ext4: make xattr inode reads faster

ext4_xattr_inode_read() currently reads each block sequentially while
waiting for io operation to complete before moving on to the next
block. This prevents request merging in block layer.

Add a ext4_bread_batch() function that starts reads for all blocks
then optionally waits for them to complete. A similar logic is used
in ext4_find_entry(), so update that code to use the new function.

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 14 insertions, 29 deletions

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index cc986b824181..c1cf020d1889 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1342,13 +1342,12 @@ static struct buffer_head * ext4_find_entry (struct inode *dir,
 	struct super_block *sb;
 	struct buffer_head *bh_use[NAMEI_RA_SIZE];
 	struct buffer_head *bh, *ret = NULL;
-	ext4_lblk_t start, block, b;
+	ext4_lblk_t start, block;
 	const u8 *name = d_name->name;
-	int ra_max = 0;		/* Number of bh's in the readahead
+	size_t ra_max = 0;	/* Number of bh's in the readahead
 				   buffer, bh_use[] */
-	int ra_ptr = 0;		/* Current index into readahead
+	size_t ra_ptr = 0;	/* Current index into readahead
 				   buffer */
-	int num = 0;
 	ext4_lblk_t  nblocks;
 	int i, namelen, retval;
 	struct ext4_filename fname;
@@ -1411,31 +1410,17 @@ restart:
 		if (ra_ptr >= ra_max) {
 			/* Refill the readahead buffer */
 			ra_ptr = 0;
-			b = block;
-			for (ra_max = 0; ra_max < NAMEI_RA_SIZE; ra_max++) {
-				/*
-				 * Terminate if we reach the end of the
-				 * directory and must wrap, or if our
-				 * search has finished at this block.
-				 */
-				if (b >= nblocks || (num && block == start)) {
-					bh_use[ra_max] = NULL;
-					break;
-				}
-				num++;
-				bh = ext4_getblk(NULL, dir, b++, 0);
-				if (IS_ERR(bh)) {
-					if (ra_max == 0) {
-						ret = bh;
-						goto cleanup_and_exit;
-					}
-					break;
-				}
-				bh_use[ra_max] = bh;
-				if (bh)
-					ll_rw_block(REQ_OP_READ,
-						    REQ_META | REQ_PRIO,
-						    1, &bh);
+			if (block < start)
+				ra_max = start - block;
+			else
+				ra_max = nblocks - block;
+			ra_max = min(ra_max, ARRAY_SIZE(bh_use));
+			retval = ext4_bread_batch(dir, block, ra_max,
+						  false /* wait */, bh_use);
+			if (retval) {
+				ret = ERR_PTR(retval);
+				ra_max = 0;
+				goto cleanup_and_exit;
 			}
 		}
 		if ((bh = bh_use[ra_ptr++]) == NULL)