[PATCH] zoned vm counters: zone_reclaim: remove /proc/sys/vm/zone_reclaim_interval

The zone_reclaim_interval was necessary because we were not able to determine
how many unmapped pages exist in a zone.  Therefore we had to scan in
intervals to figure out if any pages were unmapped.

With the zoned counters and NR_ANON_PAGES we now know the number of pagecache
pages and the number of mapped pages in a zone.  So we can simply skip the
reclaim if there is an insufficient number of unmapped pages.  We use
SWAP_CLUSTER_MAX as the boundary.

Drop all support for /proc/sys/vm/zone_reclaim_interval.

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

5 files changed, 10 insertions, 50 deletions

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 2dc246af4885..86754eb390da 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -28,7 +28,6 @@ Currently, these files are in /proc/sys/vm:
 - block_dump
 - drop-caches
 - zone_reclaim_mode
-- zone_reclaim_interval
 - panic_on_oom
 
 ==============================================================
@@ -167,18 +166,6 @@ use of files and builds up large slab caches. However, the slab
 shrink operation is global, may take a long time and free slabs
 in all nodes of the system.
 
-================================================================
-
-zone_reclaim_interval:
-
-The time allowed for off node allocations after zone reclaim
-has failed to reclaim enough pages to allow a local allocation.
-
-Time is set in seconds and set by default to 30 seconds.
-
-Reduce the interval if undesired off node allocations occur. However, too
-frequent scans will have a negative impact onoff node allocation performance.
-
 =============================================================
 
 panic_on_oom
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 4833abd4458b..839e9a04fd49 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -178,12 +178,6 @@ struct zone {
 
         /* Zone statistics */
         atomic_long_t           vm_stat[NR_VM_ZONE_STAT_ITEMS];
-        /*
-         * 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
diff --git a/include/linux/swap.h b/include/linux/swap.h
index c41e2d6d1acc..cf6ca6e377bd 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -189,7 +189,6 @@ extern long vm_total_pages;
 
 #ifdef CONFIG_NUMA
 extern int zone_reclaim_mode;
-extern int zone_reclaim_interval;
 extern int zone_reclaim(struct zone *, gfp_t, unsigned int);
 #else
 #define zone_reclaim_mode 0
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 93a2c5398648..ee0db45e2438 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -933,15 +933,6 @@ static ctl_table vm_table[] = {
                 .strategy       = &sysctl_intvec,
                 .extra1         = &zero,
         },
-        {
-                .ctl_name       = VM_ZONE_RECLAIM_INTERVAL,
-                .procname       = "zone_reclaim_interval",
-                .data           = &zone_reclaim_interval,
-                .maxlen         = sizeof(zone_reclaim_interval),
-                .mode           = 0644,
-                .proc_handler   = &proc_dointvec_jiffies,
-                .strategy       = &sysctl_jiffies,
-        },
 #endif
 #ifdef CONFIG_X86_32
         {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2f0390161c0e..0960846d649f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1518,11 +1518,6 @@ int zone_reclaim_mode __read_mostly;
 #define RECLAIM_SLAB (1<<3)     /* Do a global slab shrink if the zone is out of memory */
 
 /*
- * Mininum time between zone reclaim scans
- */
-int zone_reclaim_interval __read_mostly = 30*HZ;
-
-/*
  * Priority for ZONE_RECLAIM. This determines the fraction of pages
  * of a node considered for each zone_reclaim. 4 scans 1/16th of
  * a zone.
@@ -1587,16 +1582,6 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 
         p->reclaim_state = NULL;
         current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
-
-        if (nr_reclaimed == 0) {
-                /*
-                 * We were unable to reclaim enough pages to stay on node.  We
-                 * now allow off node accesses for a certain time period before
-                 * trying again to reclaim pages from the local zone.
-                 */
-                zone->last_unsuccessful_zone_reclaim = jiffies;
-        }
-
         return nr_reclaimed >= nr_pages;
 }
 
@@ -1606,13 +1591,17 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
         int node_id;
 
         /*
-         * Do not reclaim if there was a recent unsuccessful attempt at zone
-         * reclaim.  In that case we let allocations go off node for the
-         * zone_reclaim_interval.  Otherwise we would scan for each off-node
-         * page allocation.
+         * Do not reclaim if there are not enough reclaimable pages in this
+         * zone that would satify this allocations.
+         *
+         * All unmapped pagecache pages are reclaimable.
+         *
+         * Both counters may be temporarily off a bit so we use
+         * SWAP_CLUSTER_MAX as the boundary. It may also be good to
+         * leave a few frequently used unmapped pagecache pages around.
          */
-        if (time_before(jiffies,
-                zone->last_unsuccessful_zone_reclaim + zone_reclaim_interval))
+        if (zone_page_state(zone, NR_FILE_PAGES) -
+                zone_page_state(zone, NR_FILE_MAPPED) < SWAP_CLUSTER_MAX)
                         return 0;
 
         /*