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SubjectRe: [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@chello.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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