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

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Message-ID: <alpine.DEB.2.10.1405300841390.8240@gentwo.org>
Date:	Fri, 30 May 2014 08:48:41 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	David Rientjes <rientjes@...gle.com>,
	Marcelo Tosatti <mtosatti@...hat.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 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?

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