On 05/07/2014 04:22 AM, David Rientjes wrote:
Async compaction terminates prematurely when need_resched(), see
compact_checklock_irqsave().  This can never trigger, however, if the
cond_resched() in isolate_migratepages_range() always takes care of the
scheduling.

If the cond_resched() actually triggers, then terminate this pageblock scan for
async compaction as well.

Signed-off-by: David Rientjes <rient...@google.com>

Acked-by: Vlastimil Babka <vba...@suse.cz>

---
  mm/compaction.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -500,8 +500,13 @@ isolate_migratepages_range(struct zone *zone, struct 
compact_control *cc,
                        return 0;
        }

+       if (cond_resched()) {
+               /* Async terminates prematurely on need_resched() */
+               if (cc->mode == MIGRATE_ASYNC)
+                       return 0;
+       }
+
        /* Time to isolate some pages for migration */
-       cond_resched();
        for (; low_pfn < end_pfn; low_pfn++) {
                /* give a chance to irqs before checking need_resched() */
                if (locked && !(low_pfn % SWAP_CLUSTER_MAX)) {


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