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Fri, 06 Nov 2026 05:26:09 -0800 (PST) Received: from localhost.localdomain ([240e:b8f:1df9:a600:c693:b19f:ada0:748]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b0b323a1fdsm7888529a91.5.2026.11.06.05.26.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Nov 2026 05:26:09 -0800 (PST) Date: Fri, 6 Nov 2026 21:26:01 +0800 From: Vernon Yang 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 Subject: Re: [PATCH v2 3/3] mm/khugepaged: release contended mmap read lock after scanning enough VMAs Message-ID: <798cd192-9ec2-4f37-9cba-44db275a269c@gmail.com> References: <20261105-khugepaged-latency-fix-v2-0-4384bbfe4606@kernel.org> <20261105-khugepaged-latency-fix-v2-3-4384bbfe4606@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: fedyuyf6zmpbuemzkaifc7z9w3bqms5b X-Rspamd-Queue-Id: A78F81A0008 X-Rspam-User: X-Rspamd-Server: rspam08 X-Spam-Status: No, score=-2.8 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 autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1793971570-594088 X-HE-Meta: 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 gekImwti iRaj5qYy//po/46a9TMpzazH1+PWizLf0qy98jwscUKpep+AfLPEnLsyOplB3tX44VN0rADaEAcF0Uto4IkLyIju4j/m4xZVxBBXktP7sr295wlWrWotQX7ZUTUI0eUzSB/cG7Y1IXtzAESDAtzyOYTgGPIiVftEYP0xe30xCq99WUSGJZ7Q1NAOlm7s0tfxE2wlcdOQwRoG9Xd6rmMc3Xl/DIRUV25kKADSwZfyPEfNf6MJJz9eg6WCUyqw3D7nh3ZIzCxqUhmtEjv1hachkoAmoms/GWm40t21L9TH+VcN48abBZQgtQrmeB+ECQkC4TXqq+cwvojCQek8NvkDCGzoes6O/+xyQRt+mYgZhG2kEwo/xJTUTZs7BwCKARhr01wevZPcjISUCAXpHcluF4MBKlzBYHjJFdUs5GT9jW6DZDcwIlP2aPb7DWQTGHu9vMDugACSn/JcMdxNRq5osdKtLFmsfElskvF9a 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 12:07:53PM +0000, Lorenzo Stoakes (ARM) wrote: > On reflection, I think this would be better implemented as something like: > > static void collapse_scan_mm_slot(unsigned int progress_max, ...) > { > unsigned int long lock_start = jiffies; > ... > for_each_vma(vmi, vma) { > ... > if (time_after(jiffies, lock_start) && mmap_lock_is_contended(mm)) { > mmap_read_unlock(mm); > cond_resched(); > mmap_read_lock(mm); > lock_start = jiffies; > vma_iter_set(&vmi, mm_slot->address); > continue; > } > } > } > > Which avoids magic numbers, and means if we hold the lock for 1-10ms (depending > on HZ), which is a long time in the kernel to hold a lock, AND the lock is > contended, we drop/reacquire. Looks good to me. Is the test result of this solution the same as the current one? -- Cheers, Vernon