linux-kernel - Re: [PATCH 8/8] vmscan: Kick flusher threads to clean pages when reclaim is encountering dirty pages

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Date:	Wed, 21 Jul 2010 00:05:51 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 8/8] vmscan: Kick flusher threads to clean pages when
 reclaim is encountering dirty pages

On Tue, Jul 20, 2010 at 03:10:49PM +0100, Mel Gorman wrote:
> On Tue, Jul 20, 2010 at 12:48:39AM +0200, Johannes Weiner wrote:
> > On Mon, Jul 19, 2010 at 03:37:37PM +0100, Mel Gorman wrote:
> > > although the latter can get disabled too. Deleting the magic is an
> > > option which would trade IO efficiency for power efficiency but my
> > > current thinking is laptop mode preferred reduced power.
> > 
> > Maybe couple your wakeup with sc->may_writepage?  It is usually false
> > for laptop_mode but direct reclaimers enable it at one point in
> > do_try_to_free_pages() when it scanned more than 150% of the reclaim
> > target, so you could use existing disk spin-up points instead of
> > introducing new ones or disabling the heuristics in laptop mode.
> > 
> 
> How about the following?
> 
>         if (nr_dirty && sc->may_writepage)
>                 wakeup_flusher_threads(laptop_mode ? 0 :
>                                                 nr_dirty + nr_dirty / 2);
> 
> 
> 1. Wakup flusher threads if dirty pages are encountered
> 2. For direct reclaim, only wake them up if may_writepage is set
>    indicating that the system is ready to spin up disks and start
>    reclaiming
> 3. In laptop_mode, flush everything to reduce future spin-ups

Sounds like the sanest approach to me.  Thanks.

	Hannes
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