mm/compaction.c: periodically schedule when freeing pages

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@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index c43789388cd8..b5326b141a25 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -677,6 +677,13 @@ static void isolate_freepages(struct zone *zone,
                                         pfn -= pageblock_nr_pages) {
                 unsigned long isolated;
 
+                /*
+                 * 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;