On Sat 28-11-15 13:39:11, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > for write while write but the probability is reduced considerably wrt.
>
> Is this "while write" garbage?
Fixed
> > Users of mmap_sem which need it for write should be carefully reviewed
> > to use _killable waiting as much as possible and reduce allocations
> > requests done with the lock held to absolute minimum to reduce the risk
> > even further.
>
> It will be nice if we can have down_write_killable()/down_read_killable().
Yes that is an idea.
> > The API between oom killer and oom reaper is quite trivial. wake_oom_reaper
> > updates mm_to_reap with cmpxchg to guarantee only NUll->mm transition
>
> NULL->mm
fixed
> > and oom_reaper clear this atomically once it is done with the work.
>
> Can't oom_reaper() become as compact as below?
Good idea! I think we still need {READ,WRITE}_ONCE to prevent from any
potential mis optimizations, though.
Here is what I did:
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 333953bf4968..b50ce41194b3 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -477,21 +477,11 @@ static void oom_reap_vmas(struct mm_struct *mm)
static int oom_reaper(void *unused)
{
- DEFINE_WAIT(wait);
-
while (true) {
struct mm_struct *mm;
-
- prepare_to_wait(&oom_reaper_wait, &wait, TASK_UNINTERRUPTIBLE);
- mm = READ_ONCE(mm_to_reap);
- if (!mm) {
- freezable_schedule();
- finish_wait(&oom_reaper_wait, &wait);
- } else {
- finish_wait(&oom_reaper_wait, &wait);
- oom_reap_vmas(mm);
- WRITE_ONCE(mm_to_reap, NULL);
- }
+ wait_event_freezable(oom_reaper_wait, (mm = READ_ONCE(mm_to_reap)));
+ oom_reap_vmas(mm);
+ WRITE_ONCE(mm_to_reap, NULL);
}
return 0;
--
Michal Hocko
SUSE Labs
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