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Date: Fri, 24 Jan 2014 15:49:33 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Subject: Re: [PATCH] slub: Don't throw away partial remote slabs if there is
 no local memory
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Cc: Han Pingtian <hanpt@linux.vnet.ibm.com>, penberg@kernel.org,
 linux-mm@kvack.org, paulus@samba.org, Anton Blanchard <anton@samba.org>,
 mpm@selenic.com, Christoph Lameter <cl@linux.com>,
 linuxppc-dev@lists.ozlabs.org, Joonsoo Kim <iamjoonsoo.kim@lge.com>,
 Wanpeng Li <liwanp@linux.vnet.ibm.com>
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On Fri, 24 Jan 2014, Nishanth Aravamudan wrote:

> > I think the problem is a memoryless node being used for kmalloc_node() so 
> > we need to decide where to enforce node_present_pages().  __slab_alloc() 
> > seems like the best candidate when !node_match().
> 
> Actually, this is effectively what Anton's patch does, except with
> Wanpeng's adjustment to use node_present_pages(). Does that seem
> sufficient to you?
> 

I don't see that as being the effect of Anton's patch.  We need to use 
numa_mem_id() as Christoph mentioned when a memoryless node is passed for 
the best NUMA locality.  Something like this:

diff --git a/mm/slub.c b/mm/slub.c
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2278,10 +2278,14 @@ redo:
 
 	if (unlikely(!node_match(page, node))) {
 		stat(s, ALLOC_NODE_MISMATCH);
-		deactivate_slab(s, page, c->freelist);
-		c->page = NULL;
-		c->freelist = NULL;
-		goto new_slab;
+		if (unlikely(!node_present_pages(node)))
+			node = numa_mem_id();
+		if (!node_match(page, node)) {
+			deactivate_slab(s, page, c->freelist);
+			c->page = NULL;
+			c->freelist = NULL;
+			goto new_slab;
+		}
 	}
 
 	/*

> It does only cover the memoryless node case (not the exhausted node
> case), but I think that shouldn't block the fix (and it does fix the
> issue we've run across in our testing).
> 

kmalloc_node(nid) and kmem_cache_alloc_node(nid) should fallback to nodes 
other than nid when memory can't be allocated, these functions only 
indicate a preference.