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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> <798cd192-9ec2-4f37-9cba-44db275a269c@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <798cd192-9ec2-4f37-9cba-44db275a269c@gmail.com> X-Rspamd-Server: rspam06 X-Stat-Signature: 9b3d7ntmz8qgfajzwhthzrnmytetee48 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-Rspamd-Queue-Id: E1A012000E X-Rspam-User: X-HE-Tag: 1793978666-258360 X-HE-Meta: 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 yNZqoBAz qtMQ0tnUacy9+pfNp7J0F/W5xYm3qRoYWWZBhBvfQBYhUpRaipf3HNYfeKqafmSPHsJeToj/t25FldkmXFPiwzdurLGvBWiKn4X58nXMCBkWe9ma8TxhLygAEuJ3QKy1u7gjCKwaYgMZqf8cVIgmy4wAEsPinrl1oEs9gBZTHHF5G5/hl8jRedqGrylwmW7gmB4r3bIs+LbbRbLpn7O7P37XXyTNLjwnK4I8fqxXC+6dkiJG9iyACO3ymZDdlYw8iMN/b 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 09:26:01PM +0800, Vernon Yang wrote: > 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? Thanks! I will update the commit to reflect the changes. > > -- > Cheers, > Vernon -- Cheers, Lorenzo