1 files changed, 54 insertions, 22 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index 021a2960ef9e..6cc604bd5649 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -144,9 +144,20 @@ static void isolate_freepages(struct zone *zone,
         int nr_freepages = cc->nr_freepages;
         struct list_head *freelist = &cc->freepages;
 
+        /*
+         * Initialise the free scanner. The starting point is where we last
+         * scanned from (or the end of the zone if starting). The low point
+         * is the end of the pageblock the migration scanner is using.
+         */
         pfn = cc->free_pfn;
         low_pfn = cc->migrate_pfn + pageblock_nr_pages;
-        high_pfn = low_pfn;
+
+        /*
+         * Take care that if the migration scanner is at the end of the zone
+         * that the free scanner does not accidentally move to the next zone
+         * in the next isolation cycle.
+         */
+        high_pfn = min(low_pfn, pfn);
 
         /*
          * Isolate free pages until enough are available to migrate the
@@ -240,11 +251,18 @@ static bool too_many_isolated(struct zone *zone)
         return isolated > (inactive + active) / 2;
 }
 
+/* possible outcome of isolate_migratepages */
+typedef enum {
+        ISOLATE_ABORT,          /* Abort compaction now */
+        ISOLATE_NONE,           /* No pages isolated, continue scanning */
+        ISOLATE_SUCCESS,        /* Pages isolated, migrate */
+} isolate_migrate_t;
+
 /*
  * Isolate all pages that can be migrated from the block pointed to by
  * the migrate scanner within compact_control.
  */
-static unsigned long isolate_migratepages(struct zone *zone,
+static isolate_migrate_t isolate_migratepages(struct zone *zone,
                                         struct compact_control *cc)
 {
         unsigned long low_pfn, end_pfn;
@@ -261,7 +279,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
         /* Do not cross the free scanner or scan within a memory hole */
         if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
                 cc->migrate_pfn = end_pfn;
-                return 0;
+                return ISOLATE_NONE;
         }
 
         /*
@@ -270,10 +288,14 @@ static unsigned long isolate_migratepages(struct zone *zone,
          * delay for some time until fewer pages are isolated
          */
         while (unlikely(too_many_isolated(zone))) {
+                /* async migration should just abort */
+                if (!cc->sync)
+                        return ISOLATE_ABORT;
+
                 congestion_wait(BLK_RW_ASYNC, HZ/10);
 
                 if (fatal_signal_pending(current))
-                        return 0;
+                        return ISOLATE_ABORT;
         }
 
         /* Time to isolate some pages for migration */
@@ -358,7 +380,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
 
         trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
 
-        return cc->nr_migratepages;
+        return ISOLATE_SUCCESS;
 }
 
 /*
@@ -420,13 +442,6 @@ static int compact_finished(struct zone *zone,
         if (cc->free_pfn <= cc->migrate_pfn)
                 return COMPACT_COMPLETE;
 
-        /* Compaction run is not finished if the watermark is not met */
-        watermark = low_wmark_pages(zone);
-        watermark += (1 << cc->order);
-
-        if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
-                return COMPACT_CONTINUE;
-
         /*
          * order == -1 is expected when compacting via
          * /proc/sys/vm/compact_memory
@@ -434,6 +449,13 @@ static int compact_finished(struct zone *zone,
         if (cc->order == -1)
                 return COMPACT_CONTINUE;
 
+        /* Compaction run is not finished if the watermark is not met */
+        watermark = low_wmark_pages(zone);
+        watermark += (1 << cc->order);
+
+        if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
+                return COMPACT_CONTINUE;
+
         /* Direct compactor: Is a suitable page free? */
         for (order = cc->order; order < MAX_ORDER; order++) {
                 /* Job done if page is free of the right migratetype */
@@ -461,6 +483,13 @@ unsigned long compaction_suitable(struct zone *zone, int order)
         unsigned long watermark;
 
         /*
+         * order == -1 is expected when compacting via
+         * /proc/sys/vm/compact_memory
+         */
+        if (order == -1)
+                return COMPACT_CONTINUE;
+
+        /*
          * 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
@@ -470,17 +499,11 @@ unsigned long compaction_suitable(struct zone *zone, int order)
                 return COMPACT_SKIPPED;
 
         /*
-         * order == -1 is expected when compacting via
-         * /proc/sys/vm/compact_memory
-         */
-        if (order == -1)
-                return COMPACT_CONTINUE;
-
-        /*
          * fragmentation index determines if allocation failures are due to
          * low memory or external fragmentation
          *
-         * index of -1 implies allocations might succeed dependingon watermarks
+         * index of -1000 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
          *
@@ -490,7 +513,8 @@ unsigned long compaction_suitable(struct zone *zone, int order)
         if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
                 return COMPACT_SKIPPED;
 
-        if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0))
+        if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
+            0, 0))
                 return COMPACT_PARTIAL;
 
         return COMPACT_CONTINUE;
@@ -522,8 +546,15 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
                 unsigned long nr_migrate, nr_remaining;
                 int err;
 
-                if (!isolate_migratepages(zone, cc))
+                switch (isolate_migratepages(zone, cc)) {
+                case ISOLATE_ABORT:
+                        ret = COMPACT_PARTIAL;
+                        goto out;
+                case ISOLATE_NONE:
                         continue;
+                case ISOLATE_SUCCESS:
+                        ;
+                }
 
                 nr_migrate = cc->nr_migratepages;
                 err = migrate_pages(&cc->migratepages, compaction_alloc,
@@ -547,6 +578,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
 
         }
 
+out:
         /* Release free pages and check accounting */
         cc->nr_freepages -= release_freepages(&cc->freepages);
         VM_BUG_ON(cc->nr_freepages != 0);