percpu: renew the max_contig if we merge the head and previous block

During pcpu_alloc_area(), we might merge the current head with the
previous block. Since we have calculated the max_contig using the
size of previous block before we skip it, and now we update the size
of previous block, so we should renew the max_contig.
Signed-off-by: NJianyu Zhan <nasa4836@gmail.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

mm/percpu.c

@@ -473,9 +473,11 @@ static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align)
 		 * uncommon for percpu allocations.
 		 */
 		if (head && (head < sizeof(int) || !(p[-1] & 1))) {
+			*p = off += head;
 			if (p[-1] & 1)
 				chunk->free_size -= head;
-			*p = off += head;
+			else
+				max_contig = max(*p - p[-1], max_contig);
 			this_size -= head;
 			head = 0;
 		}