Re: [PATCH 0/3] OOM detection rework v4

[Tetsuo Handa]

Michal Hocko wrote:
> On Fri 11-03-16 22:32:02, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Fri 11-03-16 19:45:29, Tetsuo Handa wrote:
> > > > (Posting as a reply to this thread.)
> > > 
> > > I really do not see how this is related to this thread.
> > 
> > All allocating tasks are looping at
> > 
> >                         /*
> >                          * If we didn't make any progress and have a lot of
> >                          * dirty + writeback pages then we should wait for
> >                          * an IO to complete to slow down the reclaim and
> >                          * prevent from pre mature OOM
> >                          */
> >                         if (!did_some_progress && 2*(writeback + dirty) > reclaimable) {
> >                                 congestion_wait(BLK_RW_ASYNC, HZ/10);
> >                                 return true;
> >                         }
> > 
> > in should_reclaim_retry().
> > 
> > should_reclaim_retry() was added by OOM detection rework, wan't it?
> 
> What happens without this patch applied. In other words, it all smells
> like the IO got stuck somewhere and the direct reclaim cannot perform it
> so we have to wait for the flushers to make a progress for us. Are those
> stuck? Is the IO making any progress at all or it is just too slow and
> it would finish actually.  Wouldn't we just wait somewhere else in the
> direct reclaim path instead.

As of next-20160311, CPU usage becomes 0% when this problem occurs.

If I remove

  mm-use-watermak-checks-for-__gfp_repeat-high-order-allocations-checkpatch-fixes
  mm: use watermark checks for __GFP_REPEAT high order allocations
  mm: throttle on IO only when there are too many dirty and writeback pages
  mm-oom-rework-oom-detection-checkpatch-fixes
  mm, oom: rework oom detection

then CPU usage becomes 60% and most of allocating tasks
are looping at

        /*
         * Acquire the oom lock.  If that fails, somebody else is
         * making progress for us.
         */
        if (!mutex_trylock(&oom_lock)) {
                *did_some_progress = 1;
                schedule_timeout_uninterruptible(1);
                return NULL;
        }

in __alloc_pages_may_oom() (i.e. OOM-livelock due to the OOM reaper disabled).