From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Lameter <cl@gentwo.org>
Date: Fri, 11 Jul 2014 16:19:14 +0000
Subject: Re: [RFC Patch V1 07/30] mm: Use cpu_to_mem()/numa_mem_id() to support memoryless node
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To: Tejun Heo <tj@kernel.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, 11 Jul 2014, Tejun Heo wrote:

> On Fri, Jul 11, 2014 at 10:58:52AM -0500, Christoph Lameter wrote:
> > > But, GFP_THISNODE + numa_mem_id() is identical to numa_node_id() +
> > > nearest node with memory fallback.  Is there any case where the user
> > > would actually want to always fail if it's on the memless node?
> >
> > GFP_THISNODE allocatios must fail if there is no memory available on
> > the node. No fallback allowed.
>
> I don't know.  The intention is that the caller wants something on
> this node or the caller will fail or fallback ourselves, right?  For
> most use cases just considering the nearest memory node as "local" for
> memless nodes should work and serve the intentions of the users close
> enough.  Whether that'd be better or we'd be better off with something
> else depends on the details for sure.

Yes that works. But if we want a consistent node to allocate from (and
avoid the fallbacks) then we need this patch. I think this is up to those
needing memoryless nodes to figure out what semantics they need.