dm bufio: remove redundant __GFP_NOWARN

GFP_NOWAIT already includes __GFP_NOWARN, so let's remove the redundant
__GFP_NOWARN.  Also update comments to clarify the flag semantics.

Signed-off-by: Qianfeng Rong <rongqianfeng@vivo.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Author: qianfengrong

drivers/md/dm-bufio.c

@@ -1337,7 +1337,7 @@ static void use_bio(struct dm_buffer *b, enum req_op op, sector_t sector,
 	char *ptr;
 	unsigned int len;
 
-	bio = bio_kmalloc(1, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOWARN);
+	bio = bio_kmalloc(1, GFP_NOWAIT);
 	if (!bio) {
 		use_dmio(b, op, sector, n_sectors, offset, ioprio);
 		return;
@@ -1601,18 +1601,18 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
 	 * dm-bufio is resistant to allocation failures (it just keeps
 	 * one buffer reserved in cases all the allocations fail).
 	 * So set flags to not try too hard:
-	 *	GFP_NOWAIT: don't wait; if we need to sleep we'll release our
-	 *		    mutex and wait ourselves.
+	 *	GFP_NOWAIT: don't wait and don't print a warning in case of
+	 *		    failure; if we need to sleep we'll release our mutex
+	 *		    and wait ourselves.
 	 *	__GFP_NORETRY: don't retry and rather return failure
 	 *	__GFP_NOMEMALLOC: don't use emergency reserves
-	 *	__GFP_NOWARN: don't print a warning in case of failure
 	 *
 	 * For debugging, if we set the cache size to 1, no new buffers will
 	 * be allocated.
 	 */
 	while (1) {
 		if (dm_bufio_cache_size_latch != 1) {
-			b = alloc_buffer(c, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			b = alloc_buffer(c, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOMEMALLOC);
 			if (b)
 				return b;
 		}