linux-kernel - Re: [patch v3 6/6] mm, compaction: terminate async compaction when rescheduling

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Date:	Wed, 07 May 2014 14:10:45 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Greg Thelen <gthelen@...gle.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch v3 6/6] mm, compaction: terminate async compaction when
 rescheduling

On 05/07/2014 04:22 AM, David Rientjes wrote:
> Async compaction terminates prematurely when need_resched(), see
> compact_checklock_irqsave().  This can never trigger, however, if the
> cond_resched() in isolate_migratepages_range() always takes care of the
> scheduling.
>
> If the cond_resched() actually triggers, then terminate this pageblock scan for
> async compaction as well.
>
> Signed-off-by: David Rientjes <rientjes@...gle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>   mm/compaction.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -500,8 +500,13 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
>   			return 0;
>   	}
>
> +	if (cond_resched()) {
> +		/* Async terminates prematurely on need_resched() */
> +		if (cc->mode == MIGRATE_ASYNC)
> +			return 0;
> +	}
> +
>   	/* Time to isolate some pages for migration */
> -	cond_resched();
>   	for (; low_pfn < end_pfn; low_pfn++) {
>   		/* give a chance to irqs before checking need_resched() */
>   		if (locked && !(low_pfn % SWAP_CLUSTER_MAX)) {
>

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