page-allocator: change migratetype for all pageblocks within a high-order page during...

When there are no pages of a target migratetype free, the page allocator
selects a high-order block of another migratetype to allocate from.  When
the order of the page taken is greater than pageblock_order, all
pageblocks within that high-order page should change migratetype so that
pages are later freed to the correct free-lists.

The current behaviour is that pageblocks change migratetype if the order
being split matches the pageblock_order.  When pageblock_order <
MAX_ORDER-1, ownership is not changing correct and pages are being later
freed to the incorrect list and this impacts fragmentation avoidance.

This patch changes all pageblocks within the high-order page being split
to the correct migratetype.  Without the patch, allocation success rates
for hugepages under stress were about 59% of physical memory on x86-64.
With the patch applied, this goes up to 65%.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9242d13..2075980 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -783,6 +783,17 @@ static int move_freepages_block(struct zone *zone, struct page *page,
        return move_freepages(zone, start_page, end_page, migratetype);
 }
 
+static void change_pageblock_range(struct page *pageblock_page,
+                                       int start_order, int migratetype)
+{
+       int nr_pageblocks = 1 << (start_order - pageblock_order);
+
+       while (nr_pageblocks--) {
+               set_pageblock_migratetype(pageblock_page, migratetype);
+               pageblock_page += pageblock_nr_pages;
+       }
+}
+
 /* Remove an element from the buddy allocator from the fallback list */
 static inline struct page *
 __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
@@ -836,8 +847,9 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
                        list_del(&page->lru);
                        rmv_page_order(page);
 
-                       if (current_order == pageblock_order)
-                               set_pageblock_migratetype(page,
+                       /* Take ownership for orders >= pageblock_order */
+                       if (current_order >= pageblock_order)
+                               change_pageblock_range(page, current_order,
                                                        start_migratetype);
 
                        expand(zone, page, order, current_order, area, migratetype);