[PATCH] Zone reclaim: Reclaim logic

Some bits for zone reclaim exists in 2.6.15 but they are not usable.  This
patch fixes them up, removes unused code and makes zone reclaim usable.

Zone reclaim allows the reclaiming of pages from a zone if the number of
free pages falls below the watermarks even if other zones still have enough
pages available.  Zone reclaim is of particular importance for NUMA
machines.  It can be more beneficial to reclaim a page than taking the
performance penalties that come with allocating a page on a remote zone.

Zone reclaim is enabled if the maximum distance to another node is higher
than RECLAIM_DISTANCE, which may be defined by an arch.  By default
RECLAIM_DISTANCE is 20.  20 is the distance to another node in the same
component (enclosure or motherboard) on IA64.  The meaning of the NUMA
distance information seems to vary by arch.

If zone reclaim is not successful then no further reclaim attempts will
occur for a certain time period (ZONE_RECLAIM_INTERVAL).

This patch was discussed before. See

http://marc.theaimsgroup.com/?l=linux-kernel&m=113519961504207&w=2
http://marc.theaimsgroup.com/?l=linux-kernel&m=113408418232531&w=2
http://marc.theaimsgroup.com/?l=linux-kernel&m=113389027420032&w=2
http://marc.theaimsgroup.com/?l=linux-kernel&m=113380938612205&w=2

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c2e29743a8d1..df54e2fc8ee0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -878,7 +878,9 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order,
                                 mark = (*z)->pages_high;
                         if (!zone_watermark_ok(*z, order, mark,
                                     classzone_idx, alloc_flags))
-                                continue;
+                                if (!zone_reclaim_mode ||
+                                    !zone_reclaim(*z, gfp_mask, order))
+                                        continue;
                 }
 
                 page = buffered_rmqueue(zonelist, *z, order, gfp_mask);
@@ -1595,13 +1597,22 @@ static void __init build_zonelists(pg_data_t *pgdat)
         prev_node = local_node;
         nodes_clear(used_mask);
         while ((node = find_next_best_node(local_node, &used_mask)) >= 0) {
+                int distance = node_distance(local_node, node);
+
+                /*
+                 * If another node is sufficiently far away then it is better
+                 * to reclaim pages in a zone before going off node.
+                 */
+                if (distance > RECLAIM_DISTANCE)
+                        zone_reclaim_mode = 1;
+
                 /*
                  * We don't want to pressure a particular node.
                  * So adding penalty to the first node in same
                  * distance group to make it round-robin.
                  */
-                if (node_distance(local_node, node) !=
-                                node_distance(local_node, prev_node))
+
+                if (distance != node_distance(local_node, prev_node))
                         node_load[node] += load;
                 prev_node = node;
                 load--;