Re: [PATCH] Page writeback broken after resume: wb_timer lost

[Mark Lord <lkml@rtr.ca>]

Mark Lord wrote:
> Johannes Stezenbach wrote:
> > On Sat, May 20, 2006, Andrew Morton wrote:
> > > From: Andrew Morton <akpm@osdl.org>
> > >
> > > pdflush is carefully designed to ensure that all wakeups have some
> > > corresponding work to do - if a woken-up pdflush thread discovers 
> > > that it
> > > hasn't been given any work to do then this is considered an error.
> > >
> > > That all broke when swsusp came along - because a timer-delivered 
> > > wakeup to a
> > > frozen pdflush thread will just get lost.  This causes the pdflush 
> > > thread to
> > > get lost as well: the writeback timer is supposed to be re-armed by 
> > > pdflush in
> > > process context, but pdflush doesn't execute the callout which does 
> > > this.
> > >
> > > Fix that up by ignoring the return value from try_to_freeze(): jsut 
> > > proceed,
> > > see if we have any work pending and only go back to sleep if that is 
> > > not the
> > > case.
> > >
> > >
> > > Signed-off-by: Andrew Morton <akpm@osdl.org>
> >
> >
> > I've tested this patch for about a week now, by applying it to
> > the 2.6.17-rc3 kernel on my laptop, which I've been using
> > for more than a month now. This patch seems to cure the
> > mysterious symptoms reported in February:
> >
> > http://lkml.org/lkml/2006/2/6/167
> > http://lkml.org/lkml/2006/2/6/170
> > http://lkml.org/lkml/2006/2/13/424
> > etc.
> >
> > Actually I didn't remember to check "Dirty:" in /proc/meminfo,
> > but when I "sync"ed at the end of my workday, just prior to
> > swsupending it, sync returned immediately. with unpatched
> > 2.6.17-rc3, sync would take half a minute
...
> I just gave it a try here.  With or without a suspend/resume cycle after 
> boot,
> the "sync" time is much quicker.  But the Dirty count in /proc/meminfo
> still shows very huge (eg. 600MB) values that never really get smaller
> until I type "sync".  But that subsequent "sync" only takes a couple
> of seconds now, rather than 10-20 seconds like before.
..

Yup, behaviour is *definitely* much better now.  I'm not sure why
the /proc/meminfo "Dirty" count lags behind reality, but the disk
is being kept much more up-to-date than without this patch.

Thanks!
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