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Subject: Re: [Patch V3 3/9] sgi-xp: Replace cpu_to_node() with cpu_to_mem() to
 support memoryless node
References: <1439781546-7217-1-git-send-email-jiang.liu@linux.intel.com>
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From: Jiang Liu <jiang.liu@linux.intel.com>
Message-ID: <55D5755C.5060803@linux.intel.com>
Date: Thu, 20 Aug 2015 14:36:12 +0800
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To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, Mike Galbraith <umgwanakikbuti@gmail.com>, Peter Zijlstra <peterz@infradead.org>, "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>, Tang Chen <tangchen@cn.fujitsu.com>, Tejun Heo <tj@kernel.org>, Cliff Whickman <cpw@sgi.com>, Robin Holt <robinmholt@gmail.com>, Tony Luck <tony.luck@intel.com>, linux-mm@kvack.org, linux-hotplug@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org

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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