Re: [PATCH] mm/page_alloc: Wait for oom_lock before retrying.

[Michal Hocko <mhocko@suse.com>]

On Thu 15-12-16 01:36:07, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Wed 14-12-16 20:37:07, Tetsuo Handa wrote:
> > > Michal Hocko wrote:
[...]
> > > > So it would be really great if you could
> > > > 	1) test with the fixed throttling
> > > > 	2) loglevel=4 on the kernel command line
> > > > 	3) try the above with the same loglevel
> > > > 
> > > > ideally 1) would be sufficient and that would make the most sense from
> > > > the warn_alloc point of view. If this is 2 or 3 then we are hitting a
> > > > more generic problem and I would be quite careful to hack it around.
> > > 
> > > Thus, I don't think I can do these.
> > 
> > i think this would be really valuable.
> 
> OK. I tried 1) and 2). I didn't try 3) because printk() did not work as expected.
> 
> Regarding 1), it did not help. I can still see "** XXX printk messages dropped **"
> ( http://I-love.SAKURA.ne.jp/tmp/serial-20161215-1.txt.xz ).

So we still manage to swamp the logbuffer. The question is whether you
can still see the lockup. This is not obvious from the output to me.

> Regarding 2), I can't tell whether it helped
> ( http://I-love.SAKURA.ne.jp/tmp/serial-20161215-2.txt.xz ).
> I can no longer see "** XXX printk messages dropped **", but sometimes they stalled.
> In most cases, "Out of memory: " and "Killed process" lines are printed within 0.1
> second. But sometimes it took a few seconds. Less often it took longer than a minute.
> There was one big stall which lasted for minutes. I changed loglevel to 7 and checked
> memory information. Seems that watermark was low enough to call out_of_memory().

Isn't that what your test case essentially does though? Keep the system
in OOM continually? Some stalls are to be expected I guess, the main
question is whether there is a point with no progress at all.
-- 
Michal Hocko
SUSE Labs

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