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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-Archived-By: 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 X-Stat-Signature: cbma4ps3qghqdee98yja53xrwsmpi5bi X-Rspamd-Queue-Id: 3249A20002 X-Rspam-User: X-Rspamd-Server: rspam11 X-Spam-Status: No, score=-4.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1793962165-208064 X-HE-Meta: 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 PES9+qgR PFH1mP+/bvIuQXwlV2BeDLdAJtGOqVnNfWafcWDJQX7/bLEPxCsbS6NGOCfu4dVFZO5z7UcUNUSxzWDiJDwtrjTZ8s7azLT5UNpUfZZ0X1gE/8LPbYoNuhdKBluVBWC7xz4pvUzCdn7grNSrP0JxfEGFzfJLg6UyBbAjlxWE0qxn1kJyvp8uxwnecBqZakd4rSqdv8QZ3EJYgHqKyMFH7SFV/81AMFAjUYx6M6VANrZ8G4qPNjH6+xn/xBHJERlpcX6X2bSf4+54oWWSOLha9oKdG4hkXJFuiRKpvpssyObe02Q5vfGHZxqWzs/Zzo7kuac5SjU/WuXjSRzwqKUp5BmNXUAdQ6CDxzQOg24vpELtvSmFMU2zuevIfweVJbvm9dDypWWEppNi1JmA19LBGYht6jrnR6mCwh2u3soGNdDq5VEYGW5idRpZKJqtm6DQwBIGu 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 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