's copies */
+		settings.khugepaged.pages_to_scan =
+			nr_areas * (hpage_pmd_size / page_size) * 8;
+		for (i = 0; i < NR_ORDERS; i++) {
+			if (thp_supported_orders() & (1UL << i))
+				settings.hugepages[i].enabled = THP_INHERIT;
+		}
+		thp_push_settings(&settings);
+
+		region = mmap(BASE_ADDR, nr_areas * hpage_pmd_size,
+			      PROT_READ | PROT_WRITE, MAP_ANONYMOUS |
+			      MAP_PRIVATE | MAP_FIXED_NOREPLACE, -1, 0);
+		if (region != BASE_ADDR)
+			ksft_exit_fail_perror("mmap() playground");
+		mremap_area = region + nr_shared_areas * hpage_pmd_size;
+
+		/* Populate so the first pass has something to collapse */
+		for (i = 0; i < nr_shared_areas * hpage_pmd_size / page_size; i++)
+			*(unsigned int *)(region + i * page_size) = pattern(i);
+		memset(mremap_area, 1, hpage_pmd_size);
+		if (madvise(region, nr_areas * hpage_pmd_size, MADV_HUGEPAGE))
+			ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
+
+		for (i = 0; i < nr_threads; i++) {
+			if (!(thread_mask & (1UL << i))) {
+				threads[i] = 0;
+				continue;
+			}
+			if (pthread_create(&threads[i], NULL, thread_fns[i],
+					   (void *)(i + 1)))
+				ksft_exit_fail_perror(thread_names[i]);
+		}
+
+		end_ms = now_ms() + duration_s * 1000UL;
+		if (!strcmp(mode, "stepped")) {
+			while (now_ms() < end_ms && !corrupted) {
+				if (!khugepaged_full_pass(PASS_TIMEOUT_S))
+					ksft_exit_fail_msg("khugepaged pass timed out\n");
+				steps++;
+			}
+		} else if (!strcmp(mode, "free")) {
+			while (now_ms() < end_ms && !corrupted)
+				usleep(100 * 1000);
+		} else {	/* madvise */
+			while (now_ms() < end_ms && !corrupted) {
+				for (i = 0; i < nr_shared_areas; i++) {
+					madvise(region + i * hpage_pmd_size,
+						hpage_pmd_size, MADV_COLLAPSE);
+				}
+				madvise(region, nr_shared_areas * hpage_pmd_size,
+					MADV_DONTNEED);
+				steps++;
+			}
+		}
+
+		stop = 1;
+		for (i = 0; i < nr_threads; i++) {
+			if (threads[i])
+				pthread_join(threads[i], NULL);
+		}
+
+		for (i = 0; i < nr_shared_areas * hpage_pmd_size / page_size; i++)
+			check_page(i);
+
+		ksft_test_result(!corrupted,
+				 "%s: %ds, %d steps, no corruption\n",
+				 mode, duration_s, steps);
+
+		/* The next mode maps the same fixed address with its own settings */
+		munmap(region, nr_areas * hpage_pmd_size);
+		thp_pop_settings();
+		stop = 0;
+		steps = 0;
+
+		if (corrupted) {
+			/* Memory is suspect; the rest would prove nothing */
+			while (++m < nr_modes)
+				ksft_test_result_skip("%s: skipped after corruption\n",
+						      modes[m]);
+			break;
+		}
+	}
+
+	ksft_finished();
+}
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 612a8c4afc53..6990485b1a9d 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -386,6 +386,8 @@ CATEGORY="thp" run_test ./folio_order_check
 
 CATEGORY="thp" run_test ./khugepaged_sync_check
 
+CATEGORY="thp" run_test ./khugepaged_race
+
 CATEGORY="thp" run_test ./khugepaged
 
 CATEGORY="thp" run_test ./khugepaged -s 2
-- 
2.54.0

[PATCH v6 17/19] selftests/mm: race the collapse of windows with holes

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The harness pins max_ptes_none to 0, so khugepaged only collapses a window
once every PTE in it is present.  A window with holes takes a different
route, and never gets raced.  A hole is zero-filled in the new folio
rather than copied.  Which slots count as holes keeps moving under the
racing MADV_DONTNEED, right up to the moment the PMD is detached.

