linux-kernel - Re: mm: pages are not freed from lru_add

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Message-ID: <20160511073814.GD16677@dhcp22.suse.cz>
Date:	Wed, 11 May 2016 09:38:14 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	"Odzioba, Lukasz" <lukasz.odzioba@...el.com>
Cc:	"Hansen, Dave" <dave.hansen@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Shutemov, Kirill" <kirill.shutemov@...el.com>,
	"Anaczkowski, Lukasz" <lukasz.anaczkowski@...el.com>
Subject: Re: mm: pages are not freed from lru_add_pvecs after process
 termination

On Thu 05-05-16 17:25:07, Odzioba, Lukasz wrote:
> On Thu 05-05-16 09:21:00, Michal Hocko wrote: 
> > OK, it wasn't that tricky afterall. Maybe I have missed something but
> > the following should work. Or maybe the async nature of flushing turns
> > out to be just impractical and unreliable and we will end up skipping
> > THP (or all compound pages) for pcp LRU add cache. Let's see...
> 
> Initially this issue was found on RH's 3.10.x kernel, but now I am using 
> 4.6-rc6.
> 
> In overall it does help and under heavy load it is slightly better than the
> second patch. Unfortunately I am still able to hit 10-20% oom kills with it -
> (went down from 30-50%) partially due to earlier vmstat_update call
>  - it went up to 25-25% with this patch below:

This simply shows that this is not a viable option. So I guess we really
want to rather skip THP (compound pages) from LRU add pcp cache. Thanks
for your effort and testing!
-- 
Michal Hocko
SUSE Labs