[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, 7 insertions, 5 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 34cbefd2ebde..93a849f742db 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -149,15 +149,17 @@ struct zone {
         unsigned long           pages_scanned;     /* since last reclaim */
         int                     all_unreclaimable; /* All pages pinned */
 
-        /*
-         * Does the allocator try to reclaim pages from the zone as soon
-         * as it fails a watermark_ok() in __alloc_pages?
-         */
-        int                     reclaim_pages;
         /* A count of how many reclaimers are scanning this zone */
         atomic_t                reclaim_in_progress;
 
         /*
+         * timestamp (in jiffies) of the last zone reclaim that did not
+         * result in freeing of pages. This is used to avoid repeated scans
+         * if all memory in the zone is in use.
+         */
+        unsigned long           last_unsuccessful_zone_reclaim;
+
+        /*
          * prev_priority holds the scanning priority for this zone.  It is
          * defined as the scanning priority at which we achieved our reclaim
          * target at the previous try_to_free_pages() or balance_pgdat()