Re: [PATCH v2 3/7] x86, gfp: Cache best near node for memory allocation.

From: Tang Chen
Date: Sun Sep 27 2015 - 21:52:09 EST

Hi, tj,

On 09/27/2015 01:53 AM, Tejun Heo wrote:
Hello, Tang.

On Sat, Sep 26, 2015 at 05:31:07PM +0800, Tang Chen wrote:
@@ -307,13 +307,19 @@ static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask,
if (nid < 0)
nid = numa_node_id();
+ if (!node_online(nid))
+ nid = get_near_online_node(nid);
return __alloc_pages(gfp_mask, order, node_zonelist(nid, gfp_mask));
Why not just update node_data[]->node_zonelist in the first place?
zonelist will be rebuilt in __offline_pages() when the zone is not populated
any more.

Here, getting the best near online node is for those cpus on memory-less

In the original code, if nid is NUMA_NO_NODE, the node the current cpu
resides in
will be chosen. And if the node is memory-less node, the cpu will be mapped
to its
best near online node.

But this patch-set will map the cpu to its original node, so numa_node_id()
may return
a memory-less node to allocator. And then memory allocation may fail.
Correct me if I'm wrong but the zonelist dictates which memory areas
the page allocator is gonna try to from, right? What I'm wondering is
why we aren't handling memory-less nodes by simply updating their
zonelists. I mean, if, say, node 2 is memory-less, its zonelist can
simply point to zones from other nodes, right? What am I missing

Oh, yes, you are right. But I remember some time ago, Liu, Jiang has or was
going to handle memory less node like this in his patch:

BTW, to Liu Jiang, how is your patches going on ?



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