[PATCH] mm: Check if any page in a pageblock is reserved before marking it MIGRATE_RESERVE

[John Stultz <john.stultz@linaro.org>]

From: Arve Hjønnevåg <arve@android.com>

This fixes a problem where the first pageblock got marked MIGRATE_RESERVE even
though it only had a few free pages. This in turn caused no contiguous memory
to be reserved and frequent kswapd wakeups that emptied the caches to get more
contiguous memory.

CC: Dave Hansen <dave@linux.vnet.ibm.com>
CC: Mel Gorman <mgorman@suse.de>
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Arve Hjønnevåg <arve@android.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>

[This patch was submitted and acked a little over a year ago
(see: http://lkml.org/lkml/2010/4/6/172 ), but never seemingly
made it upstream. Resending for comments. -jstultz]

Signed-off-by: John Stultz <john.stultz@linaro.org>
---
 mm/page_alloc.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ed87f3b..209d9bf 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3288,6 +3288,20 @@ static inline unsigned long wait_table_bits(unsigned long size)
 #define LONG_ALIGN(x) (((x)+(sizeof(long))-1)&~((sizeof(long))-1))
 
 /*
+ * Check if a pageblock contains reserved pages
+ */
+static int pageblock_is_reserved(unsigned long start_pfn)
+{
+	unsigned long end_pfn = start_pfn + pageblock_nr_pages;
+	unsigned long pfn;
+
+	for (pfn = start_pfn; pfn < end_pfn; pfn++)
+		if (PageReserved(pfn_to_page(pfn)))
+			return 1;
+	return 0;
+}
+
+/*
  * Mark a number of pageblocks as MIGRATE_RESERVE. The number
  * of blocks reserved is based on min_wmark_pages(zone). The memory within
  * the reserve will tend to store contiguous free pages. Setting min_free_kbytes
@@ -3326,7 +3340,7 @@ static void setup_zone_migrate_reserve(struct zone *zone)
 			continue;
 
 		/* Blocks with reserved pages will never free, skip them. */
-		if (PageReserved(page))
+		if (pageblock_is_reserved(pfn))
 			continue;
 
 		block_migratetype = get_pageblock_migratetype(page);
-- 
1.7.3.2.146.gca209