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

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.

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a596bfd..34a29e2 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2551,6 +2551,20 @@ 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 zone->pages_min. The memory within the
  * reserve will tend to store contiguous free pages. Setting min_free_kbytes
@@ -2579,7 +2593,7 @@ 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);