linux-kernel - Re: [patch 7/9] mm: memcontrol: do not acquire page

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Message-ID: <20140528113328.GG9895@dhcp22.suse.cz>
Date:	Wed, 28 May 2014 13:33:28 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	linux-mm@...ck.org, Hugh Dickins <hughd@...gle.com>,
	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 7/9] mm: memcontrol: do not acquire page_cgroup lock for
 kmem pages

On Tue 27-05-14 15:53:42, Johannes Weiner wrote:
> On Fri, May 23, 2014 at 03:39:38PM +0200, Michal Hocko wrote:
[...]
> > >  	if (!PageCgroupUsed(pc))
> > >  		return;
> > >  
> > > -	lock_page_cgroup(pc);
> > > -	if (PageCgroupUsed(pc)) {
> > > -		memcg = pc->mem_cgroup;
> > > -		ClearPageCgroupUsed(pc);
> > > -	}
> > > -	unlock_page_cgroup(pc);
> > 
> > maybe add
> > 	WARN_ON_ONCE(pc->flags != PCG_USED);
> > 
> > to check for an unexpected flags usage in the kmem path?
> 
> There is no overlap between page types that use PCG_USED and those
> that don't.  What would be the value of adding this?

I meant it as an early warning that something bad is going on.

-- 
Michal Hocko
SUSE Labs
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