percpu: rename pcpu_mem_alloc to pcpu_mem_zalloc

Currently pcpu_mem_alloc() is implemented always return zeroed memory.
So rename it to make user like pcpu_get_pages_and_bitmap() know don't
reinit it.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
index ea53496..29e3730 100644
--- a/mm/percpu-vm.c
+++ b/mm/percpu-vm.c
@@ -50,14 +50,13 @@
 
 	if (!pages || !bitmap) {
 		if (may_alloc && !pages)
-			pages = pcpu_mem_alloc(pages_size);
+			pages = pcpu_mem_zalloc(pages_size);
 		if (may_alloc && !bitmap)
-			bitmap = pcpu_mem_alloc(bitmap_size);
+			bitmap = pcpu_mem_zalloc(bitmap_size);
 		if (!pages || !bitmap)
 			return NULL;
 	}
 
-	memset(pages, 0, pages_size);
 	bitmap_copy(bitmap, chunk->populated, pcpu_unit_pages);
 
 	*bitmapp = bitmap;