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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , Kevin Brodsky , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 2/3] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper Message-ID: References: <20260907-fix_split-v5-0-822b810458bc@arm.com> <20260907-fix_split-v5-2-822b810458bc@arm.com> <956df69d-8c0a-420f-889e-7df2842605dc@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <956df69d-8c0a-420f-889e-7df2842605dc@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 6900A100008 X-Stat-Signature: tec9censythbeo4cjccuqonbfgwh9wct X-HE-Tag: 1789037660-189562 X-HE-Meta: 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 hBBBQvNh XGwdL/8t/i5/hdTZwmB0SKRIZS0xBHacu9FosgQv9yDdijD+PT7tzFsYRVfsIJA3QU8lZwgESoAOb1xlxurHLnsY6yBuhQT5ka32pHmIS3ZcKoNBAvz2ntLIoUM0fxsKxSTqxEvxl+XXGjujNLNYnWTinJdHQp419cDvUEjStFQRTXbyRh/EiSGooYku+BOi7o5+Prkl6EZRFS23CzcSm4G/tN4aMa5RBcbuZPETtVlNfEvYDW5CQ2R4zLhKlR+uaOsxTrV3j59MurqNFc5FD4U0jxF3XlZ+tNIM0vJrJg9LorfzJ0ybS5ZgJVFVZSZ5iAiZnD0C9rZqJdlC2MpUu1Pw56OD8n4tJcVacRgzXHoS1cEz7Q2LBtKoiVo5GgM/Fg5M3jBJuh+vnxl9QK3bn7x5kDJWkcyKqO3w2ChQEgBdtCeFtlGC7LdA/4g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On 9/7/26 10:19, Yeoreum Yun wrote: > > Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”), > > glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations > > made by memalign(). > > > > The underlying VMA may start at a different address from the aligned > > address returned by memalign(). Furthermore, a subsequent > > madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is > > already set. > > > > This causes split_huge_page_test to fail because the check_huge_xxx() > > helpers incorrectly require the address returned by memalign() to > > match the VMA start address reported in /proc/self/smaps. > > > > Instead of relying on /proc/self/smaps, use /proc/self/pagemap and > > /proc/kpageflags to detect huge-page mappings and large folios: > > > > 1. If hpage_size == pmd_pagesize, check PAGE_IS_HUGE instead of > > using check_large_folios(), since only the mapping type matters. > > This identifies PMD-mapped huge pages. > > 2. Otherwise, use check_large_folios() to detect large folios. This > > covers mTHP cases. > > 3. Check the folio flags according to the type of huge page. > > > > Suggested-by: David Hildenbrand (Arm) > > Suggested-by: Zi Yan > > Reviewed-by: Zi Yan > > Reviewed-by: Baolin Wang > > Tested-by: Baolin Wang > > Acked-by: Lorenzo Stoakes (ARM) > > Signed-off-by: Yeoreum Yun > > --- > > tools/testing/selftests/mm/vm_util.c | 145 ++++++++++++++++++++++------------- > > tools/testing/selftests/mm/vm_util.h | 1 + > > 2 files changed, 92 insertions(+), 54 deletions(-) > > > > diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c > > index 4821a3563036..dc62ce84e143 100644 > > [...] > > > > > - if (hpage_size == pmd_pagesize) > > - return __check_pmd_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size); > > +static bool check_huge_type(uint64_t categories, uint64_t kpageflags, > > + enum check_huge_type type) > > +{ > > + const bool file = categories & PAGE_IS_FILE; > > + const bool swapbacked = kpageflags & KPF_SWAPBACKED; > > + > > + switch (type) { > > + case CHECK_HUGE_ANON: > > + return !file; > > + case CHECK_HUGE_FILE: > > + return file && !swapbacked; > > + case CHECK_HUGE_SHMEM: > > + return file & swapbacked; > > + } > > Why do we even need CHECK_HUGE_SHMEM? > > That's really just a legacy thing for using smaps to identify huge pages. > > It's sufficient to identify CHECK_HUGE_FILE if you know that you have shmem mapping. > > You will not arbitrarily have non-shmem folios in a shmem mapping :) Agree. but there seems the case where discern whethr the mapping is with regular file or shmem like tmpfs -- khugepaged test where using __shmem_ops. So I think it would be better to keep this as-is. > > > > > - return check_large_folios(addr, len, nr_hpages, hpage_size); > > + return false; > > } > > > > -bool check_huge_file(void *addr, size_t len, int nr_hpages, uint64_t hpage_size) > > +static bool __check_huge(void *addr, size_t len, int nr_hpages, > > + uint64_t hpage_size, enum check_huge_type type) > > { > > - uint64_t pmd_pagesize = read_pmd_pagesize(); > > + bool ret = false; > > + int pagemap_fd, kpageflags_fd; > > + int nr_pmd_mappings = 0; > > + uint64_t pmd_pagesize, scan_mapping_size; > > + uint64_t categories, kpf; > > + unsigned long pfn; > > + bool check_pmd_mapping, allow_nonpresent; > > + char *start = addr; > > + char *end = start + len; > > > > + pmd_pagesize = read_pmd_pagesize(); > > if (!pmd_pagesize) > > ksft_exit_fail_msg("reading PMD pagesize failed\n"); > > > > - if (hpage_size == pmd_pagesize) > > - return __check_pmd_huge(addr, "FilePmdMapped:", nr_hpages, hpage_size); > > + check_pmd_mapping = (hpage_size == pmd_pagesize); > > + scan_mapping_size = (nr_hpages > 0) ? hpage_size : psize(); > > + /* Some mTHP tests check a partially populated PMD-sized range. */ > > + allow_nonpresent = (uint64_t)nr_hpages * hpage_size < len; > > > > - return check_large_folios(addr, len, nr_hpages, hpage_size); > > + pagemap_fd = open(PAGEMAP_PATH, O_RDONLY); > > + if (pagemap_fd < 0) > > + ksft_exit_fail_msg("open pagemap fail\n"); > > + > > + kpageflags_fd = open(KPAGEFLAGS_PATH, O_RDONLY); > > + if (kpageflags_fd < 0) { > > + close(pagemap_fd); > > No need to cleanup when exiting. Yes, but some test code does clean it up, so I was just confused about the convention :\ > > > + ksft_exit_fail_msg("open kpageflags fail\n"); > > + } > > + > > + if (!check_pmd_mapping && > > + !check_large_folios(pagemap_fd, kpageflags_fd, > > + addr, len, nr_hpages, hpage_size)) > > + goto out; > > + > > + for (; start < end; start += scan_mapping_size) { > > + categories = pagemap_scan_get_categories(pagemap_fd, start); > > + pfn = pagemap_get_pfn(pagemap_fd, start); > > + if (pfn == -1UL) { > > + if (!allow_nonpresent) > > + goto out; > > + else > > + continue; > > + } > > + if (pageflags_get(pfn, kpageflags_fd, &kpf)) > > + ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno)); > > + if (check_pmd_mapping && (categories & PAGE_IS_HUGE)) > > + nr_pmd_mappings++; > > + if (kpf & KPF_COMPOUND_TAIL) > > + continue; > > + if (!check_huge_type(categories, kpf, type)) > > + goto out; > > + } > > + > > + if (check_pmd_mapping && (nr_pmd_mappings != nr_hpages)) > > + goto out; > > + ret = true; > > + > > +out: > > + close(pagemap_fd); > > + close(kpageflags_fd); > > + return ret; > > } > > > > -- > Cheers, > > David > -- Sincerely, Yeoreum Yun