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!