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

[Johannes Stezenbach <js@linuxtv.org>]

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. Maybe Mark can give
this patch a spin to check if it cures his problem, too.
(I still use vmware, so vmware was not the culprit.)


Thanks,
Johannes


> ---
> 
>  mm/pdflush.c |    9 ++-------
>  1 files changed, 2 insertions(+), 7 deletions(-)
> 
> diff -puN mm/pdflush.c~pdflush-handle-resume-wakeups mm/pdflush.c
> --- devel/mm/pdflush.c~pdflush-handle-resume-wakeups	2006-05-20 17:02:21.000000000 -0700
> +++ devel-akpm/mm/pdflush.c	2006-05-20 17:11:25.000000000 -0700
> @@ -104,13 +104,8 @@ static int __pdflush(struct pdflush_work
>  		list_move(&my_work->list, &pdflush_list);
>  		my_work->when_i_went_to_sleep = jiffies;
>  		spin_unlock_irq(&pdflush_lock);
> -
>  		schedule();
> -		if (try_to_freeze()) {
> -			spin_lock_irq(&pdflush_lock);
> -			continue;
> -		}
> -
> +		try_to_freeze();
>  		spin_lock_irq(&pdflush_lock);
>  		if (!list_empty(&my_work->list)) {
>  			printk("pdflush: bogus wakeup!\n");
> @@ -118,7 +113,7 @@ static int __pdflush(struct pdflush_work
>  			continue;
>  		}
>  		if (my_work->fn == NULL) {
> -			printk("pdflush: NULL work function\n");
> +			printk("pflush: resuming\n");
>  			continue;
>  		}
>  		spin_unlock_irq(&pdflush_lock);
> _
> 
> 
> 
>