Run both ends of the occupancy scale for every driver mode, one after the
other.  mTHP collapse supports only those two, 0 and HPAGE_PMD_NR - 1, and
coerces anything between them to 0.  Each result says which end it ran:

  ok 1 stepped/strict: 5s, 231 steps, no corruption
  ok 2 stepped/holes: 5s, 194 steps, no corruption

Assisted-by: LLM
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged_race.c | 32 ++++++++++++--------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c
index 66c9e2c10f66..6575045c0482 100644
--- a/tools/testing/selftests/mm/khugepaged_race.c
+++ b/tools/testing/selftests/mm/khugepaged_race.c
@@ -236,6 +236,8 @@ int main(int argc, char **argv)
 	const int nr_threads = ARRAY_SIZE(thread_names);
 	pthread_t threads[ARRAY_SIZE(thread_names)];
 	static const char * const all_modes[] = { "stepped", "free", "madvise" };
+	static const bool occupancies[] = { false, true };	/* strict, holes */
+	const int nr_occupancies = ARRAY_SIZE(occupancies);
 	const char *one_mode[1];
 	const char * const *modes = all_modes;
 	int nr_modes = ARRAY_SIZE(all_modes);
@@ -303,7 +305,7 @@ int main(int argc, char **argv)
 		 -1, 0) != (void *)mremap_scratch)
 		ksft_exit_fail_perror("mmap() mremap scratch");
 
-	ksft_set_plan(nr_modes);
+	ksft_set_plan(nr_modes * nr_occupancies);
 
 	thp_save_settings();
 	thp_read_settings(&settings);
@@ -311,8 +313,9 @@ int main(int argc, char **argv)
 	/* Base of the settings stack; the bottom entry is never popped */
 	thp_push_settings(&settings);
 
-	for (int m = 0; m < nr_modes; m++) {
-		const char *mode = modes[m];
+	for (int run = 0; run < nr_modes * nr_occupancies; run++) {
+		const char *mode = modes[run / nr_occupancies];
+		bool holes = occupancies[run % nr_occupancies];
 
 		thp_read_settings(&settings);
 		settings.thp_enabled = THP_MADVISE;
@@ -322,12 +325,14 @@ int main(int argc, char **argv)
 		settings.khugepaged.scan_sleep_millisecs =
 			strcmp(mode, "free") ? 1000 : 0;
 		settings.khugepaged.alloc_sleep_millisecs = 10;
+
 		/*
-		 * mTHP collapse honours only 0 or HPAGE_PMD_NR - 1 here, and 0
-		 * keeps a step from being spent on PMD allocations that racing
-		 * MADV_DONTNEED will not let succeed.
+		 * mTHP collapse honours only 0 or HPAGE_PMD_NR - 1 here.  The two
+		 * ends race different paths: a strict window has every PTE
+		 * present, a hole-heavy one is mostly zero-filled.
 		 */
-		settings.khugepaged.max_ptes_none = 0;
+		settings.khugepaged.max_ptes_none = holes ?
+			(hpage_pmd_size / page_size) - 1 : 0;
 		/* One wake, one pass: the playground plus the forked children's copies */
 		settings.khugepaged.pages_to_scan =
 			nr_areas * (hpage_pmd_size / page_size) * 8;
@@ -393,8 +398,9 @@ int main(int argc, char **argv)
 			check_page(i);
 
 		ksft_test_result(!corrupted,
-				 "%s: %ds, %d steps, no corruption\n",
-				 mode, duration_s, steps);
+				 "%s/%s: %ds, %d steps, no corruption\n",
+				 mode, holes ? "holes" : "strict",
+				 duration_s, steps);
 
 		/* The next mode maps the same fixed address with its own settings */
 		munmap(region, nr_areas * hpage_pmd_size);
@@ -404,9 +410,11 @@ int main(int argc, char **argv)
 
 		if (corrupted) {
 			/* Memory is suspect; the rest would prove nothing */
-			while (++m < nr_modes)
-				ksft_test_result_skip("%s: skipped after corruption\n",
-						      modes[m]);
+			while (++run < nr_modes * nr_occupancies)
+				ksft_test_result_skip("%s/%s: skipped after corruption\n",
+						      modes[run / nr_occupancies],
+						      occupancies[run % nr_occupancies] ?
+						      "holes" : "strict");
 			break;
 		}
 	}
-- 
2.54.0

[PATCH v6 18/19] selftests/mm: add memory-pressure threads to the khugepaged race harness

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The harness races collapse against faults, pins, fork, mremap and
MADV_DONTNEED, but nothing in it runs reclaim or compaction against the
collapse.

