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Fri, 06 Nov 2026 02:49:23 -0800 (PST) Received: from [192.168.1.22] ([83.231.69.9]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b6e24012c3sm46488775e9.13.2026.11.06.02.49.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Nov 2026 02:49:22 -0800 (PST) Message-ID: <1188802c-3661-441d-85a7-3ac68042e022@gmail.com> Date: Fri, 6 Nov 2026 11:49:20 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/3] mm/khugepaged: release contended mmap read lock after scanning enough VMAs To: "Lorenzo Stoakes (ARM)" 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 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> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/6/26 11:33 AM, Lorenzo Stoakes (ARM) wrote: > 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. it wasn't my intention. I am bad at writing reviews, so AI assists me to reword it, so it's polished, and I still check all the output. now onward, maybe my reviews get a bit clumsy, and not polished. I will stop rewording them. -- cheers, jose a. p-a