linux-kernel - Re: [PATCH 11/11] Do not compact within a preferred zone after a compaction failure

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Date:	Tue, 23 Mar 2010 13:31:43 -0500 (CDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 11/11] Do not compact within a preferred zone after a
 compaction failure

On Tue, 23 Mar 2010, Mel Gorman wrote:

> The fragmentation index may indicate that a failure it due to external

s/it/is/

> fragmentation, a compaction run complete and an allocation failure still

???

> fail. There are two obvious reasons as to why
>
>   o Page migration cannot move all pages so fragmentation remains
>   o A suitable page may exist but watermarks are not met
>
> In the event of compaction and allocation failure, this patch prevents
> compaction happening for a short interval. It's only recorded on the

compaction is "recorded"? deferred?

> preferred zone but that should be enough coverage. This could have been
> implemented similar to the zonelist_cache but the increased size of the
> zonelist did not appear to be justified.

> @@ -1787,6 +1787,9 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
>  			 */
>  			count_vm_event(COMPACTFAIL);
>
> +			/* On failure, avoid compaction for a short time. */
> +			defer_compaction(preferred_zone, jiffies + HZ/50);
> +

20ms? How was that interval determined?

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