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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 v7 2/3] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper Message-ID: References: <20260921-fix_split-v7-0-d25ec991159f@arm.com> <20260921-fix_split-v7-2-d25ec991159f@arm.com> <36465f31-59e2-43a5-8cd8-f8bb1844da3c@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 1DEEE1C0002 X-Stat-Signature: 56ndntcbd6ytysfmi3o9q14oa9c11fzb X-Rspamd-Server: rspam01 X-HE-Tag: 1790060422-62764 X-HE-Meta: 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 dhZz1kuA w8XcgKUocoDRRMbdfxjRHvUJls0+YzN5psEcupFm8jSyLPW5MY8kVS/0+hY4KLi9AjB3yKdWwCZdYngMxpqqHQXQ87VEIzxQE/aBotDoZxZL1o880mOY2TSzH1li0ZSrOLHCwX9ROPjyzRTc1vVvGJX6W2fYYMkla5U0rbrKkzbLco7t+GUp0uveNNIJ5xbs/8yu7EU6E/d6lArhlfSkaQDiPuFOzZDNRuu7PDMTM/uUjFlVno+NEDlSfR+oEJHjCjiXCHsbhwtWcYFWE6N90xCAbfMKalM+LQnMo6gXK0libwi3jmm/ykJdcseyiWs7/2faYT9UWtT+V2p8Zc/52tnkFiAIhlKRJA+tl Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 21, 2026 at 11:05:15PM +0200, David Hildenbrand (Arm) wrote: > On 9/21/26 20:48, Yeoreum Yun wrote: > > Hi, > > > >> On 9/21/26 12:40, 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. > >>> > >>> Since shmem pages are also file-backed, simply check whether the page > >>> is file-backed. > >>> > >>> Suggested-by: David Hildenbrand (Arm) > >>> Suggested-by: Zi Yan > >> > >> Do we need a Fixes: tag? > > > > Since this change is required for the chaning of behavior of glibc, > > I don't think we don't need to add Fixes tag in here? > > > Our test made wrong assumptions on the underlying behavior of the user space > allocator (no VMA merging would happen). So I'd argue that we should add a > Fixes: for the test. Okay. while I do - add intermediate patch before this as you suggeeted. - on the intermediate patch, add fix tag. - based the patch, rebase this patch to add anon/file check for other check_large_folios() type. Thanks. > > -- > Cheers, > > David -- Sincerely, Yeoreum Yun