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Date: Fri, 11 Jul 2014 11:58:38 -0400
From: Tejun Heo <tj@kernel.org>
Subject: Re: [RFC Patch V1 07/30] mm: Use cpu_to_mem()/numa_mem_id() to
 support memoryless node
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To: Christoph Lameter <cl@gentwo.org>
Cc: Jiang Liu <jiang.liu@linux.intel.com>, Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, David Rientjes <rientjes@google.com>, Mike Galbraith <umgwanakikbuti@gmail.com>, Peter Zijlstra <peterz@infradead.org>, "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>, Vladimir Davydov <vdavydov@parallels.com>, Johannes Weiner <hannes@cmpxchg.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Rik van Riel <riel@redhat.com>, Wanpeng Li <liwanp@linux.vnet.ibm.com>, Zhang Yanfei <zhangyanfei@cn.fujitsu.com>, Catalin Marinas <catalin.marinas@arm.com>, Jianyu Zhan <nasa4836@gmail.com>, malc <av1474@comtv.ru>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Fabian Frederick <fabf@skynet.be>, Tony Luck <tony.luck@intel.com>, linux-mm@kvack.org, linux-hotplug@vger.kernel.org, linux-kernel@vger.kernel.org

On Fri, Jul 11, 2014 at 10:55:59AM -0500, Christoph Lameter wrote:
> > Where X is the memless node.  num_mem_id() on X would return either B
> > or C, right?  If B or C can't satisfy the allocation, the allocator
> > would fallback to A from B and D for C, both of which aren't optimal.
> > It should first fall back to C or B respectively, which the allocator
> > can't do anymoe because the information is lost when the caller side
> > performs numa_mem_id().
> 
> True but the advantage is that the numa_mem_id() allows the use of a
> consitent sort of "local" node which increases allocator performance due
> to the abillity to cache objects from that node.

But the allocator can do the mapping the same.  I really don't see why
we'd push the distinction to the individual users.

Thanks.

-- 
tejun

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