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Wed, 13 Aug 2025 06:57:34 -0700 (PDT) From: Usama Arif To: Andrew Morton , david@redhat.com, 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, Usama Arif Subject: [PATCH v4 6/7] selftests: prctl: introduce tests for disabling THPs completely Date: Wed, 13 Aug 2025 14:55:41 +0100 Message-ID: <20250813135642.1986480-7-usamaarif642@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20250813135642.1986480-1-usamaarif642@gmail.com> References: <20250813135642.1986480-1-usamaarif642@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The test will set the global system THP setting to never, madvise or always depending on the fixture variant and the 2M setting to inherit before it starts (and reset to original at teardown). The fixture setup will also test if PR_SET_THP_DISABLE prctl call can be made to disable all THPs and skip if it fails. This tests if the process can: - successfully get the policy to disable THPs completely. - never get a hugepage when the THPs are completely disabled with the prctl, including with MADV_HUGE and MADV_COLLAPSE. - successfully reset the policy of the process. - after reset, only get hugepages with: - MADV_COLLAPSE when policy is set to never. - MADV_HUGE and MADV_COLLAPSE when policy is set to madvise. - always when policy is set to "always". - repeat the above tests in a forked process to make sure the policy is carried across forks. Signed-off-by: Usama Arif Acked-by: David Hildenbrand --- tools/testing/selftests/mm/.gitignore | 1 + tools/testing/selftests/mm/Makefile | 1 + .../testing/selftests/mm/prctl_thp_disable.c | 168 ++++++++++++++++++ tools/testing/selftests/mm/thp_settings.c | 9 +- tools/testing/selftests/mm/thp_settings.h | 1 + 5 files changed, 179 insertions(+), 1 deletion(-) 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 e7b23a8a05fe2..eb023ea857b31 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 d75f1effcb791..bd5d17beafa64 100644 --- a/tools/testing/selftests/mm/Makefile +++ b/tools/testing/selftests/mm/Makefile @@ -87,6 +87,7 @@ 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 0000000000000..8845e9f414560 --- /dev/null +++ b/tools/testing/selftests/mm/prctl_thp_disable.c @@ -0,0 +1,168 @@ +// 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" + +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 + * -errno if mmap fails + */ +static int test_mmap_thp(enum thp_collapse_type madvise_buf, size_t pmdsize) +{ + char *mem, *mmap_mem; + size_t mmap_size; + int ret; + + /* For alignment purposes, we need twice the THP size. */ + mmap_size = 2 * pmdsize; + mmap_mem = (char *)mmap(NULL, mmap_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (mmap_mem == MAP_FAILED) + return -errno; + + /* We need a THP-aligned memory area. */ + mem = (char *)(((uintptr_t)mmap_mem + pmdsize) & ~(pmdsize - 1)); + + if (madvise_buf == THP_COLLAPSE_MADV_HUGEPAGE) + madvise(mem, pmdsize, MADV_HUGEPAGE); + + /* Ensure memory is allocated */ + memset(mem, 1, pmdsize); + + if (madvise_buf == THP_COLLAPSE_MADV_COLLAPSE) + madvise(mem, pmdsize, MADV_COLLAPSE); + + /* HACK: make sure we have a separate VMA that we can check reliably. */ + mprotect(mem, pmdsize, PROT_READ); + + ret = check_huge_anon(mem, 1, pmdsize); + munmap(mmap_mem, mmap_size); + return ret; +} + +static void prctl_thp_disable_completely_test(struct __test_metadata *const _metadata, + size_t pmdsize, + enum thp_enabled thp_policy) +{ + ASSERT_EQ(prctl(PR_GET_THP_DISABLE, NULL, NULL, NULL, NULL), 1); + + /* tests