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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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