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Date: Mon, 2 Feb 2015 16:03:21 +0900
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Zhang Yanfei <zhangyanfei.ok@hotmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>, Mel Gorman <mgorman@suse.de>,
        David Rientjes <rientjes@google.com>, Rik van Riel <riel@redhat.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/4] mm/page_alloc: separate steal decision from steal
 behaviour part
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On Sat, Jan 31, 2015 at 08:38:10PM +0800, Zhang Yanfei wrote:
> At 2015/1/30 20:34, Joonsoo Kim wrote:
> > From: Joonsoo <iamjoonsoo.kim@lge.com>
> > 
> > This is preparation step to use page allocator's anti fragmentation logic
> > in compaction. This patch just separates steal decision part from actual
> > steal behaviour part so there is no functional change.
> > 
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > ---
> >  mm/page_alloc.c | 49 ++++++++++++++++++++++++++++++++-----------------
> >  1 file changed, 32 insertions(+), 17 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 8d52ab1..ef74750 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1122,6 +1122,24 @@ static void change_pageblock_range(struct page *pageblock_page,
> >  	}
> >  }
> >  
> > +static bool can_steal_freepages(unsigned int order,
> > +				int start_mt, int fallback_mt)
> > +{
> > +	if (is_migrate_cma(fallback_mt))
> > +		return false;
> > +
> > +	if (order >= pageblock_order)
> > +		return true;
> > +
> > +	if (order >= pageblock_order / 2 ||
> > +		start_mt == MIGRATE_RECLAIMABLE ||
> > +		start_mt == MIGRATE_UNMOVABLE ||
> > +		page_group_by_mobility_disabled)
> > +		return true;
> > +
> > +	return false;
> > +}
> 
> So some comments which can tell the cases can or cannot steal freepages
> from other migratetype is necessary IMHO. Actually we can just
> move some comments in try_to_steal_pages to here.

Yes, move some comments looks sufficient to me. I will fix it.

Thanks.