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Thu, 27 Aug 2026 10:33:28 -0400 (EDT) Date: Thu, 27 Aug 2026 15:33:27 +0100 From: Kiryl Shutsemau To: kasong@tencent.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Usama Arif , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Chris Li , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Shivam Kalra , Kairui Song Subject: Re: [PATCH v3 02/18] mm/huge_memory: fix rejection of swap cache folios with a mapping Message-ID: References: <20260821-swap-thp-cleanup-v3-0-9b43f5163238@tencent.com> <20260821-swap-thp-cleanup-v3-2-9b43f5163238@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260821-swap-thp-cleanup-v3-2-9b43f5163238@tencent.com> X-Stat-Signature: r15erbxz4cphg56rqkus8rerch6dthf9 X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 9D79640009 X-Rspam-User: X-HE-Tag: 1787841211-512637 X-HE-Meta: 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 NJLrvEXK 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Aug 21, 2026 at 02:55:15AM +0800, Kairui Song via B4 Relay wrote: > From: Kairui Song > > A folio in the swap cache cannot be split if it has a mapping (shmem). > The split code does a defensive check for this in > __folio_freeze_and_split_unmapped, after the folio ref has been frozen > and the NR_SHMEM_THPS/NR_FILE_THPS counters have been decremented. It > rejects the split and returns -EINVAL without unfreezing the folio or > restoring the counters. That error path is buggy: if it is ever taken, > it leaves the folio frozen and stuck, skews the counters, and fires > the VM_WARN_ON_ONCE_FOLIO for a state that is actually legitimate. If you are going to repost this, could you make "This error path is buggy" a new paragraph? > > Check for this case up front in folio_check_splittable and return > -EBUSY before any state is modified, so the split routine always backs > out cleanly. > > Also fix a bracket style issue that checkpatch.pl keeps complaining > about. > > Fixes: 00527733d0dc ("mm/huge_memory: add two new (not yet used) functions for folio_split()") > Fixes: 714b056c8321 ("mm/huge_memory: convert VM_BUG* to VM_WARN* in __folio_split") This is inert bug, right? I don't think we want the commit to be backported. I expect stable machinery to pick it up based on Fixes. Is there a way to express "not stable material" while keeping Fixes: in place? > Reviewed-by: Zi Yan > Signed-off-by: Kairui Song Reviewed-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov