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

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Date:	Fri, 11 Mar 2016 16:28:51 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	hannes@...xchg.org, mgorman@...e.de, rientjes@...gle.com,
	hillf.zj@...baba-inc.com, kamezawa.hiroyu@...fujitsu.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] OOM detection rework v4

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.

-- 
Michal Hocko
SUSE Labs