mm: cma: skip watermarks check for already isolated blocks in split_free_page()

Since commit 2139cbe627b8 ("cma: fix counting of isolated pages") free
pages in isolated pageblocks are not accounted to NR_FREE_PAGES counters,
so watermarks check is not required if one operates on a free page in
isolated pageblock.

Change-Id: Id9b38d2e4e504336e11274a30044e3aacbc37d03
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Mel Gorman <mel@csn.ul.ie>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 2e30abd1730751d58463d88bc0844ab8fd7112a9
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
[lauraa@codeaurora.org: Context fixups due to being merged
out of order. Bring over an added 'feature' where we don't
obey watermarks for CMA pages]
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 54b1faf..ca215b3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1459,20 +1459,20 @@
 	order = page_order(page);
 	mt = get_pageblock_migratetype(page);
 
-	/* Obey watermarks as if the page was being allocated */
-	watermark = low_wmark_pages(zone) + (1 << order);
-	if (!is_migrate_cma(mt) && mt != MIGRATE_ISOLATE &&
-	    !zone_watermark_ok(zone, 0, watermark, 0, 0))
-		return 0;
+	if (mt != MIGRATE_ISOLATE && !is_migrate_cma(mt)) {
+		/* Obey watermarks as if the page was being allocated */
+		watermark = low_wmark_pages(zone) + (1 << order);
+		if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
+			return 0;
+
+		__mod_zone_freepage_state(zone, -(1UL << alloc_order), mt);
+	}
 
 	/* Remove page from free list */
 	list_del(&page->lru);
 	zone->free_area[order].nr_free--;
 	rmv_page_order(page);
 
-	if (unlikely(mt != MIGRATE_ISOLATE))
-		__mod_zone_freepage_state(zone, -(1UL << order), mt);
-
 	if (alloc_order != order)
 		expand(zone, page, alloc_order, order,
 			&zone->free_area[order], migratetype);