[Qemu-devel] [PATCH 4/9] mm: compaction: Abort compaction loop if lock is contended or run too long

[Mel Gorman]

From: Shaohua Li <address@hidden>

Changelog since V2
o Fix BUG_ON triggered due to pages left on cc.migratepages
o Make compact_zone_order() require non-NULL arg `contended'

Changelog since V1
o only abort the compaction if lock is contended or run too long
o Rearranged the code by Andrea Arcangeli.

isolate_migratepages_range() might isolate no pages if for example when
zone->lru_lock is contended and running asynchronous compaction. In this
case, we should abort compaction, otherwise, compact_zone will run a
useless loop and make zone->lru_lock is even contended.

address@hidden: Putback pages isolated for migration if aborting]
address@hidden: compact_zone_order requires non-NULL arg contended]
Signed-off-by: Andrea Arcangeli <address@hidden>
Signed-off-by: Shaohua Li <address@hidden>
Signed-off-by: Mel Gorman <address@hidden>
Acked-by: Rik van Riel <address@hidden>
---
 mm/compaction.c |   17 ++++++++++++-----
 mm/internal.h   |    2 +-
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 614f18b..6b55491 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -70,8 +70,7 @@ static bool compact_checklock_irqsave(spinlock_t *lock, 
unsigned long *flags,
 
                /* async aborts if taking too long or contended */
                if (!cc->sync) {
-                       if (cc->contended)
-                               *cc->contended = true;
+                       cc->contended = true;
                        return false;
                }
 
@@ -686,7 +685,7 @@ static isolate_migrate_t isolate_migratepages(struct zone 
*zone,
 
        /* Perform the isolation */
        low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
-       if (!low_pfn)
+       if (!low_pfn || cc->contended)
                return ISOLATE_ABORT;
 
        cc->migrate_pfn = low_pfn;
@@ -846,6 +845,8 @@ static int compact_zone(struct zone *zone, struct 
compact_control *cc)
                switch (isolate_migratepages(zone, cc)) {
                case ISOLATE_ABORT:
                        ret = COMPACT_PARTIAL;
+                       putback_lru_pages(&cc->migratepages);
+                       cc->nr_migratepages = 0;
                        goto out;
                case ISOLATE_NONE:
                        continue;
@@ -894,6 +895,7 @@ static unsigned long compact_zone_order(struct zone *zone,
                                 bool sync, bool *contended,
                                 struct page **page)
 {
+       unsigned long ret;
        struct compact_control cc = {
                .nr_freepages = 0,
                .nr_migratepages = 0,
@@ -901,13 +903,18 @@ static unsigned long compact_zone_order(struct zone *zone,
                .migratetype = allocflags_to_migratetype(gfp_mask),
                .zone = zone,
                .sync = sync,
-               .contended = contended,
                .page = page,
        };
        INIT_LIST_HEAD(&cc.freepages);
        INIT_LIST_HEAD(&cc.migratepages);
 
-       return compact_zone(zone, &cc);
+       ret = compact_zone(zone, &cc);
+
+       VM_BUG_ON(!list_empty(&cc.freepages));
+       VM_BUG_ON(!list_empty(&cc.migratepages));
+
+       *contended = cc.contended;
+       return ret;
 }
 
 int sysctl_extfrag_threshold = 500;
diff --git a/mm/internal.h b/mm/internal.h
index 386772f..eebbed5 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -131,7 +131,7 @@ struct compact_control {
        int order;                      /* order a direct compactor needs */
        int migratetype;                /* MOVABLE, RECLAIMABLE etc */
        struct zone *zone;
-       bool *contended;                /* True if a lock was contended */
+       bool contended;                 /* True if a lock was contended */
        struct page **page;             /* Page captured of requested size */
 };
 
-- 
1.7.9.2