[Devel] [PATCH rh7 01/25] ms/mm/compaction.c: periodically schedule when freeing pages

[Andrey Ryabinin]

From: David Rientjes <rientjes at google.com>

We've been getting warnings about an excessive amount of time spent
allocating pages for migration during memory compaction without
scheduling.  isolate_freepages_block() already periodically checks for
contended locks or the need to schedule, but isolate_freepages() never
does.

When a zone is massively long and no suitable targets can be found, this
iteration can be quite expensive without ever doing cond_resched().

Check periodically for the need to reschedule while the compaction free
scanner iterates.

Signed-off-by: David Rientjes <rientjes at google.com>
Reviewed-by: Rik van Riel <riel at redhat.com>
Reviewed-by: Wanpeng Li <liwanp at linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgorman at suse.de>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit f6ea3adb70b20ae36277a1b0eaaf4da9f6479a28)
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/compaction.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/compaction.c b/mm/compaction.c
index 63f5f4627ea7..f693bf3b87e2 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -698,6 +698,13 @@ static void isolate_freepages(struct zone *zone,
 		unsigned long isolated;
 		unsigned long end_pfn;
 
+		/*
+		 * This can iterate a massively long zone without finding any
+		 * suitable migration targets, so periodically check if we need
+		 * to schedule.
+		 */
+		cond_resched();
+
 		if (!pfn_valid(pfn))
 			continue;
 
-- 
2.13.6