linux-kernel - Re: [patch 08/12] mm: page_alloc: wait for OOM killer progress before retrying

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Message-ID: <20150326182352.GB16898@phnom.home.cmpxchg.org>
Date:	Thu, 26 Mar 2015 14:23:52 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Huang Ying <ying.huang@...el.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	Theodore Ts'o <tytso@....edu>
Subject: Re: [patch 08/12] mm: page_alloc: wait for OOM killer progress
 before retrying

On Thu, Mar 26, 2015 at 04:58:46PM +0100, Michal Hocko wrote:
> On Wed 25-03-15 02:17:12, Johannes Weiner wrote:
> > There is not much point in rushing back to the freelists and burning
> > CPU cycles in direct reclaim when somebody else is in the process of
> > OOM killing, or right after issuing a kill ourselves, because it could
> > take some time for the OOM victim to release memory.
> 
> Yes this makes sense and it is better than what we have now. The
> question is how long we should wait. I can see you have gone with HZ.
> What is the value based on? Have your testing shown that the OOM victim
> manages to die within a second most of the time?
> 
> I do not want to get into which value is the best discussion but I would
> expect a larger value. Most OOM victims are not blocked so they would
> wake up soon. This is a safety net for those who are blocked and I do
> not think we have to expedite those rare cases and rather optimize for
> "regular" OOM situations. How about 10-30s?

Yup, I agree with that reasoning.  We can certainly go higher than HZ.

However, we should probably try to stay within the thresholds of any
lock/hang detection watchdogs, which on a higher level includes the
user itself, who might get confused if the machine hangs for 30s.

As I replied to Vlastimil, once the OOM victim hangs for several
seconds without a deadlock, failing the allocation wouldn't seem
entirely unreasonable, either.

But yes, something like 5-10s would still sound good to me.
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