linux-kernel - Re: [PATCH] memcg: make CONFIG_MEMCG depend on CONFIG

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Message-ID: <20150304190635.GC21350@phnom.home.cmpxchg.org>
Date:	Wed, 4 Mar 2015 14:06:35 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Chen Gang <762976180@...com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg: make CONFIG_MEMCG depend on CONFIG_MMU

On Wed, Mar 04, 2015 at 07:07:08PM +0100, Michal Hocko wrote:
> CONFIG_MEMCG might be currently enabled also for !MMU architectures
> which was probably an omission because Balbir had this on the TODO
> list section (https://lkml.org/lkml/2008/3/16/59)
> "
> Only when CONFIG_MMU is enabled, is the virtual address space control
> enabled. Should we do this for nommu cases as well? My suspicion is
> that we don't have to.
> "
> I do not see any traces for !MMU requests after then. The code compiles
> with !MMU but I haven't heard about anybody using it in the real life
> so it is not clear to me whether it works and it is usable at all
> considering how !MMU configuration is restricted.
> 
> Let's make CONFIG_MEMCG depend on CONFIG_MMU to make our support
> explicit and also to get rid of few ifdefs in the code base.
> 
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

Sorry about the misunderstanding, I actually acked Chen's patch.  As I
said, there is nothing inherent in memcg that would prevent using it
on NOMMU systems except for this charges-follow-tasks feature, so I'd
rather fix the compiler warning than adding this dependency.

Thanks
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