mm: fix return type for functions nr_free_*_pages

Currently, the amount of RAM that functions nr_free_*_pages return is
held in unsigned int.  But in machines with big memory (exceeding 16TB),
the amount may be incorrect because of overflow, so fix it.
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Simon Horman <horms@verge.net.au>
Cc: Julian Anastasov <ja@ssi.bg>
Cc: David Miller <davem@davemloft.net>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Minchan Kim <minchan.kim@gmail.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>

include/linux/swap.h

@@ -225,8 +225,8 @@ struct swap_list_t {
 extern unsigned long totalram_pages;
 extern unsigned long totalreserve_pages;
 extern unsigned long dirty_balance_reserve;
-extern unsigned int nr_free_buffer_pages(void);
-extern unsigned int nr_free_pagecache_pages(void);
+extern unsigned long nr_free_buffer_pages(void);
+extern unsigned long nr_free_pagecache_pages(void);
 
 /* Definition of global_page_state not available yet */
 #define nr_free_pages() global_page_state(NR_FREE_PAGES)

mm/page_alloc.c

@@ -2813,13 +2813,13 @@ void free_pages_exact(void *virt, size_t size)
 }
 EXPORT_SYMBOL(free_pages_exact);
 
-static unsigned int nr_free_zone_pages(int offset)
+static unsigned long nr_free_zone_pages(int offset)
 {
 	struct zoneref *z;
 	struct zone *zone;
 
 	/* Just pick one node, since fallback list is circular */
-	unsigned int sum = 0;
+	unsigned long sum = 0;
 
 	struct zonelist *zonelist = node_zonelist(numa_node_id(), GFP_KERNEL);
 
@@ -2836,7 +2836,7 @@ static unsigned int nr_free_zone_pages(int offset)
 /*
  * Amount of free RAM allocatable within ZONE_DMA and ZONE_NORMAL
  */
-unsigned int nr_free_buffer_pages(void)
+unsigned long nr_free_buffer_pages(void)
 {
 	return nr_free_zone_pages(gfp_zone(GFP_USER));
 }
@@ -2845,7 +2845,7 @@ EXPORT_SYMBOL_GPL(nr_free_buffer_pages);
 /*
  * Amount of free RAM allocatable within all zones
  */
-unsigned int nr_free_pagecache_pages(void)
+unsigned long nr_free_pagecache_pages(void)
 {
 	return nr_free_zone_pages(gfp_zone(GFP_HIGHUSER_MOVABLE));
 }