linux-kernel - Re: [patch 2/2] mm: memcg: count pte references from every member of the reclaimed hierarchy

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Date:	Wed, 14 Mar 2012 18:53:55 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] mm: memcg: count pte references from every member of
 the reclaimed hierarchy

On Wed 14-03-12 17:21:29, Johannes Weiner wrote:
> On Wed, Mar 14, 2012 at 03:25:19PM +0100, Michal Hocko wrote:
> > On Tue 28-02-12 15:14:49, Johannes Weiner wrote:
> > [...]
> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index b4622fb..21004df 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -1044,17 +1044,23 @@ struct lruvec *mem_cgroup_lru_move_lists(struct zone *zone,
> > >   * Checks whether given mem is same or in the root_mem_cgroup's
> > >   * hierarchy subtree
> > >   */
> > > -static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> > > -		struct mem_cgroup *memcg)
> > > +bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> > > +				  struct mem_cgroup *memcg)
> > >  {
> > > -	bool ret;
> > > -
> > >  	if (root_memcg == memcg)
> > >  		return true;
> > >  	if (!root_memcg->use_hierarchy)
> > >  		return false;
> > > +	return css_is_ancestor(&memcg->css, &root_memcg->css);
> > > +}
> > > +
> > > +static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> > > +				       struct mem_cgroup *memcg)
> > > +{
> > > +	bool ret;
> > > +
> > >  	rcu_read_lock();
> > > -	ret = css_is_ancestor(&memcg->css, &root_memcg->css);
> > > +	ret = __mem_cgroup_same_or_subtree(root_memcg, memcg);
> > >  	rcu_read_unlock();
> > >  	return ret;
> > >  }
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index c631234..120646e 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -708,7 +708,8 @@ static enum page_references page_check_references(struct page *page,
> > >  	int referenced_ptes, referenced_page;
> > >  	unsigned long vm_flags;
> > >  
> > > -	referenced_ptes = page_referenced(page, 1, mz->mem_cgroup, &vm_flags);
> > > +	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
> > > +					  &vm_flags);
> > >  	referenced_page = TestClearPageReferenced(page);
> > 
> > Maybe a stupid question but isn't target_mem_cgroup NULL in the global
> > reclaim case? And we doesn't handle that in __mem_cgroup_same_or_subtree...
> 
> It's intentional, page_referenced() does not call into same_or_subtree
> if the group is NULL.  As a result, no references are filtered, they
> all matter in the global reclaim case.

You are right of course. Sorry I am probably still in the vacation
mode...

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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