linux-kernel - Re: [PATCH 2/5] vmscan: sleep only if backingdev is congested

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Date:	Sat, 25 Aug 2012 19:02:49 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] vmscan: sleep only if backingdev is congested

On 08/22/2012 03:15 AM, Minchan Kim wrote:

> +++ b/mm/vmscan.c
> @@ -2705,8 +2705,16 @@ loop_again:
>   		if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
>   			if (has_under_min_watermark_zone)
>   				count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
> -			else
> -				congestion_wait(BLK_RW_ASYNC, HZ/10);
> +			else {
> +				for (i = 0; i <= end_zone; i++) {
> +					struct zone *zone = pgdat->node_zones
> +								+ i;
> +					if (!populated_zone(zone))
> +						continue;
> +					wait_iff_congested(zone, BLK_RW_ASYNC,
> +								HZ/10);
> +				}
> +			}
>   		}

Do we really want to wait on every zone?

That could increase the sleep time by a factor 3.

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