1 files changed, 55 insertions, 34 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index 20011a850fef..8fe917ec7c11 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -384,10 +384,62 @@ static int compact_finished(struct zone *zone,
         return COMPACT_CONTINUE;
 }
 
+/*
+ * compaction_suitable: Is this suitable to run compaction on this zone now?
+ * Returns
+ *   COMPACT_SKIPPED  - If there are too few free pages for compaction
+ *   COMPACT_PARTIAL  - If the allocation would succeed without compaction
+ *   COMPACT_CONTINUE - If compaction should run now
+ */
+unsigned long compaction_suitable(struct zone *zone, int order)
+{
+        int fragindex;
+        unsigned long watermark;
+
+        /*
+         * Watermarks for order-0 must be met for compaction. Note the 2UL.
+         * This is because during migration, copies of pages need to be
+         * allocated and for a short time, the footprint is higher
+         */
+        watermark = low_wmark_pages(zone) + (2UL << order);
+        if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
+                return COMPACT_SKIPPED;
+
+        /*
+         * fragmentation index determines if allocation failures are due to
+         * low memory or external fragmentation
+         *
+         * index of -1 implies allocations might succeed dependingon watermarks
+         * index towards 0 implies failure is due to lack of memory
+         * index towards 1000 implies failure is due to fragmentation
+         *
+         * Only compact if a failure would be due to fragmentation.
+         */
+        fragindex = fragmentation_index(zone, order);
+        if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
+                return COMPACT_SKIPPED;
+
+        if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0))
+                return COMPACT_PARTIAL;
+
+        return COMPACT_CONTINUE;
+}
+
 static int compact_zone(struct zone *zone, struct compact_control *cc)
 {
         int ret;
 
+        ret = compaction_suitable(zone, cc->order);
+        switch (ret) {
+        case COMPACT_PARTIAL:
+        case COMPACT_SKIPPED:
+                /* Compaction is likely to fail */
+                return ret;
+        case COMPACT_CONTINUE:
+                /* Fall through to compaction */
+                ;
+        }
+
         /* Setup to move all movable pages to the end of the zone */
         cc->migrate_pfn = zone->zone_start_pfn;
         cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
@@ -429,7 +481,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
         return ret;
 }
 
-static unsigned long compact_zone_order(struct zone *zone,
+unsigned long compact_zone_order(struct zone *zone,
                                                 int order, gfp_t gfp_mask)
 {
         struct compact_control cc = {
@@ -462,7 +514,6 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
         enum zone_type high_zoneidx = gfp_zone(gfp_mask);
         int may_enter_fs = gfp_mask & __GFP_FS;
         int may_perform_io = gfp_mask & __GFP_IO;
-        unsigned long watermark;
         struct zoneref *z;
         struct zone *zone;
         int rc = COMPACT_SKIPPED;
@@ -480,43 +531,13 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
         /* Compact each zone in the list */
         for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
                                                                 nodemask) {
-                int fragindex;
                 int status;
 
-                /*
-                 * Watermarks for order-0 must be met for compaction. Note
-                 * the 2UL. This is because during migration, copies of
-                 * pages need to be allocated and for a short time, the
-                 * footprint is higher
-                 */
-                watermark = low_wmark_pages(zone) + (2UL << order);
-                if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
-                        continue;
-
-                /*
-                 * fragmentation index determines if allocation failures are
-                 * due to low memory or external fragmentation
-                 *
-                 * index of -1 implies allocations might succeed depending
-                 *      on watermarks
-                 * index towards 0 implies failure is due to lack of memory
-                 * index towards 1000 implies failure is due to fragmentation
-                 *
-                 * Only compact if a failure would be due to fragmentation.
-                 */
-                fragindex = fragmentation_index(zone, order);
-                if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
-                        continue;
-
-                if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0)) {
-                        rc = COMPACT_PARTIAL;
-                        break;
-                }
-
                 status = compact_zone_order(zone, order, gfp_mask);
                 rc = max(status, rc);
 
-                if (zone_watermark_ok(zone, order, watermark, 0, 0))
+                /* If a normal allocation would succeed, stop compacting */
+                if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
                         break;
         }