linux-kernel - Re: [PATCH] mm: memcontrol: Let mem_cgroup_move_account() have effect only if MMU enabled

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Message-ID: <20150304174056.GA20376@phnom.home.cmpxchg.org>
Date:	Wed, 4 Mar 2015 12:40:56 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Chen Gang <762976180@...com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: memcontrol: Let mem_cgroup_move_account() have
 effect only if MMU enabled

On Tue, Mar 03, 2015 at 02:45:24PM +0100, Michal Hocko wrote:
> On Tue 03-03-15 06:42:01, Chen Gang wrote:
> > When !MMU, it will report warning. The related warning with allmodconfig
> > under c6x:
> 
> Does it even make any sense to enable CONFIG_MEMCG when !CONFIG_MMU?
> Is anybody using this configuration and is it actually usable? My
> knowledge about CONFIG_MMU is close to zero so I might be missing
> something but I do not see a point into fixing compile warnings when
> the whole subsystem is not usable in the first place.

It's very limited, and anonymous memory is not even charged right now,
even though it could be -- see nommu.c::do_mmap_private().  But there
is nothing inherent in the memcg functionality that would require an
MMU I guess, except for these ridiculous charge moving pte walkers.

> > Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>
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