linux-kernel - Re: [Alsa-user] new source of MIDI playback slow-down identified - 5a03b051ed87e72b959f32a86054e1142ac4cf55 thp: use compaction in kswapd for GFP

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Date:	Tue, 22 Feb 2011 20:43:25 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Arthur Marsh <arthur.marsh@...ernode.on.net>
Cc:	Clemens Ladisch <cladisch@...glemail.com>,
	alsa-user@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [Alsa-user] new source of MIDI playback slow-down identified -
 5a03b051ed87e72b959f32a86054e1142ac4cf55 thp: use compaction in kswapd for
 GFP_ATOMIC order > 0

On Wed, Feb 23, 2011 at 04:17:44AM +1030, Arthur Marsh wrote:
> OK, these patches applied together against upstream didn't cause a crash 
> but I did observe:
> 
> significant slowdowns of MIDI playback (moreso than in previous cases, 
> and with less than 20 Meg of swap file in use);
> 
> kswapd0 sharing equal top place in CPU usage at times (e.g. 20 percent).
> 
> If I should try only one of the patches or something else entirely, 
> please let me know.

For Mel: with z1, kswapd used only 0.1-3.9 percent of CPU while he
loaded other applications.

We may need a way to put kswapd in all uncompactable mode to solve
this, logic 3 just trying not to disable the all unreclaimable logic
seems not enough. I.e. if compact_zone_order doesn't return
COMPACT_COMPLETE, stop the compaction loop in kswapd. Then we can put
back in the COMPACT_MODE_KSWAPD return COMPACT_CONTINUE in
compact_finished as the caller will throttle it (and it won't run more
than one scan before putting kswapd to sleep in all uncompactable mode).
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