linux-kernel - Re: [PATCH 5/5] memcg: make memcg_rstat

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Message-ID: <7v2v2bwgd4jbprimygguwatdi6zhsvidibk2zlddkx7ksg3y6l@u3mlw5bw3tyt>
Date: Fri, 16 May 2025 08:34:21 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Vlastimil Babka <vbabka@...e.cz>
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>, 
	Alexei Starovoitov <ast@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Harry Yoo <harry.yoo@...cle.com>, Yosry Ahmed <yosry.ahmed@...ux.dev>, 
	Peter Zijlstra <peterz@...radead.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	bpf@...r.kernel.org, linux-mm@...ck.org, cgroups@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH 5/5] memcg: make memcg_rstat_updated nmi safe

On Fri, May 16, 2025 at 11:45:39AM +0200, Vlastimil Babka wrote:
> On 5/16/25 08:49, Shakeel Butt wrote:
> > memcg: convert stats_updates to atomic_t
> 
> You have two subjects, I guess delete the second one?

Oops I squashed the patch at the very end and forgot to fix this.

> 
> > Currently kernel maintains memory related stats updates per-cgroup to
> > optimize stats flushing. The stats_updates is defined as atomic64_t
> > which is not nmi-safe on some archs. Actually we don't really need 64bit
> > atomic as the max value stats_updates can get should be less than
> > nr_cpus * MEMCG_CHARGE_BATCH. A normal atomic_t should suffice.
> > 
> > Also the function cgroup_rstat_updated() is still not nmi-safe but there
> > is parallel effort to make it nmi-safe, so until then let's ignore it in
> > the nmi context.
> > 
> > Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Thanks a lot.