linux-kernel - Re: [RFC Patch V1 07/30] mm: Use cpu_to_mem()/numa_mem

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Message-ID: <alpine.DEB.2.11.1407111117560.27592@gentwo.org>
Date:	Fri, 11 Jul 2014 11:19:14 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Tejun Heo <tj@...nel.org>
cc:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Jianyu Zhan <nasa4836@...il.com>, malc <av1474@...tv.ru>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Fabian Frederick <fabf@...net.be>,
	Tony Luck <tony.luck@...el.com>, linux-mm@...ck.org,
	linux-hotplug@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC Patch V1 07/30] mm: Use cpu_to_mem()/numa_mem_id() to
 support memoryless node

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.


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