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

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Date:	Thu, 20 Aug 2015 14:36:12 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	David Rientjes <rientjes@...gle.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 2015/8/20 8:02, David Rientjes wrote:
> 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?
Hi David,
	Great idea:) I think that means we are going to kill the
concept of memoryless node, and we only need to specially handle
a few callers who really care about whether there is memory on
local node.
	Then I need some time to audit all usages of __GFP_THISNODE
and update you whether it's doable.
Thanks!
Gerry

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