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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1t12aZ-00000007pPm-3HfV; Wed, 16 Oct 2024 11:53:15 +0000 Date: Wed, 16 Oct 2024 12:53:15 +0100 From: Matthew Wilcox To: lizhe.67@bytedance.com Cc: peterz@infradead.org, mingo@redhat.com, will@kernel.org, longman@redhat.com, boqun.feng@gmail.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC 2/2] khugepaged: use upgrade_read() to optimize collapse_huge_page Message-ID: References: <20241016043600.35139-1-lizhe.67@bytedance.com> <20241016043600.35139-3-lizhe.67@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241016043600.35139-3-lizhe.67@bytedance.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A534680003 X-Stat-Signature: 1kjotpphi58k7d3dpxb1rq51gff6yi9d X-Rspam-User: X-HE-Tag: 1729079585-116233 X-HE-Meta: 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 L/EdCFRn 9gLxnyC2S4pjq+TAUG5AvCW7SIxhIS/6n4N6ALAzeu8/f4Y8KmNszagfd3uMuNw3FVJzerUzGOeYcn9v328sjCfBynbY8sAm2VRz2KkdshElrRK+bY2ejoeBomNGQTXCl6xJuDbiotvxOw+cqpfo8wn1GrKNtFOPZn82HxHD4Pq++vs6NQfvdy8hsMuCKuLo71xubOXmVUKzdUc9UpuyCGjP8Aa8mLHHf1XGYQLKVP69R7IUrZBsD+wINtpmeZz0x6yYyXdL/aBVWwqP9gnvJC8hjv8IAr6rmKFtDehlSs2p9Wei04bAAlPwzGPmU95joQq9je6qvMZcGygHQ3LoJ4qxSHPV3vpbXUSfWQG6xtWzpxb8vyd4yGAwpmg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000019, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 16, 2024 at 12:36:00PM +0800, lizhe.67@bytedance.com wrote: > From: Li Zhe > > In function collapse_huge_page(), we drop mmap read lock and get > mmap write lock to prevent most accesses to pagetables. There is > a small time window to allow other tasks to acquire the mmap lock. > With the use of upgrade_read(), we don't need to check vma and pmd > again in most cases. This is clearly a performance optimisation. So you must have some numebrs that justify this, please include them.