after prctl overrides global policy */ + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_NONE, pmdsize), 0); + + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_HUGEPAGE, pmdsize), 0); + + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_COLLAPSE, pmdsize), 0); + + /* Reset to global policy */ + ASSERT_EQ(prctl(PR_SET_THP_DISABLE, 0, NULL, NULL, NULL), 0); + + /* tests after prctl is cleared, and only global policy is effective */ + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_NONE, pmdsize), + thp_policy == THP_ALWAYS ? 1 : 0); + + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_HUGEPAGE, pmdsize), + thp_policy == THP_NEVER ? 0 : 1); + + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_COLLAPSE, pmdsize), 1); +} + +FIXTURE(prctl_thp_disable_completely) +{ + struct thp_settings settings; + size_t pmdsize; +}; + +FIXTURE_VARIANT(prctl_thp_disable_completely) +{ + enum thp_enabled thp_policy; +}; + +FIXTURE_VARIANT_ADD(prctl_thp_disable_completely, never) +{ + .thp_policy = THP_NEVER, +}; + +FIXTURE_VARIANT_ADD(prctl_thp_disable_completely, madvise) +{ + .thp_policy = THP_MADVISE, +}; + +FIXTURE_VARIANT_ADD(prctl_thp_disable_completely, always) +{ + .thp_policy = THP_ALWAYS, +}; + +FIXTURE_SETUP(prctl_thp_disable_completely) +{ + if (!thp_available()) + SKIP(return, "Transparent Hugepages not available\n"); + + self->pmdsize = read_pmd_pagesize(); + if (!self->pmdsize) + SKIP(return, "Unable to read PMD size\n"); + + if (prctl(PR_SET_THP_DISABLE, 1, NULL, NULL, NULL)) + SKIP(return, "Unable to disable THPs completely for the process\n"); + + thp_save_settings(); + thp_read_settings(&self->settings); + self->settings.thp_enabled = variant->thp_policy; + self->settings.hugepages[sz2ord(self->pmdsize, getpagesize())].enabled = THP_INHERIT; + thp_write_settings(&self->settings); +} + +FIXTURE_TEARDOWN(prctl_thp_disable_completely) +{ + thp_restore_settings(); +} + +TEST_F(prctl_thp_disable_completely, nofork) +{ + prctl_thp_disable_completely_test(_metadata, self->pmdsize, variant->thp_policy); +} + +TEST_F(prctl_thp_disable_completely, fork) +{ + int ret = 0; + pid_t pid; + + /* Make sure prctl changes are carried across fork */ + pid = fork(); + ASSERT_GE(pid, 0); + + if (!pid) + prctl_thp_disable_completely_test(_metadata, self->pmdsize, variant->thp_policy); + + wait(&ret); + if (WIFEXITED(ret)) + ret = WEXITSTATUS(ret); + else + ret = -EINVAL; + ASSERT_EQ(ret, 0); +} + +TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/mm/thp_settings.c b/tools/testing/selftests/mm/thp_settings.c index bad60ac52874a..574bd0f8ae480 100644 --- a/tools/testing/selftests/mm/thp_settings.c +++ b/tools/testing/selftests/mm/thp_settings.c @@ -382,10 +382,17 @@ unsigned long thp_shmem_supported_orders(void) return __thp_supported_orders(true); } -bool thp_is_enabled(void) +bool thp_available(void) { if (access(THP_SYSFS, F_OK) != 0) return false; + return true; +} + +bool thp_is_enabled(void) +{ + if (!thp_available()) + return false; int mode = thp_read_string("enabled", thp_enabled_strings); diff --git a/tools/testing/selftests/mm/thp_settings.h b/tools/testing/selftests/mm/thp_settings.h index 6c07f70beee97..76eeb712e5f10 100644 --- a/tools/testing/selftests/mm/thp_settings.h +++ b/tools/testing/selftests/mm/thp_settings.h @@ -84,6 +84,7 @@ void thp_set_read_ahead_path(char *path); unsigned long thp_supported_orders(void); unsigned long thp_shmem_supported_orders(void); +bool thp_available(void); bool thp_is_enabled(void); #endif /* __THP_SETTINGS_H__ */ -- 2.47.3