Add two more threads, and run every mode and occupancy limit both with and
without them:

 - pageout: cycles MADV_PAGEOUT over a region of its own, faults it back
   in and checks the content each round, since a page's pattern must
   survive the trip through swap.  Left out when the host has no swap,
   because then there is no anon reclaim to drive.

 - compactor: writes /proc/sys/vm/compact_memory in a loop.  Compaction
   isolates and migrates folios, so it competes with a collapse for the
   pages it is gathering, with refcount elevations and migration entries
   of its own.

Each result says whether it ran under pressure:

  ok 2 stepped/strict/pressure: 5s, 88 steps, no corruption

A full run is now twelve combinations; -m picks one mode, -d shortens
each run.

Assisted-by: LLM
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged_race.c | 142 ++++++++++++++++---
 1 file changed, 122 insertions(+), 20 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c
index 6575045c0482..68046f0bf6d3 100644
--- a/tools/testing/selftests/mm/khugepaged_race.c
+++ b/tools/testing/selftests/mm/khugepaged_race.c
@@ -44,6 +44,8 @@ static unsigned long page_size;
 static char *region;
 static char *mremap_area;
 static char *mremap_scratch;
+static char *pageout_area;
+static size_t pageout_size;
 static int gup_fd = -1;
 static volatile int stop;
 static volatile int corrupted;
@@ -204,6 +206,69 @@ static void *mremapper_fn(void *arg)
 	return NULL;
 }
 
+/*
+ * Swap traffic and LRU churn on a region nothing else writes, so a page's
+ * pattern must survive the trip through swap exactly.
+ */
+static void *pageout_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+	unsigned long nr = pageout_size / page_size;
+	unsigned long i;
+
+	for (i = 0; i < nr; i++)
+		*(unsigned int *)(pageout_area + i * page_size) = pattern(i);
+
+	while (!stop) {
+		madvise(pageout_area, pageout_size, MADV_PAGEOUT);
+		for (i = 0; i < nr && !stop; i++) {
+			unsigned int val = *(unsigned int *)(pageout_area +
+							     i * page_size);
+
+			if (val != pattern(i)) {
+				corrupted = 1;
+				ksft_print_msg("Pageout corruption at page %lu: %#x != %#x\n",
+					       i, val, pattern(i));
+			}
+		}
+		usleep(rand_r(&seed) % 2000);
+	}
+	return NULL;
+}
+
+/* Compaction migrates the collapse sources while they are being gathered */
+static void *compactor_fn(void *arg)
+{
+	unsigned int seed = (unsigned long)arg;
+	int fd = open("/proc/sys/vm/compact_memory", O_WRONLY);
+
+	if (fd < 0) {
+		ksft_print_msg("No compact_memory; compactor idle\n");
+		return NULL;
+	}
+	while (!stop) {
+		if (write(fd, "1", 1) < 0)
+			break;
+		usleep(10000 + rand_r(&seed) % 100000);
+	}
+	close(fd);
+	return NULL;
+}
+
+static bool swap_available(void)
+{
+	char line[256];
+	int lines = 0;
+	FILE *fp = fopen("/proc/swaps", "r");
+
+	if (!fp)
+		return false;
+	while (fgets(line, sizeof(line), fp))
+		lines++;
+	fclose(fp);
+	return lines > 1;
+}
+
 static unsigned long now_ms(void)
 {
 	struct timeval tv;
@@ -227,17 +292,23 @@ int main(int argc, char **argv)
 {
 	static const char * const thread_names[] = {
 		"faulter", "faulter2", "dontneed", "pinner", "forker",
-		"mremapper",
+		"mremapper", "pageout", "compactor",
 	};
 	void *(*const thread_fns[])(void *) = {
 		faulter_fn, faulter_fn, dontneed_fn, pinner_fn, forker_fn,
-		mremapper_fn,
+		mremapper_fn, pageout_fn, compactor_fn,
 	};
+	enum { T_FAULTER, T_FAULTER2, T_DONTNEED, T_PINNER, T_FORKER,
+	       T_MREMAPPER, T_PAGEOUT, T_COMPACTOR };
+	const unsigned long pageout_bit = 1UL << T_PAGEOUT;
+	const unsigned long compactor_bit = 1UL << T_COMPACTOR;
 	const int nr_threads = ARRAY_SIZE(thread_names);
 	pthread_t threads[ARRAY_SIZE(thread_names)];
 	static const char * const all_modes[] = { "stepped", "free", "madvise" };
 	static const bool occupancies[] = { false, true };	/* strict, holes */
+	static const bool pressures[] = { false, true };	/* quiet, under pressure */
 	const int nr_occupancies = ARRAY_SIZE(occupancies);
+	const int nr_pressures = ARRAY_SIZE(pressures);
 	const char *one_mode[1];
 	const char * const *modes = all_modes;
 	int nr_modes = ARRAY_SIZE(all_modes);
@@ -246,6 +317,9 @@ int main(int argc, char **argv)
 	unsigned long end_ms;
 	int duration_s = 5;
 	unsigned long thread_mask = ~0UL;
+	unsigned long base_mask;
+	bool have_swap;
+	char label[64];
 	int nr_areas_arg = 0;
 	unsigned long i;
 	int steps = 0;
@@ -305,7 +379,13 @@ int main(int argc, char **argv)
 		 -1, 0) != (void *)mremap_scratch)
 		ksft_exit_fail_perror("mmap() mremap scratch");
 
