linux-kernel - Re: [PATCH] Revert "mm:vmscan: fix inaccurate reclaim during proactive reclaim"

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Date: Fri, 26 Jan 2024 08:41:30 -0800
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Michal Hocko <mhocko@...e.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Shakeel Butt <shakeelb@...gle.com>, Muchun Song <muchun.song@...ux.dev>, 
	Andrew Morton <akpm@...ux-foundation.org>, android-mm@...gle.com, yuzhao@...gle.com, 
	yangyifei03@...ishou.com, cgroups@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "mm:vmscan: fix inaccurate reclaim during
 proactive reclaim"

On Fri, Jan 26, 2024 at 8:34 AM Johannes Weiner <hannes@...xchg.org> wrote:
>
> On Wed, Jan 24, 2024 at 09:46:23AM -0800, T.J. Mercier wrote:
> > In the meantime, instead of a revert how about changing the batch size
> > geometrically instead of the SWAP_CLUSTER_MAX constant:
> >
> >                 reclaimed = try_to_free_mem_cgroup_pages(memcg,
> > -                                       min(nr_to_reclaim -
> > nr_reclaimed, SWAP_CLUSTER_MAX),
> > +                                       (nr_to_reclaim - nr_reclaimed)/2,
> >                                         GFP_KERNEL, reclaim_options);
> >
> > I think that should address the overreclaim concern (it was mentioned
> > that the upper bound of overreclaim was 2 * request), and this should
> > also increase the reclaim rate for root reclaim with MGLRU closer to
> > what it was before.
>
> Hahaha. Would /4 work for you?
>
> I genuinely think the idea is worth a shot. /4 would give us a bit
> more margin for error, since the bailout/fairness cutoffs have changed
> back and forth over time. And it should still give you a reasonable
> convergence on MGLRU.
>
> try_to_free_reclaim_pages() already does max(nr_to_reclaim,
> SWAP_CLUSTER_MAX) which will avoid the painful final approach loops
> the integer division would produce on its own.
>
> Please add a comment mentioning the compromise between the two reclaim
> implementations though.

I'll try it out and get back to you. :)