[PATCH v3] mm/memory-failure: Support disabling soft offline for HugeTLB pages

[Kyle Meyer <kyle.meyer@hpe.com>]

Soft offlining a HugeTLB page dissolves it, permanently reducing the
HugeTLB page pool. This can be problematic for workloads that depend on
a fixed number of HugeTLB pages.

Currently, soft offline must be disabled to prevent HugeTLB pages from
being soft offlined.

This patch allows soft offline to be disabled for HugeTLB pages while
remaining enabled for non-HugeTLB pages.

Commit 56374430c5dfc ("mm/memory-failure: userspace controls
soft-offlining pages") introduced the following sysctl interface to
control soft offline:

/proc/sys/vm/enable_soft_offline

The interface does not distinguish between page types:

    0 - Soft offline is disabled
    1 - Soft offline is enabled

Convert enable_soft_offline to a bitmask and support disabling soft
offline for HugeTLB pages:

Bits:

    0 - Enable soft offline
    1 - Disable soft offline for HugeTLB pages

Supported values:

    0 - Soft offline is disabled
    1 - Soft offline is enabled
    3 - Soft offline is enabled (disabled for HugeTLB pages)

Existing behavior is preserved.

Update documentation and HugeTLB soft offline selftests.

Suggested-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
---

Tony's patch:
* https://lore.kernel.org/all/20250904155720.22149-1-tony.luck@intel.com

v1:
* https://lore.kernel.org/all/aMGkAI3zKlVsO0S2@hpe.com

v1 -> v2:
* Make the interface extensible, as suggested by David.
* Preserve existing behavior, as suggested by Jiaqi and David.
* https://lore.kernel.org/all/aMiu_Uku6Y5ZbuhM@hpe.com

v2 -> v3:
* Minor documentation updates.
* Use page_folio(page) instead of pfn_folio(pfn) for HugeTLB page check.

---
 .../ABI/testing/sysfs-memory-page-offline     |  3 +++
 Documentation/admin-guide/sysctl/vm.rst       | 27 +++++++++++++++----
 mm/memory-failure.c                           | 17 +++++++++---
 .../selftests/mm/hugetlb-soft-offline.c       | 19 ++++++++++---
 4 files changed, 54 insertions(+), 12 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-memory-page-offline b/Documentation/ABI/testing/sysfs-memory-page-offline
index 00f4e35f916f..19aa539fb910 100644
--- a/Documentation/ABI/testing/sysfs-memory-page-offline
+++ b/Documentation/ABI/testing/sysfs-memory-page-offline
@@ -20,6 +20,9 @@ Description:
 		number, or a error when the offlining failed.  Reading
 		the file is not allowed.
 
+		Soft-offline can be controlled via sysctl:
+		Documentation/admin-guide/sysctl/vm.rst
+
 What:		/sys/devices/system/memory/hard_offline_page
 Date:		Sep 2009
 KernelVersion:	2.6.33
diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index 5b318d17aa4b..ee1941e44643 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -309,16 +309,33 @@ physical memory) vs performance / capacity implications in transparent and
 HugeTLB cases.
 
 For all architectures, enable_soft_offline controls whether to soft offline
-memory pages.  When set to 1, kernel attempts to soft offline the pages
-whenever it thinks needed.  When set to 0, kernel returns EOPNOTSUPP to
-the request to soft offline the pages.  Its default value is 1.
+memory pages.
 
-It is worth mentioning that after setting enable_soft_offline to 0, the
+enable_soft_offline is a bitmask:
+
+Bits::
+
+	0 - Enable soft offline
+	1 - Disable soft offline for HugeTLB pages
+
+Supported values::
+
+	0 - Soft offline is disabled
+	1 - Soft offline is enabled
+	3 - Soft offline is enabled (disabled for HugeTLB pages)
+
+The default value is 1.
+
+If soft offline is disabled for the requested page type, EOPNOTSUPP is returned.
+
+It is worth mentioning that after disabling soft offline, the
 following requests to soft offline pages will not be performed:
 
+- Request to soft offline pages from sysfs.
+
 - Request to soft offline pages from RAS Correctable Errors Collector.
 
-- On ARM, the request to soft offline pages from GHES driver.
+- Request to soft offline pages from GHES driver.
 
 - On PARISC, the request to soft offline pages from Page Deallocation Table.
 
