linux-kernel - Re: [PATCH v3] mm: memcg: Use larger batches for proactive reclaim

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Date: Sun, 4 Feb 2024 08:17:25 -0800
From: Shakeel Butt <shakeelb@...gle.com>
To: "T.J. Mercier" <tjmercier@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	Andrew Morton <akpm@...ux-foundation.org>, Efly Young <yangyifei03@...ishou.com>, 
	android-mm@...gle.com, yuzhao@...gle.com, mkoutny@...e.com, 
	Yosry Ahmed <yosryahmed@...gle.com>, cgroups@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm: memcg: Use larger batches for proactive reclaim

On Fri, Feb 2, 2024 at 3:39 PM T.J. Mercier <tjmercier@...gle.com> wrote:
>
> Before 388536ac291 ("mm:vmscan: fix inaccurate reclaim during proactive
> reclaim") we passed the number of pages for the reclaim request directly
> to try_to_free_mem_cgroup_pages, which could lead to significant
> overreclaim. After 0388536ac291 the number of pages was limited to a
> maximum 32 (SWAP_CLUSTER_MAX) to reduce the amount of overreclaim.
> However such a small batch size caused a regression in reclaim
> performance due to many more reclaim start/stop cycles inside
> memory_reclaim.
>
> Reclaim tries to balance nr_to_reclaim fidelity with fairness across
> nodes and cgroups over which the pages are spread. As such, the bigger
> the request, the bigger the absolute overreclaim error. Historic
> in-kernel users of reclaim have used fixed, small sized requests to
> approach an appropriate reclaim rate over time. When we reclaim a user
> request of arbitrary size, use decaying batch sizes to manage error while
> maintaining reasonable throughput.
>
> root - full reclaim       pages/sec   time (sec)
> pre-0388536ac291      :    68047        10.46
> post-0388536ac291     :    13742        inf
> (reclaim-reclaimed)/4 :    67352        10.51
>
> /uid_0 - 1G reclaim       pages/sec   time (sec)  overreclaim (MiB)
> pre-0388536ac291      :    258822       1.12            107.8
> post-0388536ac291     :    105174       2.49            3.5
> (reclaim-reclaimed)/4 :    233396       1.12            -7.4
>
> /uid_0 - full reclaim     pages/sec   time (sec)
> pre-0388536ac291      :    72334        7.09
> post-0388536ac291     :    38105        14.45
> (reclaim-reclaimed)/4 :    72914        6.96
>
> Fixes: 0388536ac291 ("mm:vmscan: fix inaccurate reclaim during proactive reclaim")
> Signed-off-by: T.J. Mercier <tjmercier@...gle.com>
> Reviewed-by: Yosry Ahmed <yosryahmed@...gle.com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
>

Acked-by: Shakeel Butt <shakeelb@...gle.com>