mm/page_alloc: remove realsize in free_area_init_core()

Highmem's realsize always equals to freesize, so it is not necessary to
spare a variable to record this.

Link: http://lkml.kernel.org/r/20180413083859.65888-1-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: RichardWeiYang

mm/page_alloc.c

@@ -6229,18 +6229,18 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
 
 	for (j = 0; j < MAX_NR_ZONES; j++) {
 		struct zone *zone = pgdat->node_zones + j;
-		unsigned long size, realsize, freesize, memmap_pages;
+		unsigned long size, freesize, memmap_pages;
 		unsigned long zone_start_pfn = zone->zone_start_pfn;
 
 		size = zone->spanned_pages;
-		realsize = freesize = zone->present_pages;
+		freesize = zone->present_pages;
 
 		/*
 		 * Adjust freesize so that it accounts for how much memory
 		 * is used by this zone for memmap. This affects the watermark
 		 * and per-cpu initialisations
 		 */
-		memmap_pages = calc_memmap_size(size, realsize);
+		memmap_pages = calc_memmap_size(size, freesize);
 		if (!is_highmem_idx(j)) {
 			if (freesize >= memmap_pages) {
 				freesize -= memmap_pages;
@@ -6272,7 +6272,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
 		 * when the bootmem allocator frees pages into the buddy system.
 		 * And all highmem pages will be managed by the buddy system.
 		 */
-		zone->managed_pages = is_highmem_idx(j) ? realsize : freesize;
+		zone->managed_pages = freesize;
 #ifdef CONFIG_NUMA
 		zone->node = nid;
 #endif