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Subject: Re: [PATCH 18/45] writeback: introduce wait queue for
 balance_dirty_pages()
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
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Date: Thu, 08 Oct 2009 10:08:36 +0200
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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?