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Thu, 29 Oct 2026 07:37:45 -0400 (EDT) Date: Thu, 29 Oct 2026 11:37:44 +0000 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org, Josef Bacik Subject: Re: [PATCH 05/46] mm/truncate: look again if a folio left the mapping Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-5-6f74bec9a5bb@kernel.org> <2f2ef336-2186-4f20-b7f5-565e60471bda@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f2ef336-2186-4f20-b7f5-565e60471bda@kernel.org> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A617A1C000E X-Stat-Signature: xbnm4nm17hxpsnuu84n56n1taf95e66f X-Rspam-User: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1793273883-782138 X-HE-Meta: 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 acSmQpJQ T4FkQzt55/dhj7oBbm0Y1cUuAfiKCPmhjFQOIbwPdAegcNEAQHoxsLA02rb/VvuB8l0kEmbm1v45uaimfwT5VQ+MGGHN1n0gRVap2/9Ea3JsYbVLceblWLMJVfUFQw2EQvwwG36k6USbQLqq4FROTx7+wsbqSh4finpClrIMXC15KRY0JxaUN9Z8jjEdHQIUdMFwHEt9RhqIKL2M45cWl6My8L5BN8CQzpPDvvuNyy7+wP6/xY0LZ2tLWMTSB9gZvFe5nVvQZbh1RdZ3+dVCrOg63pZqbQxcRTv5RkKEFGxjvOGakjZZ92lel4QE5F7kbsf5yrD1TPlwgQgCcSBqQ30KkEH7CKnZn3bdXKjq/b7Fsii1+fVnSF/GA+/5RI4YlImnA 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 Wed, Oct 28, 2026 at 10:45:34PM +0100, David Hildenbrand (Arm) wrote: > My brain hurts, does the above make sense? Yes, I missed that the loop only goes back to start when a lookup comes back empty below end. When the last batch reaches end, it exits without another look. It doesn't need the split either: any punch hole whose last page is in the page cache gets there. That exit looks unintended to me. b9a8a4195c7d ("truncate,shmem: Handle truncates that split large folios") turned the "if (start >= end) goto out" early exit into the loop condition. Before it, the loop went back to start until a lookup from start found nothing; Hugh kept that on purpose for hole punch in 792ceaefe621 ("mm/fs: fix pessimization in hole-punching pagecache"). Restoring it is enough, and makes the "restart to make sure all gone" comment true again: + if (start >= end) + return; + index = start; - while (index < end) { + for (;;) { Then a replaced folio is found on the next round, and truncate needs no special case for it. -- Kiryl Shutsemau / Kirill A. Shutemov