linux-kernel - Re: [PATCH v2 3/7] memcg: reduce memory for the lruvec and memcg stats

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Message-ID: <CAJD7tkbj1hdka1wJiRZA+nOXFb3YW3adN=CENp2F+FACm7N+Tg@mail.gmail.com>
Date: Fri, 26 Apr 2024 18:18:50 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/7] memcg: reduce memory for the lruvec and memcg stats

On Fri, Apr 26, 2024 at 6:16 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
>
> On Fri, Apr 26, 2024 at 05:51:23PM -0700, Yosry Ahmed wrote:
> > On Fri, Apr 26, 2024 at 5:37 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> > >
> > > At the moment, the amount of memory allocated for stats related structs
> > > in the mem_cgroup corresponds to the size of enum node_stat_item.
> > > However not all fields in enum node_stat_item has corresponding memcg
> > > stats. So, let's use indirection mechanism similar to the one used for
> > > memcg vmstats management.
> >
> > Just curious, does the indirection table cause any noticeable
> > performance impact? My guess is no, but the update paths are usually
> > very performance sensitive.
> >
> > I guess lkp will shout at us if there are any noticeable regressions.
>
> Yeah and that is the reason I made the indirection table smaller (i.e.
> int8_t) to keep more entries in a single cacheline.

Thanks for pointing this out, probably worth including in the commit log :)