From: Michal Hocko <mhocko@suse.com> To: Vaibhav Jain <vaibhav@linux.ibm.com> Cc: cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>, Johannes Weiner <hannes@cmpxchg.org>, Jonathan Corbet <corbet@lwn.net>, Vladimir Davydov <vdavydov.dev@gmail.com>, Andrew Morton <akpm@linux-foundation.org>, "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>, Shakeel Butt <shakeelb@google.com>, Yosry Ahmed <yosryahmed@google.com> Subject: Re: [PATCH] memcg: provide reclaim stats via 'memory.reclaim' Date: Fri, 20 May 2022 09:29:44 +0200 [thread overview] Message-ID: <YodDaFVeU33bu7yQ@dhcp22.suse.cz> (raw) In-Reply-To: <87zgjcg4xs.fsf@vajain21.in.ibm.com> On Fri 20-05-22 10:45:43, Vaibhav Jain wrote: > > Thanks for looking into this patch Michal, > > Michal Hocko <mhocko@suse.com> writes: > > > On Thu 19-05-22 04:08:15, Vaibhav Jain wrote: > >> [1] Provides a way for user-space to trigger proactive reclaim by introducing > >> a write-only memcg file 'memory.reclaim'. However reclaim stats like number > >> of pages scanned and reclaimed is still not directly available to the > >> user-space. > >> > >> This patch proposes to extend [1] to make the memcg file 'memory.reclaim' > >> readable which returns the number of pages scanned / reclaimed during the > >> reclaim process from 'struct vmpressure' associated with each memcg. This should > >> let user-space asses how successful proactive reclaim triggered from memcg > >> 'memory.reclaim' was ? > >> > >> With the patch following command flow is expected: > >> > >> # echo "1M" > memory.reclaim > >> > >> # cat memory.reclaim > >> scanned 76 > >> reclaimed 32 > > > > Why cannot you use memory.stat? Sure it would require to iterate over > > the reclaimed hierarchy but the information about scanned and reclaimed > > pages as well as other potentially useful stats is there. > > Agree that "memory.stat" is more suitable for scanned/reclaimed stats as > it already is exposing bunch of other stats. > > The discussion on this patch however seems to have split into two parts: > > 1. Is it a good idea to expose nr_scanned/nr_reclaimed to users-space > and if yes how ? > > IMHO, I think it will be better to expose this info via 'memory.stat' as it > can be useful insight into the reclaim efficiency and vmpressure. We already do that with some more metrics pgrefill 9801926 pgscan 27329762 pgsteal 22715987 pgactivate 250691267 pgdeactivate 9521843 pglazyfree 0 pglazyfreed 0 > 2. Will it be useful to provide feedback to userspace when it writes to > 'memory.reclaim' on how much memory has been reclaimed ? > > IMHO, this will be a useful feeback to userspace to better adjust future > proactive reclaim requests via 'memory.reclaim' How precise this information should be? A very simplistic approach would be cp memory.stat stats.before echo $WHATEVER > memory.reclaim cp memory.stat stats.after This will obviously contain also activity outside of the explicitly triggered reclaim (racing background/direct reclaim) but isn't that what actually matters? Are there any cases where the only metric you care about is the triggered reclaim in isolation? -- Michal Hocko SUSE Labs
WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> To: Vaibhav Jain <vaibhav-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org> Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Jonathan Corbet <corbet-T1hC0tSOHrs@public.gmane.org>, Vladimir Davydov <vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, "Aneesh Kumar K . V" <aneesh.kumar-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>, Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Yosry Ahmed <yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> Subject: Re: [PATCH] memcg: provide reclaim stats via 'memory.reclaim' Date: Fri, 20 May 2022 09:29:44 +0200 [thread overview] Message-ID: <YodDaFVeU33bu7yQ@dhcp22.suse.cz> (raw) In-Reply-To: <87zgjcg4xs.fsf-+lRoeRASfQgA+286u2LMdEEOCMrvLtNR@public.gmane.org> On Fri 20-05-22 10:45:43, Vaibhav Jain wrote: > > Thanks for looking into this patch Michal, > > Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> writes: > > > On Thu 19-05-22 04:08:15, Vaibhav Jain wrote: > >> [1] Provides a way for user-space to trigger proactive reclaim by introducing > >> a write-only memcg file 'memory.reclaim'. However reclaim stats like number > >> of pages scanned and reclaimed is still not directly available to the > >> user-space. > >> > >> This patch proposes to extend [1] to make the memcg file 'memory.reclaim' > >> readable which returns the number of pages scanned / reclaimed during the > >> reclaim process from 'struct vmpressure' associated with each memcg. This should > >> let user-space asses how successful proactive reclaim triggered from memcg > >> 'memory.reclaim' was ? > >> > >> With the patch following command flow is expected: > >> > >> # echo "1M" > memory.reclaim > >> > >> # cat memory.reclaim > >> scanned 76 > >> reclaimed 32 > > > > Why cannot you use memory.stat? Sure it would require to iterate over > > the reclaimed hierarchy but the information about scanned and reclaimed > > pages as well as other potentially useful stats is there. > > Agree that "memory.stat" is more suitable for scanned/reclaimed stats as > it already is exposing bunch of other stats. > > The discussion on this patch however seems to have split into two parts: > > 1. Is it a good idea to expose nr_scanned/nr_reclaimed to users-space > and if yes how ? > > IMHO, I think it will be better to expose this info via 'memory.stat' as it > can be useful insight into the reclaim efficiency and vmpressure. We already do that with some more metrics pgrefill 9801926 pgscan 27329762 pgsteal 22715987 pgactivate 250691267 pgdeactivate 9521843 pglazyfree 0 pglazyfreed 0 > 2. Will it be useful to provide feedback to userspace when it writes to > 'memory.reclaim' on how much memory has been reclaimed ? > > IMHO, this will be a useful feeback to userspace to better adjust future > proactive reclaim requests via 'memory.reclaim' How precise this information should be? A very simplistic approach would be cp memory.stat stats.before echo $WHATEVER > memory.reclaim cp memory.stat stats.after This will obviously contain also activity outside of the explicitly triggered reclaim (racing background/direct reclaim) but isn't that what actually matters? Are there any cases where the only metric you care about is the triggered reclaim in isolation? -- Michal Hocko SUSE Labs
next prev parent reply other threads:[~2022-05-20 7:29 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-05-18 22:38 [PATCH] memcg: provide reclaim stats via 'memory.reclaim' Vaibhav Jain 2022-05-18 22:46 ` Yosry Ahmed 2022-05-19 8:50 ` Vaibhav Jain 2022-05-19 18:22 ` Yosry Ahmed 2022-05-19 5:08 ` Shakeel Butt 2022-05-19 9:41 ` Vaibhav Jain 2022-05-19 7:59 ` Greg Thelen 2022-05-19 9:56 ` Vaibhav Jain 2022-05-19 11:02 ` Michal Hocko 2022-05-19 11:02 ` Michal Hocko 2022-05-20 5:15 ` Vaibhav Jain 2022-05-20 7:29 ` Michal Hocko [this message] 2022-05-20 7:29 ` Michal Hocko 2022-05-23 22:50 ` Yosry Ahmed 2022-05-24 11:45 ` Johannes Weiner 2022-05-24 19:01 ` Yosry Ahmed 2022-05-25 8:59 ` Michal Hocko 2022-05-25 8:59 ` Michal Hocko 2022-05-25 20:31 ` Yosry Ahmed
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