From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: [PATCH 8/8] vmscan: Kick flusher threads to clean pages when
 reclaim is encountering dirty pages
Date: Tue, 27 Jul 2010 22:55:25 +0800
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Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>
To: Mel Gorman <mel@csn.ul.ie>
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On Tue, Jul 27, 2010 at 10:40:26PM +0800, Mel Gorman wrote:
> 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).

I see your worry about much bigger page size making

        vmscan batch size > writeback batch size

and it's a legitimate worry.

Thanks,
Fengguang