mm: move zone watermark accesses behind an accessor

This is a preparation patch only, no functional change.

Link: http://lkml.kernel.org/r/20181123114528.28802-3-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmzone.h

@@ -269,9 +269,10 @@ enum zone_watermarks {
 	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])
+#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])
+#define wmark_pages(z, i) (z->_watermark[i])
 
 struct per_cpu_pages {
 	int count;		/* number of pages in the list */
@@ -362,7 +363,7 @@ struct zone {
 	/* Read-mostly fields */
 
 	/* zone watermarks, access with *_wmark_pages(zone) macros */
-	unsigned long watermark[NR_WMARK];
+	unsigned long _watermark[NR_WMARK];
 
 	unsigned long nr_reserved_highatomic;
 

mm/compaction.c

@@ -1431,7 +1431,7 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
 	if (is_via_compact_memory(order))
 		return COMPACT_CONTINUE;
 
-	watermark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
+	watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
 	/*
 	 * If watermarks for high-order allocation are already met, there
 	 * should be no need for compaction at all.

mm/page_alloc.c

@@ -3376,7 +3376,7 @@ retry:
 			}
 		}
 
-		mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
+		mark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
 		if (!zone_watermark_fast(zone, order, mark,
 				       ac_classzone_idx(ac), alloc_flags)) {
 			int ret;
@@ -4793,7 +4793,7 @@ long si_mem_available(void)
 		pages[lru] = global_node_page_state(NR_LRU_BASE + lru);
 
 	for_each_zone(zone)
-		wmark_low += zone->watermark[WMARK_LOW];
+		wmark_low += low_wmark_pages(zone);
 
 	/*
 	 * Estimate the amount of memory available for userspace allocations,
@@ -7431,13 +7431,13 @@ static void __setup_per_zone_wmarks(void)
 
 			min_pages = zone_managed_pages(zone) / 1024;
 			min_pages = clamp(min_pages, SWAP_CLUSTER_MAX, 128UL);
-			zone->watermark[WMARK_MIN] = min_pages;
+			zone->_watermark[WMARK_MIN] = min_pages;
 		} else {
 			/*
 			 * If it's a lowmem zone, reserve a number of pages
 			 * proportionate to the zone's size.
 			 */
-			zone->watermark[WMARK_MIN] = tmp;
+			zone->_watermark[WMARK_MIN] = tmp;
 		}
 
 		/*
@@ -7449,8 +7449,8 @@ static void __setup_per_zone_wmarks(void)
 			    mult_frac(zone_managed_pages(zone),
 				      watermark_scale_factor, 10000));
 
-		zone->watermark[WMARK_LOW]  = min_wmark_pages(zone) + tmp;
-		zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2;
+		zone->_watermark[WMARK_LOW]  = min_wmark_pages(zone) + tmp;
+		zone->_watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2;
 
 		spin_unlock_irqrestore(&zone->lock, flags);
 	}