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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-Archived-By: 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> X-Rspam-User: X-Rspamd-Queue-Id: B76D7100008 X-Stat-Signature: bpwkknq96wpnsqs1j4xfaz1fsamqikhe X-Rspamd-Server: rspam01 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793034933-494334 X-HE-Meta: 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 9l0mEwCH 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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