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Wed, 15 Jul 2026 10:08:16 -0400 (EDT) Date: Wed, 15 Jul 2026 15:08:15 +0100 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: akpm@linux-foundation.org, usama.anjum@collabora.com, peterx@redhat.com, liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shuah@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, stable@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v4] fs/proc/task_mmu: fix PAGEMAP_SCAN written state for PMD holes Message-ID: References: <20260713091710.206548-1-kirill@shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: F19BD100010 X-Rspam-User: X-Stat-Signature: 7p8owu4qyz5hhzi5k5mxm39pcx7qs4wq X-Rspamd-Server: rspam03 X-HE-Tag: 1784124499-310197 X-HE-Meta: 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 afTT1MPA rd9xGoGwVhUdW+8kEEx875LdURu6CCse6jYbUDRULmeACFNRtOkvukpNsJuo5TuoMh0oY50PNN57QfexmNZKsW1FO/sDb3XPDpGdrQbkoowYPvcU8MiEE2L3Lk1T444/tDAdoTIbuIBIWUN0FvLTuqJ8UVLRQToVtHCZ0IvXRdgwq0giKw2fYs+SNpwoEd7yQDj5abqJ6q4BB7rV7sAhTdHbkjG6MVI2OWhrQMX16nPSrHezlwtrF7kdPhSygj4luKQRaFOdtwZf3YZ+tV0tphN7m7fn9LwarI/eTEOsBlPkl/FFjWVf+6923zW5z30D8JC1B1Bu63qSrMJlSgXgCaMk6ULDpGZXdlgSLnbUcgdGSJEgKGRSntvQg0T0de/jA4bIiNLyPAxf2Z8V3g/6A9xEs4NBpwBYNXwXCztino9fySJQ0htuveEk1XvdIazE+nncUMnV6r+3sWUnb43C/QtrwH6atGIkyWEmV/cyedyyZpjM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 15, 2026 at 03:47:00PM +0200, David Hildenbrand (Arm) wrote: > > > > MADV_DONTNEED has fill-with-zeros semantics: it changes the contents of > > the range to zeroes (a subsequent read maps the zero page), which write > > Only in MAP_PRIVATE | MAP_ANON mappings. Right, I'll scope the fill-with-zeros wording to MAP_PRIVATE|MAP_ANON. The fix itself isn't anon-specific -- it covers any non-hugetlb uffd-wp VMA (anon and shmem); the invariant is just "unpopulated => written", matching pte_none in pagemap_page_category(). I'll spell that out, along with the WP_UNPOPULATED marker mechanism (a missing marker == the range was MADV_DONTNEED'd). > Do we really want to backport a test case? Usually we split them from the actual > fix. Agreed -- v5 will split it. The rest goes into v5: your shorter comment, reuse of unpopulated_scan_test()'s sequence, recover instead of ksft_exit on the mmap failure, and rename to unpopulated_thp_scan_test(). -- Kiryl Shutsemau / Kirill A. Shutemov