mm/balloon_compaction.c: enqueue zero page to balloon device

presently pages in the balloon device have random value, and these pages
will be scanned by ksmd on the host.  They usually cannot be merged.
Enqueue zero pages will resolve this problem.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: zhenwei.pi <[email protected]>
Cc: Gioh Kim <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: Rafael Aquini <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/balloon_compaction.c

@@ -24,7 +24,7 @@ struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
 {
 	unsigned long flags;
 	struct page *page = alloc_page(balloon_mapping_gfp_mask() |
-					__GFP_NOMEMALLOC | __GFP_NORETRY);
+				__GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_ZERO);
 	if (!page)
 		return NULL;