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Tue, 31 Jan 2023 06:50:47 -0800 (PST) Message-ID: Date: Tue, 31 Jan 2023 07:50:45 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [GIT PULL] iov_iter: Improve page extraction (pin or just list) Content-Language: en-US To: David Hildenbrand , David Howells Cc: 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 References: <040ed7a7-3f4d-dab7-5a49-1cd9933c5445@redhat.com> <3351099.1675077249@warthog.procyon.org.uk> <3520518.1675116740@warthog.procyon.org.uk> <3791872.1675172490@warthog.procyon.org.uk> <88d50843-9aa6-7930-433d-9b488857dc14@redhat.com> From: Jens Axboe In-Reply-To: <88d50843-9aa6-7930-433d-9b488857dc14@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 138A51C000E X-Stat-Signature: shjz13ayibbcbh5n3r1r71khjymyh1kb X-HE-Tag: 1675176648-580865 X-HE-Meta: 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 wWtC3zoL swpbyyZ7hnQaHs48xfP33SxNMbZx0uM78xPIFYR1hH/3TnFRpChFtDr9YuSBIzPpgjHqGMgJct4x0s4vivLeswiu1Y4i5Khb/AXzvITDoF+vtx+JVnSPv0kNQ30Sc3eI9qOJwSQPTd8I92SNlrtMtXoY3m8LVStS4Kjp1gwoEq+ya+1XVeCZNK2AoMvi5sI15Jvh+93hOjj9XljCLdbhLFUtnxECtv7SzUpUVbImeHFqiD9aKwJiY2+T+6RtIAIF/eWZTF/fLZZSZqv7MHPu9CLPE8uLs2Ctn8DolLEi0dMqoXRJ9l0GzkkmQMDDSh/RtGsepp3nfV4KVzZWCPaVAuZ1tkTNv1ey238lt2xhMNI0KuevGLzJL/OwP7ntAcfaKr2+SYLg8be1rNLacn0/kF2mLXwBIIR/EmWUWu5yjN/X6s40FPTE6EUuakueUfe66kYeb40K4LXQljxuBJzy7Rh9RonhfehiVKXju 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 1/31/23 6:48?AM, David Hildenbrand wrote: > On 31.01.23 14:41, David Howells wrote: >> 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 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 ... >> >> What are the stats actually used for? Is it just debugging, or do we actually >> have users for them (control groups spring to mind)? > > As it's really just "how many pinning events" vs. "how many unpinning > events", I assume it's only for debugging. > > For example, if you pin the same page twice it would not get accounted > as "a single page is pinned". How about something like the below then? I can send it out as a real patch, will run a sanity check on it first but would be surprised if this doesn't fix it. diff --git a/mm/gup.c b/mm/gup.c index f45a3a5be53a..41abb16286ec 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -168,7 +168,9 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags) */ smp_mb__after_atomic(); +#ifdef CONFIG_DEBUG_VM node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs); +#endif return folio; } @@ -180,7 +182,9 @@ struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags) static void gup_put_folio(struct folio *folio, int refs, unsigned int flags) { if (flags & FOLL_PIN) { +#ifdef CONFIG_DEBUG_VM node_stat_mod_folio(folio, NR_FOLL_PIN_RELEASED, refs); +#endif if (folio_test_large(folio)) atomic_sub(refs, folio_pincount_ptr(folio)); else @@ -236,8 +240,9 @@ int __must_check try_grab_page(struct page *page, unsigned int flags) } else { folio_ref_add(folio, GUP_PIN_COUNTING_BIAS); } - +#ifdef CONFIG_DEBUG_VM node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1); +#endif } return 0; -- Jens Axboe