linux-kernel - Re: [Patch V3 3/9] sgi-xp: Replace cpu_to_node() with cpu_to

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Date:	Wed, 19 Aug 2015 17:02:54 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Tang Chen <tangchen@...fujitsu.com>, Tejun Heo <tj@...nel.org>,
	Cliff Whickman <cpw@....com>,
	Robin Holt <robinmholt@...il.com>,
	Tony Luck <tony.luck@...el.com>, linux-mm@...ck.org,
	linux-hotplug@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [Patch V3 3/9] sgi-xp: Replace cpu_to_node() with cpu_to_mem()
 to support memoryless node

On Wed, 19 Aug 2015, Jiang Liu wrote:

> > Why not simply fix build_zonelists_node() so that the __GFP_THISNODE 
> > zonelists are set up to reference the zones of cpu_to_mem() for memoryless 
> > nodes?
> > 
> > It seems much better than checking and maintaining every __GFP_THISNODE 
> > user to determine if they are using a memoryless node or not.  I don't 
> > feel that this solution is maintainable in the longterm.
> Hi David,
> 	There are some usage cases, such as memory migration,
> expect the page allocator rejecting memory allocation requests
> if there is no memory on local node. So we have:
> 1) alloc_pages_node(cpu_to_node(), __GFP_THISNODE) to only allocate
> memory from local node.
> 2) alloc_pages_node(cpu_to_mem(), __GFP_THISNODE) to allocate memory
> from local node or from nearest node if local node is memoryless.
> 

Right, so do you think it would be better to make the default zonelists be 
setup so that cpu_to_node()->zonelists == cpu_to_mem()->zonelists and then 
individual callers that want to fail for memoryless nodes check 
populated_zone() themselves?
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