linux-kernel - Re: [patch] mm: memcontrol: lockless page counters

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Message-ID: <20140922172800.GA4343@dhcp22.suse.cz>
Date:	Mon, 22 Sep 2014 19:28:00 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	linux-mm@...ck.org, Greg Thelen <gthelen@...gle.com>,
	Dave Hansen <dave@...1.net>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] mm: memcontrol: lockless page counters

On Mon 22-09-14 11:50:49, Johannes Weiner wrote:
> On Mon, Sep 22, 2014 at 04:44:36PM +0200, Michal Hocko wrote:
> > On Fri 19-09-14 09:22:08, Johannes Weiner wrote:
[...]
> > Nevertheless I think that the counter should live outside of memcg (it
> > is ugly and bad in general to make HUGETLB controller depend on MEMCG
> > just to have a counter). If you made kernel/page_counter.c and led both
> > containers select CONFIG_PAGE_COUNTER then you do not need a dependency
> > on MEMCG and I would find it cleaner in general.
> 
> The reason I did it this way is because the hugetlb controller simply
> accounts and limits a certain type of memory and in the future I would
> like to make it a memcg extension, just like kmem and swap.

I am not sure this is the right way to go. Hugetlb has always been
"special" and I do not see any advantage to pull its specialness into
memcg proper. It would just make the code more complicated. I can also
imagine users who simply do not want to pay memcg overhead and use only
hugetlb controller.

Besides that it is not like a separate page_counter with a clear
interface would cause more maintenance overhead so I really do not see
any reason to pull it into memcg.
-- 
Michal Hocko
SUSE Labs
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