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>

4 files changed, 92 insertions, 48 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index d50229e92c55..a2bb7d2870e4 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2461,6 +2461,8 @@ extern void ext4_process_freed_data(struct super_block *sb, tid_t commit_tid);
 int ext4_inode_is_fast_symlink(struct inode *inode);
 struct buffer_head *ext4_getblk(handle_t *, struct inode *, ext4_lblk_t, int);
 struct buffer_head *ext4_bread(handle_t *, struct inode *, ext4_lblk_t, int);
+int ext4_bread_batch(struct inode *inode, ext4_lblk_t block, int bh_count,
+                     bool wait, struct buffer_head **bhs);
 int ext4_get_block_unwritten(struct inode *inode, sector_t iblock,
                              struct buffer_head *bh_result, int create);
 int ext4_get_block(struct inode *inode, sector_t iblock,
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 2e6c02258ee2..56bca45bcdf4 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1015,6 +1015,50 @@ struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
         return ERR_PTR(-EIO);
 }
 
+/* Read a contiguous batch of blocks. */
+int ext4_bread_batch(struct inode *inode, ext4_lblk_t block, int bh_count,
+                     bool wait, struct buffer_head **bhs)
+{
+        int i, err;
+
+        for (i = 0; i < bh_count; i++) {
+                bhs[i] = ext4_getblk(NULL, inode, block + i, 0 /* map_flags */);
+                if (IS_ERR(bhs[i])) {
+                        err = PTR_ERR(bhs[i]);
+                        bh_count = i;
+                        goto out_brelse;
+                }
+        }
+
+        for (i = 0; i < bh_count; i++)
+                /* Note that NULL bhs[i] is valid because of holes. */
+                if (bhs[i] && !buffer_uptodate(bhs[i]))
+                        ll_rw_block(REQ_OP_READ, REQ_META | REQ_PRIO, 1,
+                                    &bhs[i]);
+
+        if (!wait)
+                return 0;
+
+        for (i = 0; i < bh_count; i++)
+                if (bhs[i])
+                        wait_on_buffer(bhs[i]);
+
+        for (i = 0; i < bh_count; i++) {
+                if (bhs[i] && !buffer_uptodate(bhs[i])) {
+                        err = -EIO;
+                        goto out_brelse;
+                }
+        }
+        return 0;
+
+out_brelse:
+        for (i = 0; i < bh_count; i++) {
+                brelse(bhs[i]);
+                bhs[i] = NULL;
+        }
+        return err;
+}
+
 int ext4_walk_page_buffers(handle_t *handle,
                            struct buffer_head *head,
                            unsigned from,
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)
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 4025666c5991..5fa912e5d2a6 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -317,28 +317,41 @@ static void ext4_xattr_inode_set_hash(struct inode *ea_inode, u32 hash)
  */
 static int ext4_xattr_inode_read(struct inode *ea_inode, void *buf, size_t size)
 {
-        unsigned long block = 0;
-        struct buffer_head *bh;
-        int blocksize = ea_inode->i_sb->s_blocksize;
-        size_t csize, copied = 0;
-        void *copy_pos = buf;
-
-        while (copied < size) {
-                csize = (size - copied) > blocksize ? blocksize : size - copied;
-                bh = ext4_bread(NULL, ea_inode, block, 0);
-                if (IS_ERR(bh))
-                        return PTR_ERR(bh);
-                if (!bh)
-                        return -EFSCORRUPTED;
+        int blocksize = 1 << ea_inode->i_blkbits;
+        int bh_count = (size + blocksize - 1) >> ea_inode->i_blkbits;
+        int tail_size = (size % blocksize) ?: blocksize;
+        struct buffer_head *bhs_inline[8];
+        struct buffer_head **bhs = bhs_inline;
+        int i, ret;
+
+        if (bh_count > ARRAY_SIZE(bhs_inline)) {
+                bhs = kmalloc_array(bh_count, sizeof(*bhs), GFP_NOFS);
+                if (!bhs)
+                        return -ENOMEM;
+        }
 
-                memcpy(copy_pos, bh->b_data, csize);
-                brelse(bh);
+        ret = ext4_bread_batch(ea_inode, 0 /* block */, bh_count,
+                               true /* wait */, bhs);
+        if (ret)
+                goto free_bhs;
 
-                copy_pos += csize;
-                block += 1;
-                copied += csize;
+        for (i = 0; i < bh_count; i++) {
+                /* There shouldn't be any holes in ea_inode. */
+                if (!bhs[i]) {
+                        ret = -EFSCORRUPTED;
+                        goto put_bhs;
+                }
+                memcpy((char *)buf + blocksize * i, bhs[i]->b_data,
+                       i < bh_count - 1 ? blocksize : tail_size);
         }
-        return 0;
+        ret = 0;
+put_bhs:
+        for (i = 0; i < bh_count; i++)
+                brelse(bhs[i]);
+free_bhs:
+        if (bhs != bhs_inline)
+                kfree(bhs);
+        return ret;
 }
 
 static int ext4_xattr_inode_iget(struct inode *parent, unsigned long ea_ino,