-	ksft_set_plan(nr_modes * nr_occupancies);
+	base_mask = thread_mask;
+	have_swap = swap_available();
+	if (!have_swap)
+		/* No swap, no anon reclaim: compaction-only pressure */
+		ksft_print_msg("no swap: the pageout thread is not started\n");
+
+	ksft_set_plan(nr_modes * nr_occupancies * nr_pressures);
 
 	thp_save_settings();
 	thp_read_settings(&settings);
@@ -313,9 +393,25 @@ int main(int argc, char **argv)
 	/* Base of the settings stack; the bottom entry is never popped */
 	thp_push_settings(&settings);
 
-	for (int run = 0; run < nr_modes * nr_occupancies; run++) {
-		const char *mode = modes[run / nr_occupancies];
-		bool holes = occupancies[run % nr_occupancies];
+	for (int run = 0; run < nr_modes * nr_occupancies * nr_pressures; run++) {
+		int rem = run % (nr_occupancies * nr_pressures);
+		const char *mode = modes[run / (nr_occupancies * nr_pressures)];
+		bool holes = occupancies[rem / nr_pressures];
+		bool pressure = pressures[rem % nr_pressures];
+
+		snprintf(label, sizeof(label), "%s/%s%s", mode,
+			 holes ? "holes" : "strict", pressure ? "/pressure" : "");
+		if (corrupted) {
+			/* Memory is suspect; the rest would prove nothing */
+			ksft_test_result_skip("%s: skipped after corruption\n", label);
+			continue;
+		}
+
+		thread_mask = base_mask;
+		if (!pressure)
+			thread_mask &= ~(pageout_bit | compactor_bit);
+		else if (!have_swap)
+			thread_mask &= ~pageout_bit;
 
 		thp_read_settings(&settings);
 		settings.thp_enabled = THP_MADVISE;
@@ -349,6 +445,20 @@ int main(int argc, char **argv)
 			ksft_exit_fail_perror("mmap() playground");
 		mremap_area = region + nr_shared_areas * hpage_pmd_size;
 
+		if (thread_mask & pageout_bit) {
+			/* Enough to drive real reclaim without swamping a small guest */
+			pageout_size = 4 * hpage_pmd_size;
+			if (pageout_size < 16UL << 20)
+				pageout_size = 16UL << 20;
+			if (pageout_size > 64UL << 20)
+				pageout_size = 64UL << 20;
+			pageout_area = mmap(NULL, pageout_size,
+					    PROT_READ | PROT_WRITE,
+					    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+			if (pageout_area == MAP_FAILED)
+				ksft_exit_fail_perror("mmap() pageout area");
+		}
+
 		/* Populate so the first pass has something to collapse */
 		for (i = 0; i < nr_shared_areas * hpage_pmd_size / page_size; i++)
 			*(unsigned int *)(region + i * page_size) = pattern(i);
@@ -397,26 +507,18 @@ int main(int argc, char **argv)
 		for (i = 0; i < nr_shared_areas * hpage_pmd_size / page_size; i++)
 			check_page(i);
 
