---

yaml
---
r: 19374
b: refs/heads/master
c: 1b2ffb7
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 2a11ff06d7d12be5d1bbcf592fff649b45ac2388
+refs/heads/master: 1b2ffb7896ad46067f5b9ebf7de1891d74a4cdef

trunk/Documentation/sysctl/vm.txt

@@ -127,17 +127,39 @@ the high water marks for each per cpu page list.
 
 zone_reclaim_mode:
 
-This is set during bootup to 1 if it is determined that pages from
-remote zones will cause a significant performance reduction. The
+Zone_reclaim_mode allows to set more or less agressive approaches to
+reclaim memory when a zone runs out of memory. If it is set to zero then no
+zone reclaim occurs. Allocations will be satisfied from other zones / nodes
+in the system.
+
+This is value ORed together of
+
+1	= Zone reclaim on
+2	= Zone reclaim writes dirty pages out
+4	= Zone reclaim swaps pages
+
+zone_reclaim_mode is set during bootup to 1 if it is determined that pages
+from remote zones will cause a measurable performance reduction. The
 page allocator will then reclaim easily reusable pages (those page
-cache pages that are currently not used) before going off node.
+cache pages that are currently not used) before allocating off node pages.
+
+It may be beneficial to switch off zone reclaim if the system is
+used for a file server and all of memory should be used for caching files
+from disk. In that case the caching effect is more important than
+data locality.
+
+Allowing zone reclaim to write out pages stops processes that are
+writing large amounts of data from dirtying pages on other nodes. Zone
+reclaim will write out dirty pages if a zone fills up and so effectively
+throttle the process. This may decrease the performance of a single process
+since it cannot use all of system memory to buffer the outgoing writes
+anymore but it preserve the memory on other nodes so that the performance
+of other processes running on other nodes will not be affected.
 
-The user can override this setting. It may be beneficial to switch
-off zone reclaim if the system is used for a file server and all
-of memory should be used for caching files from disk.
+Allowing regular swap effectively restricts allocations to the local
+node unless explicitly overridden by memory policies or cpuset
+configurations.
 
-It may be beneficial to switch this on if one wants to do zone
-reclaim regardless of the numa distances in the system.
 ================================================================
 
 zone_reclaim_interval:

trunk/mm/vmscan.c

@@ -1592,6 +1592,11 @@ module_init(kswapd_init)
  */
 int zone_reclaim_mode __read_mostly;
 
+#define RECLAIM_OFF 0
+#define RECLAIM_ZONE (1<<0)	/* Run shrink_cache on the zone */
+#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
+#define RECLAIM_SWAP (1<<2)	/* Swap pages out during reclaim */
+
 /*
  * Mininum time between zone reclaim scans
  */
@@ -1630,8 +1635,8 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 	if (!cpus_empty(mask) && node_id != numa_node_id())
 		return 0;
 
-	sc.may_writepage = 0;
-	sc.may_swap = 0;
+	sc.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE);
+	sc.may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP);
 	sc.nr_scanned = 0;
 	sc.nr_reclaimed = 0;
 	sc.priority = ZONE_RECLAIM_PRIORITY + 1;