ext4: collapse a single extent tree block into the inode if possible
If an inode has more than 4 extents, but then later some of the
extents are merged together, we can optimize the file system by moving
the extents up into the inode, and discarding the extent tree block.
This is important, because if there are a large number of inodes with
an external extent tree blocks where the contents could fit in the
inode, this can significantly increase the fsck time of the file
system.
Google-Bug-Id: 6801242
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index aabbb3f..e8755c2 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1656,16 +1656,60 @@
}
/*
+ * This function does a very simple check to see if we can collapse
+ * an extent tree with a single extent tree leaf block into the inode.
+ */
+static void ext4_ext_try_to_merge_up(handle_t *handle,
+ struct inode *inode,
+ struct ext4_ext_path *path)
+{
+ size_t s;
+ unsigned max_root = ext4_ext_space_root(inode, 0);
+ ext4_fsblk_t blk;
+
+ if ((path[0].p_depth != 1) ||
+ (le16_to_cpu(path[0].p_hdr->eh_entries) != 1) ||
+ (le16_to_cpu(path[1].p_hdr->eh_entries) > max_root))
+ return;
+
+ /*
+ * We need to modify the block allocation bitmap and the block
+ * group descriptor to release the extent tree block. If we
+ * can't get the journal credits, give up.
+ */
+ if (ext4_journal_extend(handle, 2))
+ return;
+
+ /*
+ * Copy the extent data up to the inode
+ */
+ blk = ext4_idx_pblock(path[0].p_idx);
+ s = le16_to_cpu(path[1].p_hdr->eh_entries) *
+ sizeof(struct ext4_extent_idx);
+ s += sizeof(struct ext4_extent_header);
+
+ memcpy(path[0].p_hdr, path[1].p_hdr, s);
+ path[0].p_depth = 0;
+ path[0].p_ext = EXT_FIRST_EXTENT(path[0].p_hdr) +
+ (path[1].p_ext - EXT_FIRST_EXTENT(path[1].p_hdr));
+ path[0].p_hdr->eh_max = cpu_to_le16(max_root);
+
+ brelse(path[1].p_bh);
+ ext4_free_blocks(handle, inode, NULL, blk, 1,
+ EXT4_FREE_BLOCKS_METADATA | EXT4_FREE_BLOCKS_FORGET);
+}
+
+/*
* This function tries to merge the @ex extent to neighbours in the tree.
* return 1 if merge left else 0.
*/
-static int ext4_ext_try_to_merge(struct inode *inode,
+static void ext4_ext_try_to_merge(handle_t *handle,
+ struct inode *inode,
struct ext4_ext_path *path,
struct ext4_extent *ex) {
struct ext4_extent_header *eh;
unsigned int depth;
int merge_done = 0;
- int ret = 0;
depth = ext_depth(inode);
BUG_ON(path[depth].p_hdr == NULL);
@@ -1675,9 +1719,9 @@
merge_done = ext4_ext_try_to_merge_right(inode, path, ex - 1);
if (!merge_done)
- ret = ext4_ext_try_to_merge_right(inode, path, ex);
+ (void) ext4_ext_try_to_merge_right(inode, path, ex);
- return ret;
+ ext4_ext_try_to_merge_up(handle, inode, path);
}
/*
@@ -1893,7 +1937,7 @@
merge:
/* try to merge extents */
if (!(flag & EXT4_GET_BLOCKS_PRE_IO))
- ext4_ext_try_to_merge(inode, path, nearex);
+ ext4_ext_try_to_merge(handle, inode, path, nearex);
/* time to correct all indexes above */
@@ -1901,7 +1945,7 @@
if (err)
goto cleanup;
- err = ext4_ext_dirty(handle, inode, path + depth);
+ err = ext4_ext_dirty(handle, inode, path + path->p_depth);
cleanup:
if (npath) {
@@ -2924,9 +2968,9 @@
ext4_ext_mark_initialized(ex);
if (!(flags & EXT4_GET_BLOCKS_PRE_IO))
- ext4_ext_try_to_merge(inode, path, ex);
+ ext4_ext_try_to_merge(handle, inode, path, ex);
- err = ext4_ext_dirty(handle, inode, path + depth);
+ err = ext4_ext_dirty(handle, inode, path + path->p_depth);
goto out;
}
@@ -2958,8 +3002,8 @@
goto fix_extent_len;
/* update the extent length and mark as initialized */
ex->ee_len = cpu_to_le16(ee_len);
- ext4_ext_try_to_merge(inode, path, ex);
- err = ext4_ext_dirty(handle, inode, path + depth);
+ ext4_ext_try_to_merge(handle, inode, path, ex);
+ err = ext4_ext_dirty(handle, inode, path + path->p_depth);
goto out;
} else if (err)
goto fix_extent_len;
@@ -3191,8 +3235,8 @@
if (err)
goto out;
ext4_ext_mark_initialized(ex);
- ext4_ext_try_to_merge(inode, path, ex);
- err = ext4_ext_dirty(handle, inode, path + depth);
+ ext4_ext_try_to_merge(handle, inode, path, ex);
+ err = ext4_ext_dirty(handle, inode, path + path->p_depth);
goto out;
}
@@ -3333,10 +3377,10 @@
/* note: ext4_ext_correct_indexes() isn't needed here because
* borders are not changed
*/
- ext4_ext_try_to_merge(inode, path, ex);
+ ext4_ext_try_to_merge(handle, inode, path, ex);
/* Mark modified extent as dirty */
- err = ext4_ext_dirty(handle, inode, path + depth);
+ err = ext4_ext_dirty(handle, inode, path + path->p_depth);
out:
ext4_ext_show_leaf(inode, path);
return err;