linux-kernel - Re: [PATCH 2/2] memcg: relocate charge moving from ->attach to ->post

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Message-ID: <20160425194249.GG7822@mtj.duckdns.org>
Date:	Mon, 25 Apr 2016 15:42:49 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Petr Mladek <pmladek@...e.com>, cgroups@...r.kernel.org,
	Cyril Hrubis <chrubis@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] memcg: relocate charge moving from ->attach to
 ->post_attach

Hello, Michal.

On Mon, Apr 25, 2016 at 10:25:42AM +0200, Michal Hocko wrote:
> > * move_charge_struct->mm is added and ->can_attach is now responsible
> >   for pinning and recording the target mm.  mem_cgroup_clear_mc() is
> >   updated accordingly.  This also simplifies mem_cgroup_move_task().
> > 
> > * mem_cgroup_move_task() is now called from ->post_attach instead of
> >   ->attach.
> 
> This looks much better than the previous quick&dirty workaround. Thanks
> for taking an extra step!
> 
> Sorry for being so pushy but shouldn't we at least document those
> callbacks which depend on cgroup_threadgroup_rwsem to never ever block
> on WQ directly or indirectly. Maybe even enforce they have to be
> non-blocking. This would be out of scope of this particular patch of
> course but it would fit nicely into the series.

Yeah, I'll look into whether I can annotate this dependency with
lockdep.  If that isn't doable, I'll document the requirements.
cgroup methods have changed a lot and need to be redocumented anyway.

Thanks.

-- 
tejun