linux-kernel - Re: kswapd0: excessive CPU usage

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Message-ID: <5096999F.1040405@redhat.com>
Date:	Sun, 04 Nov 2012 11:36:47 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Thorsten Leemhuis <fedora@...mhuis.info>,
	Jiri Slaby <jslaby@...e.cz>, Valdis.Kletnieks@...edu,
	Jiri Slaby <jirislaby@...il.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: kswapd0: excessive CPU usage

On 10/30/2012 03:18 PM, Mel Gorman wrote:

>   restart:
> -	wake_all_kswapd(order, zonelist, high_zoneidx,
> +	/*
> +	 * kswapd is woken except when this is a THP request and compaction
> +	 * is deferred. If we are backing off reclaim/compaction then kswapd
> +	 * should not be awake aggressively reclaiming with no consumers of
> +	 * the freed pages
> +	 */
> +	if (!(is_thp_alloc(gfp_mask, order) &&
> +	      compaction_deferred(preferred_zone, order)))
> +		wake_all_kswapd(order, zonelist, high_zoneidx,
>   					zone_idx(preferred_zone));

What is special about thp allocations here?

Surely other large allocations that keep failing
should get the same treatment, of not waking up
kswapd if compaction is deferred?

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