-		ksft_test_result(!corrupted,
-				 "%s/%s: %ds, %d steps, no corruption\n",
-				 mode, holes ? "holes" : "strict",
-				 duration_s, steps);
+		ksft_test_result(!corrupted, "%s: %ds, %d steps, no corruption\n",
+				 label, duration_s, steps);
 
 		/* The next mode maps the same fixed address with its own settings */
 		munmap(region, nr_areas * hpage_pmd_size);
+		if (pageout_area) {
+			munmap(pageout_area, pageout_size);
+			pageout_area = NULL;
+		}
 		thp_pop_settings();
 		stop = 0;
 		steps = 0;
-
-		if (corrupted) {
-			/* Memory is suspect; the rest would prove nothing */
-			while (++run < nr_modes * nr_occupancies)
-				ksft_test_result_skip("%s/%s: skipped after corruption\n",
-						      modes[run / nr_occupancies],
-						      occupancies[run % nr_occupancies] ?
-						      "holes" : "strict");
-			break;
-		}
 	}
 
 	ksft_finished();
-- 
2.54.0

[PATCH v6 19/19] selftests/mm: zap whole PTE tables in the khugepaged race harness

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The harness's MADV_DONTNEED thread zaps 1 to 32 pages at a time, never a
whole PMD-aligned area, and only a zap that covers a full table frees the
table itself (CONFIG_PT_RECLAIM).

Make the thread zap a whole PMD-aligned area about one iteration in 64,
and keep the fine-grained zaps as the common case.  The new case frees
page tables, racing that against a collapse walking the same table.

Assisted-by: LLM
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 tools/testing/selftests/mm/khugepaged_race.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c
index 68046f0bf6d3..abb0678522cd 100644
--- a/tools/testing/selftests/mm/khugepaged_race.c
+++ b/tools/testing/selftests/mm/khugepaged_race.c
@@ -118,8 +118,21 @@ static void *dontneed_fn(void *arg)
 		unsigned long page_idx = rand_page(&seed);
 		unsigned long nr = 1UL << (rand_r(&seed) % 6);	/* 1..32 pages */
 
-		madvise(region + page_idx * page_size,
-			room_from(page_idx, nr) * page_size, MADV_DONTNEED);
+		/*
+		 * Now and then zap a whole PMD-aligned area: only a zap that
+		 * covers the full table frees the table itself (CONFIG_PT_RECLAIM).
+		 */
+		if (!(rand_r(&seed) % 64)) {
+			unsigned long area = page_idx /
+					(hpage_pmd_size / page_size);
+
+			madvise(region + area * hpage_pmd_size,
+				hpage_pmd_size, MADV_DONTNEED);
+		} else {
+			madvise(region + page_idx * page_size,
+				room_from(page_idx, nr) * page_size,
+				MADV_DONTNEED);
+		}
 		usleep(rand_r(&seed) % 500);
 	}
 	return NULL;
-- 
2.54.0

Re: [PATCH v6 00/19] selftests/mm: improve khugepaged coverage

[Andrew Morton]

On Sat, 19 Sep 2026 01:24:30 +0100 Kiryl Shutsemau <kirill@shutemov.name> wrote:

> From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
> 
> khugepaged collapses to mTHP orders since 7.2, and 7.3 added three
> selftest cases for it: the generic collapse cases run at one order named
> by -c, with the result detected by counting folios of that order.
> 
> That leaves the collapse path largely untested.  The suite does not run
> where a PMD is 512M.  A folio count cannot say where a collapse landed.
> Fixed sleeps cannot tell "not collapsed" from "not scanned yet".  And
> nothing exercises collapse under contention.
> 
> Close those gaps in order:
> 

Thanks, I've added this to mm-new.

I'd previous added v5 but it never really got testing exposure due to a
messy interaction with other changes which I didn't get onto fixing.