[PATCH 1/2] mm: compaction: try harder to isolate free pages

[Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>]

In isolate_freepages() check each page in a pageblock
instead of checking only first pages of pageblock_nr_pages
intervals (suitable_migration_target(page) is called before
isolate_freepages_block() so if page is "unsuitable" whole
pageblock_nr_pages pages will be ommited from the check).
It greatly improves possibility of finding free pages to
isolate during compaction_alloc() phase.

Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
---
 mm/compaction.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index d9ebebe..bc77135 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -65,7 +65,7 @@ static unsigned long isolate_freepages_block(struct zone *zone,
 
 	/* Get the last PFN we should scan for free pages at */
 	zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
-	end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
+	end_pfn = min(blockpfn + 1, zone_end_pfn);
 
 	/* Find the first usable PFN in the block to initialse page cursor */
 	for (; blockpfn < end_pfn; blockpfn++) {
@@ -160,8 +160,7 @@ static void isolate_freepages(struct zone *zone,
 	 * pages on cc->migratepages. We stop searching if the migrate
 	 * and free page scanners meet or enough free pages are isolated.
 	 */
-	for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
-					pfn -= pageblock_nr_pages) {
+	for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages; pfn--) {
 		unsigned long isolated;
 
 		if (!pfn_valid(pfn))
-- 
1.7.9.4

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