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[2003:d8:2f0a:ca00:f74f:2017:1617:3ec3]) by smtp.gmail.com with ESMTPSA id a13-20020adfeecd000000b002bbedd60a9asm13865885wrp.77.2023.01.31.00.32.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 Jan 2023 00:32:28 -0800 (PST) Message-ID: <040ed7a7-3f4d-dab7-5a49-1cd9933c5445@redhat.com> Date: Tue, 31 Jan 2023 09:32:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 To: Jens Axboe , David Howells , John Hubbard Cc: Al Viro , Christoph Hellwig , Matthew Wilcox , Jan Kara , Jason Gunthorpe , Logan Gunthorpe , Jeff Layton , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <3351099.1675077249@warthog.procyon.org.uk> <3520518.1675116740@warthog.procyon.org.uk> From: David Hildenbrand Organization: Red Hat Subject: Re: [GIT PULL] iov_iter: Improve page extraction (pin or just list) In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 83E261A001D X-Stat-Signature: 5p5zd6bnuj9q7yg9pqyzsh3mj1ib3d7w X-HE-Tag: 1675153955-440682 X-HE-Meta: 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 ApTHY4Et vDR7gcLFM1AX653XNl/3UjpDh3leSkUJ/6PCRRj8jptZLemoP8r7gz+UjD2zz6q5Ahh6IJRc5xflWTEdlzgZVmBbT0vj7WgcCnYkWLg60vDQuaQi3HHAJt8Gb1xNart2lIh9CDYEzSDISLij71qADAgmYM60KN/OXK/nWxVK/ZImvO9JVoxMaqpltWMjT5gbJtK2T4bu69/+yq71OXKvUTBFRhoMszgzNzMnNF1E8qXEtPtuX2uW534a/yPqP1/ZKznEP+k1Wn+5r3SvsTTehNOtheKEmZ0XUZHZldlRpeeMVbicnHNRf7QvGH9qB4SCjSVCVBmqEPGMEbknnerJbB4V3JWj3YYtT6+hdAg5JeNpXZTHbAEndgOpQ3WgvcDTyLw+q 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: On 30.01.23 23:15, Jens Axboe wrote: > On 1/30/23 3:12 PM, David Howells wrote: >> John Hubbard wrote: >> >>> This is something that we say when adding pin_user_pages_fast(), >>> yes. I doubt that I can quickly find the email thread, but we >>> measured it and weren't immediately able to come up with a way >>> to make it faster. >> >> percpu counters maybe - add them up at the point of viewing? > > They are percpu, see my last email. But for every 108 changes (on > my system), they will do two atomic_long_adds(). So not very > useful for anything but low frequency modifications. > Can we just treat the whole acquired/released accounting as a debug mechanism to detect missing releases and do it only for debug kernels? The pcpu counter is an s8, so we have to flush on a regular basis and cannot really defer it any longer ... but I'm curious if it would be of any help to only have a single PINNED counter that goes into both directions (inc/dec on pin/release), to reduce the flushing. Of course, once we pin/release more than ~108 pages in one go or we switch CPUs frequently it won't be that much of a help ... -- Thanks, David / dhildenb