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Mon, 12 Jan 2026 11:17:54 -0500 (EST) Date: Mon, 12 Jan 2026 16:17:49 +0000 From: Kiryl Shutsemau To: Gladyshev Ilya Cc: guohanjun@huawei.com, wangkefeng.wang@huawei.com, weiyongjun1@huawei.com, yusongping@huawei.com, leijitang@huawei.com, artem.kuzin@huawei.com, stepanov.anatoly@huawei.com, alexander.grubnikov@huawei.com, gorbunov.ivan@h-partners.com, akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, harry.yoo@oracle.com, willy@infradead.org, yuzhao@google.com, baolin.wang@linux.alibaba.com, muchun.song@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/2] mm: improve folio refcount scalability Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 537584000B X-Stat-Signature: efbqo7byeki1f1nqoaurusfaopdokwo9 X-Rspam-User: X-HE-Tag: 1768234680-218869 X-HE-Meta: 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 xeylCWHf Scl2yVA6GB0tMeeyONi/Q0j1UCst8oabD2ONiaAiCNsqmfwhRQ7wPCeixFZEqPEWSZlwKpywUhqMrtrYqppR185PCMRZKP2aO4lGbwDC90B3pYjhqMSmzts9HCXz4szhMQN7qe4j9gIT2WhRsBlYF+iwiKjrg9wjziYXcJdpa77sZ/9M1dd+AfqyoQuN0o3k7+f+BjB8G/wgKWF5Sr/dSDg52ipnPHpCIn9Ol35eBhtxs5JZPxOC+0lE3KiLLxupWxGUeZbWQro2rX3B/bXtiPIU76ld5j9UEZMRQbDiOqiGFcLdYr5nWnJFoWOJeEcM5mYlVpZdO+NFt87P8kCysm5S88SWRzzByPgGGbtKLmL1IGHP7ryygHHvPcdaYSaG4IryYdQ5IA4O42QI2aoFeCSZ9SL5AJgWG/aR44PVnfF6vuStwpaFFCj7jZT8nTpHPyixq 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 Mon, Jan 12, 2026 at 05:32:10PM +0300, Gladyshev Ilya wrote: > On 1/12/2026 2:49 PM, Kiryl Shutsemau wrote: > > On Mon, Jan 12, 2026 at 11:30:38AM +0300, Gladyshev Ilya wrote: > > > Gentle ping on this proposal > > > > I generally like the idea, but I would like to hear from folks who > > actually understand serialization. > > > > Also, do you have number for "a full CAS loop when the counter is > > approaching overflow" thing? > > > I am not sure that overflow is a real problem because you need a very > specific race condition over a long time to achieve it... Yes. But if the page is popular for pinning, GUP_PIN_COUNTING_BIAS can cut the "very long time" substantially. > But as a safeguard, everything lower than 2^31 - #max concurrent > accesses (~#num cpu) should work, so let's say 2^30 What I meant is when we put a branch/loop in the hot path, your performance numbers will likely not look as attractive. Am I wrong? -- Kiryl Shutsemau / Kirill A. Shutemov