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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vtISB-00000008roY-0Sne; Fri, 20 Feb 2026 04:49:23 +0000 Date: Fri, 20 Feb 2026 04:49:22 +0000 From: Matthew Wilcox To: "David Hildenbrand (Arm)" Cc: Dev Jain , lsf-pc@lists.linux-foundation.org, ryan.roberts@arm.com, catalin.marinas@arm.com, will@kernel.org, ardb@kernel.org, hughd@google.com, baolin.wang@linux.alibaba.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [LSF/MM/BPF TOPIC] Per-process page size Message-ID: References: <20260217145026.3880286-1-dev.jain@arm.com> <2e68ef61-dcf2-46b2-913f-14980a104faf@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2e68ef61-dcf2-46b2-913f-14980a104faf@kernel.org> X-Stat-Signature: 7pzwdoxe6qonfuaqbczj6b54rwexjgiu X-Rspam-User: X-Rspamd-Queue-Id: 486D21C000D X-Rspamd-Server: rspam01 X-HE-Tag: 1771562975-87795 X-HE-Meta: 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 k4Ya7b69 +QtDaE84YkbbzWjCAcCxET6yuguWNKqUPRfiQsRumLt8UPxrNDc4dNrA92h5RvhI0AK0KJ/Un9rXdHO4OI9Sl/is7PNTNtcKRAseKAB4DfR2EshRgPJAlpSPMx4BIZw5RVZDHqUjMGVqsKsN6DSTG9IZdawKfWU5/aKsmEtxrTsRzCU0fr0hPSRlv7wvZQdaioW+eRhZgNrHMwHUuJVHi0qnHW13PGKlXct3A8+ud8D+dre7pBiDzN5ka1EiNPIQY7wbl X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Feb 17, 2026 at 04:30:59PM +0100, David Hildenbrand (Arm) wrote: > In a private conversation I also raised that some situations might make it > impossible/hard to drop+re-read. > > One example I cam up with if a folio is simply long-term R/O pinned. But I > am also not quite sure how mlock might interfere here. > > So yes, I think the page cache is likely the one of the most > problematic/messy thing to handle. So what if we convert to max-supported-order the first time somebody calls mmap on a given file? Most files are never mmaped, so it won't affect them. And files that are mmaped are generally not written to. So there should not be much in the page cache for the common case. And if no pages from the file have been mmaped yet, they cannot be pinned or mlocked.