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[2003:d8:2f44:3700:be07:9a67:67f7:24e6]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-458a99ce1d2sm415915e9.23.2025.07.31.12.42.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 31 Jul 2025 12:42:32 -0700 (PDT) Message-ID: <7b13d8b5-a534-47f8-b6c5-09a65bffc691@redhat.com> Date: Thu, 31 Jul 2025 21:42:30 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 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: <20250731122825.2102184-1-usamaarif642@gmail.com> <20250731122825.2102184-5-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 31.07.25 14:27, Usama Arif wrote: > 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). > > 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 > 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 > --- [...] Looks much better already. Some quirks. > +#include > +#include > +#include > +#include > +#include > +#include > +#include > + > +#include "../kselftest_harness.h" > +#include "thp_settings.h" > +#include "vm_util.h" > + > +static int sz2ord(size_t size, size_t pagesize) > +{ > + return __builtin_ctzll(size / pagesize); > +} > + > +enum thp_collapse_type { > + THP_COLLAPSE_NONE, > + THP_COLLAPSE_MADV_HUGEPAGE, /* MADV_HUGEPAGE before access */ > + THP_COLLAPSE_MADV_COLLAPSE, /* MADV_COLLAPSE after access */ > +}; > + > +enum thp_policy { > + THP_POLICY_NEVER, > + THP_POLICY_MADVISE, > + THP_POLICY_ALWAYS, > +}; Couldn't you have reused "enum thp_enabled" end simply never specified the "THP_INHERIT"? Then, you need to do less translation. > + > +struct test_results { > + int prctl_get_thp_disable; The result is always one, does that here make sense? > + int prctl_applied_collapse_none; "prctl_applied" is a bit confusing. And most of these always have the same value. Can't we special case the remaining two cases on the current policy and avoid this struct compeltely? > + int prctl_applied_collapse_madv_huge; > + int prctl_applied_collapse_madv_collapse; > + int prctl_removed_collapse_none; > + int prctl_removed_collapse_madv_huge; > + int prctl_removed_collapse_madv_collapse; > +}; > + > +/* > + * 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); > + To avoid even mmap_mem to get merged with some other VMA, maybe just do before reading the smap here: /* HACK: make sure we have a separate VMA that we can check reliably. */ mprotect(mem, pmdsize, PROT_READ); or madvise(mem, pmdsize, MADV_DONTFORK); before reading smaps. That is probably the easiest approach. The you can drop the lengthy comment and perform a single thp check. [...] > + > +static void prctl_thp_disable_test(struct __test_metadata *const _metadata, > + size_t pmdsize, struct test_results *results) > +{ > + > + ASSERT_EQ(prctl(PR_GET_THP_DISABLE, NULL, NULL, NULL, NULL), > + results->prctl_get_thp_disable); > + > + /* tests after prctl overrides global policy */ > + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_NONE, pmdsize), > + results->prctl_applied_collapse_none); > + > + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_HUGEPAGE, pmdsize), > + results->prctl_applied_collapse_madv_huge); > + > + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_COLLAPSE, pmdsize), > + results->prctl_applied_collapse_madv_collapse); > + > + /* 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), > + results->prctl_removed_collapse_none); > + > + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_HUGEPAGE, pmdsize), > + results->prctl_removed_collapse_madv_huge); > + > + ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_COLLAPSE, pmdsize), > + results->prctl_removed_collapse_madv_collapse); > +} > + > +FIXTURE(prctl_thp_disable_completely) > +{ > + struct thp_settings settings; > + struct test_results results; Is this "expected_results" ? But again, hopefully we can remove that and instead just base it on the polocy that we configured. -- Cheers, David / dhildenb