4 files changed, 44 insertions, 1 deletions

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 56dd29b97a91..5fdbb612aeb8 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -27,6 +27,7 @@ Currently, these files are in /proc/sys/vm:
 - dirty_ratio
 - dirty_writeback_centisecs
 - drop_caches
+- extfrag_threshold
 - hugepages_treat_as_movable
 - hugetlb_shm_group
 - laptop_mode
@@ -149,6 +150,20 @@ user should run `sync' first.
 
 ==============================================================
 
+extfrag_threshold
+
+This parameter affects whether the kernel will compact memory or direct
+reclaim to satisfy a high-order allocation. /proc/extfrag_index shows what
+the fragmentation index for each order is in each zone in the system. Values
+tending towards 0 imply allocations would fail due to lack of memory,
+values towards 1000 imply failures are due to fragmentation and -1 implies
+that the allocation will succeed as long as watermarks are met.
+
+The kernel will not compact memory in a zone if the
+fragmentation index is <= extfrag_threshold. The default value is 500.
+
+==============================================================
+
 hugepages_treat_as_movable
 
 This parameter is only useful when kernelcore= is specified at boot time to
diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index eed40ec4280b..3719325c6091 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -15,6 +15,9 @@
 extern int sysctl_compact_memory;
 extern int sysctl_compaction_handler(struct ctl_table *table, int write,
                         void __user *buffer, size_t *length, loff_t *ppos);
+extern int sysctl_extfrag_threshold;
+extern int sysctl_extfrag_handler(struct ctl_table *table, int write,
+                        void __user *buffer, size_t *length, loff_t *ppos);
 
 extern int fragmentation_index(struct zone *zone, unsigned int order);
 extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 284f330d6a01..84ff5e75c084 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -263,6 +263,11 @@ static int min_sched_shares_ratelimit = 100000; /* 100 usec */
 static int max_sched_shares_ratelimit = NSEC_PER_SEC; /* 1 second */
 #endif
 
+#ifdef CONFIG_COMPACTION
+static int min_extfrag_threshold;
+static int max_extfrag_threshold = 1000;
+#endif
+
 static struct ctl_table kern_table[] = {
         {
                 .procname       = "sched_child_runs_first",
@@ -1130,6 +1135,16 @@ static struct ctl_table vm_table[] = {
                 .mode           = 0200,
                 .proc_handler   = sysctl_compaction_handler,
         },
+        {
+                .procname       = "extfrag_threshold",
+                .data           = &sysctl_extfrag_threshold,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = sysctl_extfrag_handler,
+                .extra1         = &min_extfrag_threshold,
+                .extra2         = &max_extfrag_threshold,
+        },
+
 #endif /* CONFIG_COMPACTION */
         {
                 .procname       = "min_free_kbytes",
diff --git a/mm/compaction.c b/mm/compaction.c
index 9583e193dc47..94cce51b0b35 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -433,6 +433,8 @@ static unsigned long compact_zone_order(struct zone *zone,
         return compact_zone(zone, &cc);
 }
 
+int sysctl_extfrag_threshold = 500;
+
 /**
  * try_to_compact_pages - Direct compact to satisfy a high-order allocation
  * @zonelist: The zonelist used for the current allocation
@@ -491,7 +493,7 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
                  * Only compact if a failure would be due to fragmentation.
                  */
                 fragindex = fragmentation_index(zone, order);
-                if (fragindex >= 0 && fragindex <= 500)
+                if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
                         continue;
 
                 if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0)) {
@@ -572,6 +574,14 @@ int sysctl_compaction_handler(struct ctl_table *table, int write,
         return 0;
 }
 
+int sysctl_extfrag_handler(struct ctl_table *table, int write,
+                        void __user *buffer, size_t *length, loff_t *ppos)
+{
+        proc_dointvec_minmax(table, write, buffer, length, ppos);
+
+        return 0;
+}
+
 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
 ssize_t sysfs_compact_node(struct sys_device *dev,
                         struct sysdev_attribute *attr,