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From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [patch v3 3/6] mm, compaction: add per-zone migration pfn cache for async compaction
Date: Wed,  7 May 2014 16:56:21 -0400
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To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>, Vlastimil Babka <vbabka@suse.cz>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Greg Thelen <gthelen@google.com>, Hugh Dickins <hughd@google.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org

On Tue, May 06, 2014 at 07:22:45PM -0700, David Rientjes wrote:
> Each zone has a cached migration scanner pfn for memory compaction so that 
> subsequent calls to memory compaction can start where the previous call left 
> off.
> 
> Currently, the compaction migration scanner only updates the per-zone cached pfn 
> when pageblocks were not skipped for async compaction.  This creates a 
> dependency on calling sync compaction to avoid having subsequent calls to async 
> compaction from scanning an enormous amount of non-MOVABLE pageblocks each time 
> it is called.  On large machines, this could be potentially very expensive.
> 
> This patch adds a per-zone cached migration scanner pfn only for async 
> compaction.  It is updated everytime a pageblock has been scanned in its 
> entirety and when no pages from it were successfully isolated.  The cached 
> migration scanner pfn for sync compaction is updated only when called for sync 
> compaction.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  v3: do not update pageblock skip metadata when skipped due to async per
>      Vlastimil.

Looks good to me.
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

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