linux-kernel - Re: [PATCH] page_alloc: skip cpuset enforcement for lower zone allocations (v4)

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Message-ID: <20140530214344.GA14720@amt.cnet>
Date:	Fri, 30 May 2014 18:43:45 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Christoph Lameter <cl@...two.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Li Zefan <lizefan@...wei.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Lai Jiangshan <laijs@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Tejun Heo <tj@...nel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] page_alloc: skip cpuset enforcement for lower zone
 allocations (v4)

On Fri, May 30, 2014 at 08:48:41AM -0500, Christoph Lameter wrote:
> On Thu, 29 May 2014, Andrew Morton wrote:
> 
> > >
> > > 	if (!nodemask && gfp_zone(gfp_mask) < policy_zone)
> > > 		nodemask = &node_states[N_ONLINE];
> >
> > OK, thanks, I made the patch go away for now.
> >
> 
> And another issue is that the policy_zone may be highmem on 32 bit
> platforms which will result in ZONE_NORMAL to be exempted.
> 
> policy zone can actually even be ZONE_DMA for some platforms. The
> check would not be useful at all on those.
> 
> Ignoring the containing cpuset only makes sense for GFP_DMA32 on
> 64 bit platforms and for GFP_DMA on platforms where there is an actual
> difference in the address spaces supported by GFP_DMA (such as x86).
> 
> Generally I think this is only useful for platforms that attempt to
> support legacy devices only able to DMA to a portion of the memory address
> space and that at the same time support NUMA for large address spaces.
> This is a contradiction on the one hand this is a high end system and on
> the other hand it attempts to support crippled DMA devices?

OK we will handle this in userspace.

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