On Tue 18-02-14 17:43:38, David Rientjes wrote:

On Tue, 18 Feb 2014, Nishanth Aravamudan wrote:

quoted

How about the following?

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5de4337..1a0eced 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -1854,7 +1854,8 @@ static void __paginginit init_zone_allows_reclaim(int nid)
        int i;
 
        for_each_online_node(i)
-               if (node_distance(nid, i) <= RECLAIM_DISTANCE)
+               if (node_distance(nid, i) <= RECLAIM_DISTANCE ||
+                                       !NODE_DATA(i)->node_present_pages)
                        node_set(i, NODE_DATA(nid)->reclaim_nodes);
                else
                        zone_reclaim_mode = 1;

 [ I changed the above from NODE_DATA(nid) -> NODE_DATA(i) as you caught 
   so we're looking at the right code. ]

That can't be right, it would allow reclaiming from a memoryless node.  I 
think what you want is

	for_each_online_node(i) {
		if (!node_present_pages(i))
			continue;
		if (node_distance(nid, i) <= RECLAIM_DISTANCE) {
			node_set(i, NODE_DATA(nid)->reclaim_nodes);
			continue;
		}
		/* Always try to reclaim locally */
		zone_reclaim_mode = 1;
	}

but we really should be able to do for_each_node_state(i, N_MEMORY) here 
and memoryless nodes should already be excluded from that mask.

Agreed! Actually the code I am currently interested in is based on 3.0
kernel where zone_reclaim_mode is set in build_zonelists which relies on
find_next_best_node which iterates only N_HIGH_MEMORY nodes which should
have non 0 present pages.
[...]
-- 
Michal Hocko
SUSE Labs