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From: "Michal Koutný" <mkoutny-IBi9RG/b67k@public.gmane.org>
To: Yosry Ahmed <yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Josef Bacik <josef-DigfWCa+lFGyeJad7bwFQA@public.gmane.org>,
	Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>,
	Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>,
	Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
	Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Roman Gushchin
	<roman.gushchin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org>,
	Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Muchun Song <muchun.song-fxUVXftIFDnyG1zEObXtfA@public.gmane.org>,
	Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Vasily Averin
	<vasily.averin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org>,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	bpf-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
Subject: Re: [PATCH v3 6/8] workingset: memcg: sleep when flushing stats in workingset_refault()
Date: Tue, 4 Apr 2023 18:53:05 +0200	[thread overview]
Message-ID: <20230404165305.ffs7uscqpndnfytn@blackpad> (raw)
In-Reply-To: <20230330191801.1967435-7-yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

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On Thu, Mar 30, 2023 at 07:17:59PM +0000, Yosry Ahmed <yosryahmed-hpIqsD4AKldhl2p70BpVqQ@public.gmane.orgm> wrote:
> In workingset_refault(), we call
> mem_cgroup_flush_stats_atomic_ratelimited() to read accurate stats
> within an RCU read section and with sleeping disallowed. Move the
> call above the RCU read section to make it non-atomic.
> 
> Flushing is an expensive operation that scales with the number of cpus
> and the number of cgroups in the system, so avoid doing it atomically
> where possible.

I understand why one does not process the whole flushing load in one go
in general.
However, I remember there were reports of workingset_refault() being
sensitive to latencies (hence the ratelimited call was created).

Is there any consideration on impact of this here?
(Or are there other cond_resched() precendents on this path? Should it
be mentioned like in the vmscan (7/8) commit?)

Thanks,
Michal

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  parent reply	other threads:[~2023-04-04 16:53 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-30 19:17 [PATCH v3 0/8] memcg: avoid flushing stats atomically where possible Yosry Ahmed
     [not found] ` <20230330191801.1967435-1-yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2023-03-30 19:17   ` [PATCH v3 1/8] cgroup: rename cgroup_rstat_flush_"irqsafe" to "atomic" Yosry Ahmed
2023-03-30 19:17   ` [PATCH v3 3/8] memcg: do not flush stats in irq context Yosry Ahmed
2023-03-30 19:18   ` [PATCH v3 7/8] vmscan: memcg: sleep when flushing stats during reclaim Yosry Ahmed
2023-03-30 19:18   ` [PATCH v3 8/8] memcg: do not modify rstat tree for zero updates Yosry Ahmed
2023-04-04 16:53     ` Michal Koutný
2023-03-30 19:17 ` [PATCH v3 2/8] memcg: rename mem_cgroup_flush_stats_"delayed" to "ratelimited" Yosry Ahmed
2023-03-30 19:17 ` [PATCH v3 4/8] memcg: replace stats_flush_lock with an atomic Yosry Ahmed
     [not found]   ` <20230330191801.1967435-5-yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2023-04-04 16:52     ` Michal Koutný
2023-04-04 17:13       ` Shakeel Butt
     [not found]         ` <CALvZod5Y+quOS1XQvVBTvv7FRs3455j_79f0GoR+FqCFzbwkuA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2023-04-04 17:21           ` Shakeel Butt
2023-04-04 17:32             ` Michal Koutný
2023-03-30 19:17 ` [PATCH v3 5/8] memcg: sleep during flushing stats in safe contexts Yosry Ahmed
2023-03-30 19:30   ` Johannes Weiner
2023-04-04 15:09   ` Johannes Weiner
2023-03-30 19:17 ` [PATCH v3 6/8] workingset: memcg: sleep when flushing stats in workingset_refault() Yosry Ahmed
     [not found]   ` <20230330191801.1967435-7-yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2023-04-04 16:53     ` Michal Koutný [this message]
2023-04-04 18:09       ` Yosry Ahmed
     [not found]         ` <CAJD7tkb-0rXL9V2TX-Ax-3OkwJPYx_GaOT4D=VCA60riit+dOw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2023-04-05  8:00           ` Michal Koutný
2023-04-05  8:02             ` Yosry Ahmed

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