linux-kernel - Re: hugetlb pages not accounted for in rss

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Date:	Tue, 28 Jul 2015 17:53:32 -0700
From:	Jörn Engel <joern@...estorage.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Mike Kravetz <mike.kravetz@...cle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: hugetlb pages not accounted for in rss

On Tue, Jul 28, 2015 at 04:30:19PM -0700, David Rientjes wrote:
> 
> It's not only the oom killer, I don't believe hugeltb pages are accounted 
> to the "rss" in memcg.  They use the hugetlb_cgroup for that.  Starting to 
> account for them in existing memcg deployments would cause them to hit 
> their memory limits much earlier.  The "rss_huge" field in memcg only 
> represents transparent hugepages.
> 
> I agree with your comment that having done this when hugetlbfs was 
> introduced would have been optimal.
> 
> It's always difficult to add a new class of memory to an existing metric 
> ("new" here because it's currently unaccounted).
> 
> If we can add yet another process metric to track hugetlbfs memory mapped, 
> then the test could be converted to use that.  I'm not sure if the 
> jusitifcation would be strong enough, but you could try.

Well, we definitely need something.  Having a 100GB process show 3GB of
rss is not very useful.  How would we notice a memory leak if it only
affects hugepages, for example?

Jörn

--
The object-oriented version of 'Spaghetti code' is, of course, 'Lasagna code'.
(Too many layers).
-- Roberto Waltman.
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