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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <040ed7a7-3f4d-dab7-5a49-1cd9933c5445@redhat.com> References: <040ed7a7-3f4d-dab7-5a49-1cd9933c5445@redhat.com> <3351099.1675077249@warthog.procyon.org.uk> <3520518.1675116740@warthog.procyon.org.uk> To: David Hildenbrand Cc: dhowells@redhat.com, Jens Axboe , John Hubbard , 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 Subject: Re: [GIT PULL] iov_iter: Improve page extraction (pin or just list) MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3791871.1675172490.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Tue, 31 Jan 2023 13:41:30 +0000 Message-ID: <3791872.1675172490@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 X-Rspam-User: X-Rspamd-Queue-Id: DFC871C0015 X-Rspamd-Server: rspam01 X-Stat-Signature: 63qmgzc3knmjuj3r9woddgt3394zfnto X-HE-Tag: 1675172498-296177 X-HE-Meta: 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 rlVoRV6l l1wdolw54eTw3fUoajUkMZIdfVWpUH/CuvaHFg8r8Zf3P2hNuROzxeV1T+xqfcAuc4yOnOnwwKZZgv3IKN1zdCZnpNHwIyY77nRuchro1N72IfuKHklPsabLstCB443o0LElSQm8klBXNCHr22kVwWOTCeYuNz5GzhG06oiQwFd4hW6D3s/7DbKDPG/vcFzUh6fl91AwMk4qSpfrh1YDslRfnuZk6tyjpgInNEAd5wjgk/ZeWzdvvv/shFg== 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: David Hildenbrand wrote: > >> 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 mech= anism > 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 ca= nnot > really defer it any longer ... but I'm curious if it would be of any hel= p to > only have a single PINNED counter that goes into both directions (inc/de= c on > pin/release), to reduce the flushing. > = > Of course, once we pin/release more than ~108 pages in one go or we swit= ch > CPUs frequently it won't be that much of a help ... What are the stats actually used for? Is it just debugging, or do we actu= ally have users for them (control groups spring to mind)? David