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SubjectRe: [PATCH] Page writeback broken after resume: wb_timer lost
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);
> _
>
>
>
>
-
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