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Mon, 26 Oct 2026 13:15:30 -0400 (EDT) Date: Mon, 26 Oct 2026 17:15:29 +0000 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Gregory Price , Zi Yan , Joshua Hahn , Rakie Kim , Ying Huang , Johannes Weiner , Vladimir Davydov , Michal Hocko , Hugh Dickins , Baolin Wang , Lukas Czerner , Carlos Maiolino , Christian Brauner , Jan Kara , Daniel Verkamp , Jeff Xu , Muchun Song , Oscar Salvador , David Stevens , "Matthew Wilcox (Oracle)" , William Kucharski , Chris Li , Kairui Song , Nhat Pham , Miaohe Lin , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 10/16] mm/shmem: discard whole new large folios on fallocate rollback Message-ID: References: <20261026-fixes_shmem-v1-0-703206d5fa0c@kernel.org> <20261026-fixes_shmem-v1-10-703206d5fa0c@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261026-fixes_shmem-v1-10-703206d5fa0c@kernel.org> On Mon, Oct 26, 2026 at 10:40:43AM +0100, David Hildenbrand (Arm) wrote: > When undoing a failed fallocate(), shmem_undo_range() must discard each > newly allocated folio. Its second scan instead passes large > folios to truncate_inode_partial_folio(), which does not necessarily > discard the entire large folio, but instead tries splitting it to > discard only the requested range. > > For example, with huge=always, a failed allocation starting at offset > 4 KiB can leave page 0 allocated in an otherwise empty file. > > Discard the whole folio when unfalloc is set. Note that we enter this > path only for folios that are not uptodate, and can consequently be > dropped without losing any data. > > Fixes: 55ac8bbe358b ("mm/shmem: fix race in shmem_undo_range w/THP") > Cc: stable@vger.kernel.org > Signed-off-by: David Hildenbrand (Arm) Acked-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov