Re: [patch 13/13] mm: memcontrol: rewrite uncharge API

From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Hugh Dickins <hughd@google.com>, Tejun Heo <tj@kernel.org>,
	Vladimir Davydov <vdavydov@parallels.com>,
	linux-mm@kvack.org, cgroups@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [patch 13/13] mm: memcontrol: rewrite uncharge API
Date: Wed, 16 Jul 2014 10:57:36 -0400	[thread overview]
Message-ID: <20140716145736.GA9794@nhori.redhat.com> (raw)
In-Reply-To: <20140716141447.GY29639@cmpxchg.org>

On Wed, Jul 16, 2014 at 10:14:47AM -0400, Johannes Weiner wrote:
...
> > >  	free_hot_cold_page(page, false);
> > >  }
> > >  
> > > @@ -75,7 +75,10 @@ static void __put_compound_page(struct page *page)
> > >  {
> > >  	compound_page_dtor *dtor;
> > >  
> > > -	__page_cache_release(page);
> > > +	if (!PageHuge(page)) {
> > > +		__page_cache_release(page);
> > > +		mem_cgroup_uncharge_page(page);
> 
> I reverted all these mm/swap.c changes again as well.  Instead,
> mem_cgroup_uncharge() now does a preliminary check if the page is
> charged before it touches page->lru.
> 
> That should be much more robust: now the vetting whether a page is
> valid for memcg happens at charge time only, all other operations
> check first if a page is charged before doing anything else to it.
> 
> These two places should be the only ones that need fixing then:

This change also passed my testing, so the problem should be fixed.

Thanks,
Naoya Horiguchi