Re: [RFC Patch V1 07/30] mm: Use cpu_to_mem()/numa_mem_id() to support memoryless node

From: Christoph Lameter
Date: Fri Jul 11 2014 - 12:19:27 EST

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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