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[2003:d8:2f0a:ca00:f74f:2017:1617:3ec3]) by smtp.gmail.com with ESMTPSA id x12-20020adfec0c000000b002b065272da2sm14989741wrn.13.2023.01.31.07.10.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 Jan 2023 07:10:21 -0800 (PST) Message-ID: <0361aae6-59b2-1bbc-5530-a5be587b8a59@redhat.com> Date: Tue, 31 Jan 2023 16:10:19 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [GIT PULL] iov_iter: Improve page extraction (pin or just list) To: Jens Axboe , 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> <7f8f2d0f-4bf2-71aa-c356-c78c6b7fd071@redhat.com> <028c959d-e52a-5d08-6ac6-004ecdb3e549@kernel.dk> From: David Hildenbrand Organization: Red Hat In-Reply-To: <028c959d-e52a-5d08-6ac6-004ecdb3e549@kernel.dk> 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: 7bit X-Rspamd-Queue-Id: 00482C0029 X-Stat-Signature: xb1penq6dtfunqa4d9xng9sia3dpz7z7 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1675177825-731741 X-HE-Meta: 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 MRVzSrJx Qzk5W1LFP/AAlOs6+lSWnKHj5qCU80jLjOKfAc7eUKYhCMfqNlouLbnBF3MjPRAtge6Qx72UlVwmzpWK3t9kHR1c5Kus7AIOtzYhRjWlt86XnGydL+mC0C6A6rS2jj/Kt+mrqto+L4D6IYWMLxOC7TgVYvnERes5ka8GOs+G5jO/YM/qXLB1vKnEsARfQLGCruB17HVDnnyYVmDEbjr9XwRBhcEukMxOxH4WwDBOW+k9KhhX8c1iJECK6maPDZBvNlNQzBw4fsKPzLOgAWCP0RhBssS3ELmK3s5RZHlYsk+/ZBXP88MdqSUE+wgzuYvDl7iGilhPEbvMkSj5MV+wWFBsmcf1t2C1pZS5urfuS+oiUdtvclXlHHCnOvpduA3LGgHCzwsIIZuGZyi6w7D9Y3kQI6q1i67nnwoNdqv8OvYGouUFeXDETxXuMHqCPDAAPVTEnPfakclzvN11ImlJv90elQNlY0PadcTan 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 31.01.23 16:04, Jens Axboe wrote: > On 1/31/23 8:02?AM, David Hildenbrand wrote: >> On 31.01.23 15:50, Jens Axboe wrote: >>> 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; >>> >> >> We might want to hide the counters completely by defining them only >> with CONFIG_DEBUG_VM. > > Are all of them debug aids only? If so, yes we should just have > node_stat_* under CONFIG_DEBUG_VM. > Rather only these 2. Smth like: diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 815c7c2edf45..a526964b65ce 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -196,8 +196,10 @@ enum node_stat_item { NR_WRITTEN, /* page writings since bootup */ NR_THROTTLED_WRITTEN, /* NR_WRITTEN while reclaim throttled */ NR_KERNEL_MISC_RECLAIMABLE, /* reclaimable non-slab kernel pages */ +#ifdef CONFIG_DEBUG_VM NR_FOLL_PIN_ACQUIRED, /* via: pin_user_page(), gup flag: FOLL_PIN */ NR_FOLL_PIN_RELEASED, /* pages returned via unpin_user_page() */ +#endif NR_KERNEL_STACK_KB, /* measured in KiB */ #if IS_ENABLED(CONFIG_SHADOW_CALL_STACK) NR_KERNEL_SCS_KB, /* measured in KiB */ diff --git a/mm/vmstat.c b/mm/vmstat.c index 1ea6a5ce1c41..5cbd9a1924bf 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1227,8 +1227,10 @@ const char * const vmstat_text[] = { "nr_written", "nr_throttled_written", "nr_kernel_misc_reclaimable", +#ifdef CONFIG_DEBUG_VM "nr_foll_pin_acquired", "nr_foll_pin_released", +#endif "nr_kernel_stack", #if IS_ENABLED(CONFIG_SHADOW_CALL_STACK) "nr_shadow_call_stack", -- Thanks, David / dhildenb