linux-kernel - Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num

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Message-ID: <Z9sWlCQBchKlJ_hj@slm.duckdns.org>
Date: Wed, 19 Mar 2025 09:10:12 -1000
From: Tejun Heo <tj@...nel.org>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Johannes Weiner <hannes@...xchg.org>, Greg Thelen <gthelen@...gle.com>,
	Michal Koutný <mkoutny@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <edumzaet@...gle.com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num_cpu)

On Wed, Mar 19, 2025 at 06:35:02PM +0000, Yosry Ahmed wrote:
> On Wed, Mar 19, 2025 at 02:06:43PM -0400, Johannes Weiner wrote:
> > On Wed, Mar 19, 2025 at 05:16:02PM +0000, Yosry Ahmed wrote:
> > > @@ -365,9 +352,8 @@ __bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp)
> > >  void cgroup_rstat_flush_hold(struct cgroup *cgrp)
> > >  	__acquires(&cgroup_rstat_lock)
> > >  {
> > > -	might_sleep();
> > > +	cgroup_rstat_flush(cgrp);
> > >  	__cgroup_rstat_lock(cgrp, -1);
> > > -	cgroup_rstat_flush_locked(cgrp);
> > >  }
> > 
> > Might as well remove cgroup_rstat_flush_hold/release entirely? There
> > are no external users, and the concept seems moot when the lock is
> > dropped per default. cgroup_base_stat_cputime_show() can open-code the
> > lock/unlock to stabilize the counts while reading.
>  
> Yeah I missed the fact that the users are internal because the functions
> are not static. I also don't see the point of keeping them.
> 
> Tejun/Greg, should I send a patch on top of this one or do you prefer
> sending a new version?

Please send a patch on top.

Thanks.

-- 
tejun