[patch v3 6/6] mm, compaction: terminate async compaction when rescheduling

[David Rientjes]

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 <rientjes@xxxxxxxxxx>
---
 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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