page allocator: use allocation flags as an index to the zone watermark

ALLOC_WMARK_MIN, ALLOC_WMARK_LOW and ALLOC_WMARK_HIGH determin whether
pages_min, pages_low or pages_high is used as the zone watermark when
allocating the pages.  Two branches in the allocator hotpath determine
which watermark to use.

This patch uses the flags as an array index into a watermark array that is
indexed with WMARK_* defines accessed via helpers.  All call sites that
use zone->pages_* are updated to use the helpers for accessing the values
and the array offsets for setting.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0aa4445b0b8..dd8487f0442 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -163,6 +163,17 @@ static inline int is_unevictable_lru(enum lru_list l)
 #endif
 }
 
+enum zone_watermarks {
+        WMARK_MIN,
+        WMARK_LOW,
+        WMARK_HIGH,
+        NR_WMARK
+};
+
+#define min_wmark_pages(z) (z->watermark[WMARK_MIN])
+#define low_wmark_pages(z) (z->watermark[WMARK_LOW])
+#define high_wmark_pages(z) (z->watermark[WMARK_HIGH])
+
 struct per_cpu_pages {
         int count;              /* number of pages in the list */
         int high;               /* high watermark, emptying needed */
@@ -275,7 +286,10 @@ struct zone_reclaim_stat {
 
 struct zone {
         /* Fields commonly accessed by the page allocator */
-        unsigned long           pages_min, pages_low, pages_high;
+
+        /* zone watermarks, access with *_wmark_pages(zone) macros */
+        unsigned long watermark[NR_WMARK];
+
         /*
          * We don't know if the memory that we're going to allocate will be freeable
          * or/and it will be released eventually, so to avoid totally wasting several