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

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Date:	Tue, 27 Jul 2010 15:40:26 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.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>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Hellwig <hch@...radead.org>,
	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 27, 2010 at 10:34:23PM +0800, Wu Fengguang wrote:
> > If you plan to keep wakeup_flusher_threads(), a simpler form may be
> > sufficient, eg.
> > 
> >         laptop_mode ? 0 : (nr_dirty * 16)
> 
> This number is not sensitive because the writeback code may well round
> it up to some more IO efficient value (currently 4MB). AFAIK the
> nr_pages parameters passed by all existing flusher callers are some
> rule-of-thumb value, and far from being an exact number.
> 

I get that it's a rule of thumb but decided I would still pass in some value
related to nr_dirty that was bounded in some manner.  Currently, that bound
is 4MB but maybe it should have been bound to MAX_WRITEBACK_PAGES (which is
4MB for x86, but could be anything depending on the base page size).

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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