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

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Date:	Tue, 15 Jul 2014 20:21:52 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, Tejun Heo <tj@...nel.org>,
	Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 13/13] mm: memcontrol: rewrite uncharge API

On Tue 15-07-14 13:34:39, Johannes Weiner wrote:
> On Tue, Jul 15, 2014 at 06:07:35PM +0200, Michal Hocko wrote:
> > On Tue 15-07-14 11:55:37, Naoya Horiguchi wrote:
> > > On Wed, Jun 18, 2014 at 04:40:45PM -0400, Johannes Weiner wrote:
> > > ...
> > > > diff --git a/mm/swap.c b/mm/swap.c
> > > > index a98f48626359..3074210f245d 100644
> > > > --- a/mm/swap.c
> > > > +++ b/mm/swap.c
> > > > @@ -62,6 +62,7 @@ static void __page_cache_release(struct page *page)
> > > >  		del_page_from_lru_list(page, lruvec, page_off_lru(page));
> > > >  		spin_unlock_irqrestore(&zone->lru_lock, flags);
> > > >  	}
> > > > +	mem_cgroup_uncharge(page);
> > > >  }
> > > >  
> > > >  static void __put_single_page(struct page *page)
> > > 
> > > This seems to cause a list breakage in hstate->hugepage_activelist
> > > when freeing a hugetlbfs page.
> > 
> > This looks like a fall out from
> > http://marc.info/?l=linux-mm&m=140475936311294&w=2
> > 
> > I didn't get to review this one but the easiest fix seems to be check
> > HugePage and do not call uncharge.
> 
> Yes, that makes sense.  I'm also moving the uncharge call into
> __put_single_page() and __put_compound_page() so that PageHuge(), a
> function call, only needs to be checked for compound pages.

Hmm, there doesn't seem to be any point in calling __page_cache_release
for HugePage as well. So it should be sufficient that
__put_compound_page doesn't call __page_cache_release for PageHuge and
uncharge can stay there. Maybe this would be slightly better...
-- 
Michal Hocko
SUSE Labs
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