On 07/30/2015 07:41 PM, Johannes Weiner wrote:
On Thu, Jul 30, 2015 at 06:34:31PM +0200, Vlastimil Babka wrote:numa_mem_id() is able to handle allocation from CPUs on memory-less nodes, so it's a more robust fallback than the currently used numa_node_id().Won't it fall through to the next closest memory node in the zonelist anyway?
Right, I would expect the zonelist of memoryless node to be the same as of the closest node. Documentation/vm/numa seems to agree.
Is this for callers doing NUMA_NO_NODE with __GFP_THISZONE?I guess that's the only scenario where that matters, yeah. And there might well be no such caller now, but maybe some will sneak in without the author testing on a system with memoryless node.
Note that with !CONFIG_HAVE_MEMORYLESS_NODES, numa_mem_id() just does numa_node_id().
So yeah I think "a more robust fallback" is correct :) But let's put it explicitly in changelog then:
----8<----alloc_pages_node() might fail when called with NUMA_NO_NODE and __GFP_THISNODE on a CPU belonging to a memoryless node. To make the local-node fallback more robust and prevent such situations, use numa_mem_id(), which was introduced for similar scenarios in the slab context.
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