On Mon, 11 Aug 2014, Vladimir Davydov wrote:

quoted

diff --git a/mm/slab.c b/mm/slab.c
--- a/mm/slab.c
+++ b/mm/slab.c

@@ -3047,16 +3047,19 @@ retry:
 	 * from existing per node queues.
 	 */
 	for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
-		nid = zone_to_nid(zone);
+		struct kmem_cache_node *n;
 
-		if (cpuset_zone_allowed_hardwall(zone, flags) &&
-			get_node(cache, nid) &&
-			get_node(cache, nid)->free_objects) {
-				obj = ____cache_alloc_node(cache,
-					flags | GFP_THISNODE, nid);
-				if (obj)
-					break;
-		}
+		nid = zone_to_nid(zone);
+		if (!cpuset_zone_allowed(zone, flags | __GFP_HARDWALL))

We must use softwall check here, otherwise we will proceed to
alloc_pages even if there are lots of free slabs on other nodes.
alloc_pages, in turn, may allocate from other nodes in case
cpuset.mem_hardwall=0, because it uses softwall check, so it may add yet
another free slab to another node's list even if it isn't empty. As a
result, we may get free list bloating on other nodes. I've seen a
machine with one of its nodes almost completely filled with inactive
slabs for buffer_heads (dozens of GBs) w/o any chance to drop them. So,
this is a bug that must be fixed.

Right, I understand, and my patch makes no attempt to fix that issue, it's 
simply collapsing the code down into a single cpuset_zone_allowed() 
function and the context for the allocation is controlled by the gfp 
flags (and hardwall is controlled by setting __GFP_HARDWALL) as it should 
be.  I understand the issue you face, but I can't combine a cleanup with a 
fix and I would prefer to have your patch keep your commit description.  

The diffstat for my proposal removes many more lines than it adds and I 
think it will avoid this type of issue in the future for new callers.  
Your patch could then be based on the single cpuset_zone_allowed() 
function where you would simply have to remove the __GFP_HARDWALL above.  
Or, your patch could be merged first and then my cleanup on top, but it 
seems like your one-liner would be more clear if it is based on mine.

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