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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1t1QQG-0000000B8OA-2MSF; Thu, 17 Oct 2024 13:20:12 +0000 Date: Thu, 17 Oct 2024 14:20:12 +0100 From: Matthew Wilcox To: lizhe.67@bytedance.com Cc: akpm@linux-foundation.org, boqun.feng@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, longman@redhat.com, mingo@redhat.com, peterz@infradead.org, will@kernel.org Subject: Re: [RFC 2/2] khugepaged: use upgrade_read() to optimize collapse_huge_page Message-ID: References: <20241017061841.81240-1-lizhe.67@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241017061841.81240-1-lizhe.67@bytedance.com> X-Stat-Signature: cgaxxktjagunb1t1bxiidoj3sma7jdry X-Rspamd-Queue-Id: 34643C0025 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1729171207-62891 X-HE-Meta: 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 i5v08gyU c5usWkXqOAAYNIbGwyYYCXrQSOF6MywV0O+VK7q/6GV/+eeBDdn7Hjw17yNPanjwZatxiGoUwFI4CN4Tu7Nly7EFCVnHkDZLWr5Ru5Xsu70E6qN0Gklaj0J3UGXJ4hUYxNMouZcY1IYtwR936cZtAufauLeCAVLWoBTFWcJohfv4zwMB4CaLRvXSUsonqa4H1DUKvyHSkwX8VM3QzAzkzUT+IcuWTzJ0z9ED7e2o27W7GzOkAII6OgXiOT8ERrk01tqdrDPqzykslEQ+5djIqYNVWsbF5fzdFN41zMI4WB7umd6XTSrRjkV4/VR4f0tiHoIVSRQHgmaY29v150fGFfIMSfWEBeBuah2wFDdl4v7uSuw+zWG/93P6HN8FEvhPDcHwiOfFiVKBwjme+1zKJy8q/4nvl9Y3NcKTxjI2eYsTGX1A= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Thu, Oct 17, 2024 at 02:18:41PM +0800, lizhe.67@bytedance.com wrote: > On Wed, 16 Oct 2024 12:53:15 +0100, willy@infradead.org wrote: > > >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. > > Yes, I will add the relevant data to v2 patch. How about telling us all now so we know whether to continue discussing this?