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

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Date:	Wed, 29 Feb 2012 03:02:46 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Michal Hocko <mhocko@...e.cz>, 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, Feb 29, 2012 at 09:39:46AM +0900, KAMEZAWA Hiroyuki wrote:
> On Tue, 28 Feb 2012 15:14:49 +0100
> Johannes Weiner <hannes@...xchg.org> wrote:
> > --- 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);
> 
> 
> I'm sorry if I don't understand the codes... !sc->target_mem_cgroup case is handled ?

Yes, but it's not obvious from the diff alone.  page_referenced() does
this:

		/*
		 * If we are reclaiming on behalf of a cgroup, skip
		 * counting on behalf of references from different
		 * cgroups
		 */
		if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
			continue;

As a result, !sc->target_mem_cgroup -- global reclaim -- will never
ignore references, or put differently, respect references from all
memcgs, which is what we want.
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