[PATCH 6/6] mm: compaction: skip fast freepages isolation if enough freepages are isolated

[Baolin Wang <baolin.wang@linux.alibaba.com>]

I've observed that fast isolation often isolates more pages than
cc->migratepages, and the excess freepages will be released back to the
buddy system. So skip fast freepages isolation if enough freepages are
isolated to save some CPU cycles.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 mm/compaction.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/compaction.c b/mm/compaction.c
index eccec84dae82..3ade4c095ed2 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1550,6 +1550,10 @@ static void fast_isolate_freepages(struct compact_control *cc)
 
 		spin_unlock_irqrestore(&cc->zone->lock, flags);
 
+		/* Skip fast search if enough freepages isolated */
+		if (cc->nr_freepages >= cc->nr_migratepages)
+			break;
+
 		/*
 		 * Smaller scan on next order so the total scan is related
 		 * to freelist_scan_limit.
-- 
2.27.0