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Perez de Azpillaga" Cc: David Hildenbrand , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/3] mm/khugepaged: release contended mmap read lock after scanning enough VMAs Message-ID: References: <20261105-khugepaged-latency-fix-v2-0-4384bbfe4606@kernel.org> <20261105-khugepaged-latency-fix-v2-3-4384bbfe4606@kernel.org> <551892bd-d7ca-4c79-9c7b-9d3d08c913e4@gmail.com> <5c084ac1-930d-40c7-b6d0-b56673da9cf5@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5c084ac1-930d-40c7-b6d0-b56673da9cf5@gmail.com> X-Stat-Signature: cn6qtnojjsm1zdfcjxb56ainpeq5sqe3 X-Rspamd-Queue-Id: 7F244180003 X-Rspam-User: X-Rspamd-Server: rspam11 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: 1793961213-176609 X-HE-Meta: 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 li/PITKi 3GNASHinNdLX4Yl2eaRTgrMDSZahpEVGROUWSvF8SfsIsR6UNE/JszxxWt72f/6IPBXwX5/FwFlb/f1PbRiWvy8k3UPwqn1oY0tSiAqw+R3TRHoWLxZBMERLD9IU4//2A/aGFWTOmh0/eQkepjoDTpSRJvrnDHrBRORy9+Wnna1gG2ZoWV3EqjGlfJcYzwSTpkHZcfSU9gSqTFk0ptuy83oTx6DcrMFIrRli30Fuo7rbK8BBMdu7SF+QqkwKuesVv7A87 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 Fri, Nov 06, 2026 at 11:29:00AM +0100, Jose A. Perez de Azpillaga wrote: > >> with pages_to_scan below 4 the batch is 0, so under constant contention > >> we keep dropping the lock at the cursor and never scan anything, don't we? > > > > This feels like repackaged AI review... > > > > The mmap lock won't be eternally contended and if it is, with pages_to_scan > > under 4, I think that's fine. > > > > Alternatively could make that >= an == and the post-++ a pre-++ and the 0 will > > never be hit in this case. > > > > Or could have a minimum cap. > > with >= a minimum cap needs to be 2, since the cursor can stop at hend > inside the VMA we just scanned and the walk lands on it again after the > drop. with == only batch - 1 VMAs get scanned per cycle, so a batch of 1 > scans nothing, today's batch-0 loop at pages_to_scan 4..7, and a batch > of 2 hits the hend case. it's safe from 3 up. Please don't copy/paste LLM responses. I'm sure it's in good faith, but it's not helpful. I will run any changes through AI myself. -- Cheers, Lorenzo