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

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Message-ID: <8114231b-ec06-44a9-9075-9ccf0809de4a@suse.cz>
Date: Fri, 16 May 2025 11:45:39 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Shakeel Butt <shakeel.butt@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: 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 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?

> 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>