linux-kernel - Re: [PATCH 18/45] writeback: introduce wait queue for balance_dirty

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Message-Id: <20091008171114.d2763f9d.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 8 Oct 2009 17:11:14 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	Myklebust Trond <Trond.Myklebust@...app.com>,
	"jens.axboe@...cle.com" <jens.axboe@...cle.com>,
	Jan Kara <jack@...e.cz>, Nick Piggin <npiggin@...e.de>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/45] writeback: introduce wait queue for
 balance_dirty_pages()

On Thu, 08 Oct 2009 10:08:36 +0200
Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Thu, 2009-10-08 at 09:58 +0800, Wu Fengguang wrote:
> > 
> > > How this runqueue->nr_iowait is handled now ?
> > 
> > Good question. io_schedule() has an old comment for throttling IO wait:
> > 
> >          * But don't do that if it is a deliberate, throttling IO wait (this task
> >          * has set its backing_dev_info: the queue against which it should throttle)
> >          */
> >         void __sched io_schedule(void)
> > 
> > So it looks both Jens' and this patch behaves right in ignoring the
> > iowait accounting for balance_dirty_pages() :)
> 
> Well it is a change in behaviour, and I think IOWAIT makes sense when
> we're blocked due to io throttle..
> 
> Hmm?
> 
Above comment "don't do that if it is a deliberate, throttling IO wait" is
really old but ignored.
I pesonally don't like to change the meanig of iowait in /proc/stat. 
But I'm not sure which is better to change the definitiion (which was ignored) or
fix behavior (not correct very long time)...

Hmm?, too ;)

Regards,
-Kame

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