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index a8b03e2920ba..6c4ce39f46df 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -69,11 +69,14 @@
 #include "page_alloc.h"
 #include "internal.h"
 
+#define SOFT_OFFLINE_ENABLED		BIT(0)
+#define SOFT_OFFLINE_SKIP_HUGETLB	BIT(1)
+
 static int sysctl_memory_failure_early_kill __read_mostly;
 
 static int sysctl_memory_failure_recovery __read_mostly = 1;
 
-static int sysctl_enable_soft_offline __read_mostly = 1;
+static int sysctl_enable_soft_offline __read_mostly = SOFT_OFFLINE_ENABLED;
 
 static int sysctl_panic_on_unrecoverable_mf __read_mostly;
 
@@ -157,7 +160,7 @@ static const struct ctl_table memory_failure_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
+		.extra2		= SYSCTL_THREE,
 	},
 	{
 		.procname	= "panic_on_unrecoverable_memory_failure",
@@ -2982,12 +2985,20 @@ int soft_offline_page(unsigned long pfn, int flags)
 		return -EIO;
 	}
 
-	if (!sysctl_enable_soft_offline) {
+	if (!(sysctl_enable_soft_offline & SOFT_OFFLINE_ENABLED)) {
 		pr_info_once("disabled by /proc/sys/vm/enable_soft_offline\n");
 		put_ref_page(pfn, flags);
 		return -EOPNOTSUPP;
 	}
 
+	if (sysctl_enable_soft_offline & SOFT_OFFLINE_SKIP_HUGETLB) {
+		if (folio_test_hugetlb(page_folio(page))) {
+			pr_info_once("disabled for HugeTLB pages by /proc/sys/vm/enable_soft_offline\n");
+			put_ref_page(pfn, flags);
+			return -EOPNOTSUPP;
+		}
+	}
+
 	mutex_lock(&mf_mutex);
 
 	if (PageHWPoison(page)) {
diff --git a/tools/testing/selftests/mm/hugetlb-soft-offline.c b/tools/testing/selftests/mm/hugetlb-soft-offline.c
index bc202e4ed2bd..9837c315a81e 100644
--- a/tools/testing/selftests/mm/hugetlb-soft-offline.c
+++ b/tools/testing/selftests/mm/hugetlb-soft-offline.c
@@ -5,6 +5,8 @@
  *   offlining failed with EOPNOTSUPP.
  * - if enable_soft_offline = 1, a hugepage should be dissolved and
  *   nr_hugepages/free_hugepages should be reduced by 1.
+ * - if enable_soft_offline = 3, HugeTLB pages should stay intact and soft
+ *   offlining failed with EOPNOTSUPP.
  *
  * The test allocates 8 default hugepages
  */
@@ -31,6 +33,9 @@
 
 #define EPREFIX " !!! "
 
+#define SOFT_OFFLINE_ENABLED		(1 << 0)
+#define SOFT_OFFLINE_SKIP_HUGETLB	(1 << 1)
+
 static int do_soft_offline(int fd, size_t len, int expect_errno)
 {
 	char *filemap = NULL;
@@ -55,6 +60,7 @@ static int do_soft_offline(int fd, size_t len, int expect_errno)
 	ksft_print_msg("Allocated %#lx bytes of hugetlb pages\n", len);
 
 	hwp_addr = filemap + len / 2;
+	errno = 0;
 	ret = madvise(hwp_addr, pagesize, MADV_SOFT_OFFLINE);
 	ksft_print_msg("MADV_SOFT_OFFLINE %p ret=%d, errno=%d\n",
 		       hwp_addr, ret, errno);
@@ -82,7 +88,7 @@ static int set_enable_soft_offline(int value)
 	char cmd[256] = {0};
 	FILE *cmdfile = NULL;
 
-	if (value != 0 && value != 1)
+	if (value < 0 || value > 3)
 		return -EINVAL;
 
 	sprintf(cmd, "echo %d > /proc/sys/vm/enable_soft_offline", value);
@@ -128,13 +134,17 @@ static int create_hugetlbfs_file(struct statfs *file_stat)
 static void test_soft_offline_common(int enable_soft_offline)
 {
 	int fd;
-	int expect_errno = enable_soft_offline ? 0 : EOPNOTSUPP;
+	int expect_errno = 0;
 	struct statfs file_stat;
 	unsigned long hugepagesize_kb = 0;
 	unsigned long nr_hugepages_before = 0;
 	unsigned long nr_hugepages_after = 0;
 	int ret;
 
+	if (!(enable_soft_offline & SOFT_OFFLINE_ENABLED) ||
+	    (enable_soft_offline & SOFT_OFFLINE_SKIP_HUGETLB))
+		expect_errno = EOPNOTSUPP;
+
 	ksft_print_msg("Test soft-offline when enabled_soft_offline=%d\n",
 		       enable_soft_offline);
 
@@ -165,7 +175,7 @@ static void test_soft_offline_common(int enable_soft_offline)
 	// No need for the hugetlbfs file from now on.
 	close(fd);
 
-	if (enable_soft_offline) {
+	if (expect_errno == 0) {
 		if (nr_hugepages_before != nr_hugepages_after + 1) {
 			ksft_test_result_fail("MADV_SOFT_OFFLINE should reduced 1 hugepage\n");
 			return;
@@ -190,8 +200,9 @@ int main(int argc, char **argv)
 	if (!hugetlb_setup_default(8))
 		ksft_exit_skip("not enough hugetlb pages\n");
 
-	ksft_set_plan(2);
+	ksft_set_plan(3);
 
+	test_soft_offline_common(3);
 	test_soft_offline_common(1);
 	test_soft_offline_common(0);
 
-- 
2.51.0