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Date: Thu, 1 May 2014 14:02:00 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
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To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
cc: Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>, vbabka@suse.cz, iamjoonsoo.kim@lge.com,
        gthelen@google.com, Hugh Dickins <hughd@google.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch 2/2] mm, compaction: return failed migration target pages
 back to freelist
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On Thu, 1 May 2014, Naoya Horiguchi wrote:

> > diff --git a/mm/compaction.c b/mm/compaction.c
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -797,6 +797,19 @@ static struct page *compaction_alloc(struct page *migratepage,
> >  }
> >  
> >  /*
> > + * This is a migrate-callback that "frees" freepages back to the isolated
> > + * freelist.  All pages on the freelist are from the same zone, so there is no
> > + * special handling needed for NUMA.
> > + */
> > +static void compaction_free(struct page *page, unsigned long data)
> > +{
> > +	struct compact_control *cc = (struct compact_control *)data;
> > +
> > +	list_add(&page->lru, &cc->freepages);
> > +	cc->nr_freepages++;
> 
> With this change, migration_page() handles cc->nr_freepages consistently, so
> we don't have to run over freelist to update this count in update_nr_listpages()?
> 

Good optimization, I'll add it!