Message-ID: <4FE2D73C.3060001@kernel.org>
Date: Thu, 21 Jun 2012 17:11:40 +0900
From: Minchan Kim <minchan@kernel.org>
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Newsgroups: gmane.linux.kernel,gmane.linux.kernel.mm
To: David Rientjes <rientjes@google.com>
CC: Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Rik van Riel <riel@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [patch] mm, thp: abort compaction if migration page cannot be
 charged to memcg
References: <alpine.DEB.2.00.1206202351030.28770@chino.kir.corp.google.com>
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On 06/21/2012 03:52 PM, David Rientjes wrote:

> If page migration cannot charge the new page to the memcg,
> migrate_pages() will return -ENOMEM.  This isn't considered in memory
> compaction however, and the loop continues to iterate over all pageblocks
> trying in a futile attempt to continue migrations which are only bound to
> fail.


Hmm, it might be dumb question.
I imagine that pages in next pageblock could be in another memcg so it could be successful.
Why should we stop compaction once it fails to migrate pages in current pageblock/memcg?

> 
> This will short circuit and fail memory compaction if migrate_pages()
> returns -ENOMEM.  COMPACT_PARTIAL is returned in case some migrations
> were successful so that the page allocator will retry.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  mm/compaction.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -701,8 +701,11 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
>  		if (err) {
>  			putback_lru_pages(&cc->migratepages);
>  			cc->nr_migratepages = 0;
> +			if (err == -ENOMEM) {
> +				ret = COMPACT_PARTIAL;
> +				goto out;
> +			}
>  		}
> -
>  	}
>  
>  out:


-- 
Kind regards,
Minchan Kim
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