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[2003:d8:2f47:2b00:c5f3:4053:2918:d17c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4587ac58162sm101784195e9.18.2025.07.28.08.06.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 28 Jul 2025 08:06:40 -0700 (PDT) Message-ID: Date: Mon, 28 Jul 2025 17:06:38 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/5] selftests: prctl: introduce tests for disabling THPs completely To: Usama Arif , Andrew Morton , linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org, corbet@lwn.net, rppt@kernel.org, surenb@google.com, mhocko@suse.com, hannes@cmpxchg.org, baohua@kernel.org, shakeel.butt@linux.dev, riel@surriel.com, ziy@nvidia.com, laoar.shao@gmail.com, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, vbabka@suse.cz, jannh@google.com, Arnd Bergmann , sj@kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com References: <20250725162258.1043176-1-usamaarif642@gmail.com> <20250725162258.1043176-5-usamaarif642@gmail.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 25.07.25 18:22, Usama Arif wrote: > The test will set the global system THP setting to madvise and > the 2M setting to inherit before it starts (and reset to original > at teardown) > > This tests if the process can: > - successfully set and get the policy to disable THPs completely. > - never get a hugepage when the THPs are completely disabled, > including with MADV_HUGE and MADV_COLLAPSE. > - successfully reset the policy of the process. > - get hugepages only on MADV_HUGE and MADV_COLLAPSE after reset. > - repeat the above tests in a forked process to make sure > the policy is carried across forks. > > Signed-off-by: Usama Arif > --- > tools/testing/selftests/mm/.gitignore | 1 + > tools/testing/selftests/mm/Makefile | 1 + > .../testing/selftests/mm/prctl_thp_disable.c | 162 ++++++++++++++++++ > 3 files changed, 164 insertions(+) > create mode 100644 tools/testing/selftests/mm/prctl_thp_disable.c > > diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore > index e7b23a8a05fe..eb023ea857b3 100644 > --- a/tools/testing/selftests/mm/.gitignore > +++ b/tools/testing/selftests/mm/.gitignore > @@ -58,3 +58,4 @@ pkey_sighandler_tests_32 > pkey_sighandler_tests_64 > guard-regions > merge > +prctl_thp_disable > diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile > index d13b3cef2a2b..2bb8d3ebc17c 100644 > --- a/tools/testing/selftests/mm/Makefile > +++ b/tools/testing/selftests/mm/Makefile > @@ -86,6 +86,7 @@ TEST_GEN_FILES += on-fault-limit > TEST_GEN_FILES += pagemap_ioctl > TEST_GEN_FILES += pfnmap > TEST_GEN_FILES += process_madv > +TEST_GEN_FILES += prctl_thp_disable > TEST_GEN_FILES += thuge-gen > TEST_GEN_FILES += transhuge-stress > TEST_GEN_FILES += uffd-stress > diff --git a/tools/testing/selftests/mm/prctl_thp_disable.c b/tools/testing/selftests/mm/prctl_thp_disable.c > new file mode 100644 > index 000000000000..52f7e6659b1f > --- /dev/null > +++ b/tools/testing/selftests/mm/prctl_thp_disable.c > @@ -0,0 +1,162 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Basic tests for PR_GET/SET_THP_DISABLE prctl calls > + * > + * Author(s): Usama Arif > + */ > +#include > +#include > +#include > +#include > +#include > +#include > +#include > + > +#include "../kselftest_harness.h" > +#include "thp_settings.h" > +#include "vm_util.h" > + > +#ifndef PR_THP_DISABLE_EXCEPT_ADVISED > +#define PR_THP_DISABLE_EXCEPT_ADVISED (1 << 1) > +#endif Into patch #2 I guess. > + > +#define NR_HUGEPAGES 6 > + > +static int sz2ord(size_t size, size_t pagesize) > +{ > + return __builtin_ctzll(size / pagesize); > +} > + > +enum madvise_buffer { > + NONE, > + HUGE, > + COLLAPSE > +}; Is that rather something like: enum thp_collapse_type { THP_COLLAPSE_NONE, THP_COLLAPSE_MADV_HUGEPAGE, /* MADV_HUGEPAGE before access */ THP_COLLAPSE_MADV_COLLAPSE, /* MADV_COLLAPSE after access */ }; > + > +/* > + * Function to mmap a buffer, fault it in, madvise it appropriately (before > + * page fault for MADV_HUGE, and after for MADV_COLLAPSE), and check if the > + * mmap region is huge. > + * returns: > + * 0 if test doesn't give hugepage > + * 1 if test gives a hugepage > + * -1 if mmap fails > + */ > +static int test_mmap_thp(enum madvise_buffer madvise_buf, size_t pmdsize) > +{ > + int ret; > + int buf_size = NR_HUGEPAGES * pmdsize; > + > + char *buffer = (char *)mmap(NULL, buf_size, PROT_READ | PROT_WRITE, > + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); Can we get rid of NR_HUGEPAGES and just use a single one, aligning in a bigger area? This is similar to what we do in cow.c /* For alignment purposes, we need twice the thp size. */ mmap_size = 2 * pmdsize; mmap_area = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (mmap_area == MAP_FAILED) return -errno; /* todo, document that above */ buffer = (char *)(((uintptr_t)mmap_area + pmdsize) & ~(pmdsize - 1)); ... ret = check_huge_anon(buffer, NR_HUGEPAGES, pmdsize); ... munmap(mmap_area, mmap_size); > + if (buffer == MAP_FAILED) > + return -1; > + > + if (madvise_buf == HUGE) > + madvise(buffer, buf_size, MADV_HUGEPAGE); > + > + /* Ensure memory is allocated */ > + memset(buffer, 1, buf_size); > + > + if (madvise_buf == COLLAPSE) > + madvise(buffer, buf_size, MADV_COLLAPSE); > + > + ret = check_huge_anon(buffer, NR_HUGEPAGES, pmdsize); > + munmap(buffer, buf_size); > + return ret; > +} Empty line missing :) > +FIXTURE(prctl_thp_disable_completely) > +{ > + struct thp_settings settings; > + size_t pmdsize; > +}; > + > +FIXTURE_SETUP(prctl_thp_disable_completely) > +{ > + if (!thp_is_enabled()) > + SKIP(return, "Transparent Hugepages not available\n"); Heh, not completely correct. enabled != available. Do we want a thp_available() that is essentially the first part of thp_is_enabled() ? > + > + self->pmdsize = read_pmd_pagesize(); > + if (!self->pmdsize) > + SKIP(return, "Unable to read PMD size\n"); > + > + thp_read_settings(&self->settings); > + self->settings.thp_enabled = THP_MADVISE; > + self->settings.hugepages[sz2ord(self->pmdsize, getpagesize())].enabled = THP_INHERIT; > + thp_save_settings(); > + thp_push_settings(&self->settings); push without pop, should that be alarming? :) Can we just use thp_write_settings()? (not sure why that push/pop is required ... is it?) > +} > + > +FIXTURE_TEARDOWN(prctl_thp_disable_completely) > +{> + thp_restore_settings(); > +} > + > +/* prctl_thp_disable_except_madvise fixture sets system THP setting to madvise */ > +static void prctl_thp_disable_completely(struct __test_metadata *const _metadata, > + size_t pmdsize) > +{ > + int res = 0; > + > + res = prctl(PR_GET_THP_DISABLE, NULL, NULL, NULL, NULL); > + ASSERT_EQ(res, 1); > + > + /* global = madvise, process = never, we shouldn't get HPs even with madvise */ s/HPs/THPs/ > + res = test_mmap_thp(NONE, pmdsize); > + ASSERT_EQ(res, 0); > + > + res = test_mmap_thp(HUGE, pmdsize); > + ASSERT_EQ(res, 0); > + > + res = test_mmap_thp(COLLAPSE, pmdsize); > + ASSERT_EQ(res, 0); > + > + /* Reset to system policy */ > + res = prctl(PR_SET_THP_DISABLE, 0, NULL, NULL, NULL); > + ASSERT_EQ(res, 0); > + > + /* global = madvise */ > + res = test_mmap_thp(NONE, pmdsize); > + ASSERT_EQ(res, 0); > + > + res = test_mmap_thp(HUGE, pmdsize); > + ASSERT_EQ(res, 1); > + > + res = test_mmap_thp(COLLAPSE, pmdsize); > + ASSERT_EQ(res, 1); Makes me wonder: should we test for global=always and global=always? (or simply for all possible values, including global=never if easily possible?) At least testing with global=always should exercise more possible paths than global=always (esp., test_mmap_thp(NONE, pmdsize) which would never apply in madvise mode). -- Cheers, David / dhildenb