linux-kernel - Re: [PATCH 11/11] protect architectures where THREAD_SIZE >= PAGE

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Date:	Tue, 26 Jun 2012 02:05:47 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Glauber Costa <glommer@...allels.com>
cc:	cgroups@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Pekka Enberg <penberg@...nel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>, devel@...nvz.org,
	kamezawa.hiroyu@...fujitsu.com, Tejun Heo <tj@...nel.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Frederic Weisbecker <fweisbec@...hat.com>
Subject: Re: [PATCH 11/11] protect architectures where THREAD_SIZE >= PAGE_SIZE
 against fork bombs

On Tue, 26 Jun 2012, Glauber Costa wrote:

> > Right, because I'm sure that __GFP_KMEMCG will be used in additional
> > places outside of this patchset and it will be a shame if we have to
> > always add #ifdef's.  I see no reason why we would care if __GFP_KMEMCG
> > was used when CONFIG_CGROUP_MEM_RES_CTLR_KMEM=n with the semantics that it
> > as in this patchset.  It's much cleaner by making it 0x0 when disabled.
> > 
> 
> What I can do, instead, is to WARN_ON conditionally to the config option in
> the page allocator, and make sure no one is actually passing the flag in that
> case.
> 

I don't think adding a conditional to the page allocator's fastpath when 
CONFIG_CGROUP_MEM_RES_CTLR_KMEM=n is appropriate.  I don't understand why 
this can't be 0x0 for such a configuration, __GFP_KMEM certainly means 
nothing when we don't have it enabled so how is this different at all from 
kmemcheck?
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