Btrfs: don't read leaf blocks containing only checksums during truncate
Checksum items take up a significant portion of the metadata for large files.
It is possible to avoid reading them during truncates by checking the keys in
the higher level nodes.
If a given leaf is followed by another leaf where the lowest key is a checksum
item from the same file, we know we can safely delete the leaf without
reading it.
For a 32GB file on a 6 drive raid0 array, Btrfs needs 8s to delete
the file with a cold cache. It is read bound during the run.
With this change, Btrfs is able to delete the file in 0.5s
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index ff3261f..2eab464 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1388,7 +1388,7 @@
struct btrfs_key prealloc_block;
lowest_level = p->lowest_level;
- WARN_ON(lowest_level && ins_len);
+ WARN_ON(lowest_level && ins_len > 0);
WARN_ON(p->nodes[0] != NULL);
WARN_ON(cow && root == root->fs_info->extent_root &&
!mutex_is_locked(&root->fs_info->alloc_mutex));
@@ -3187,6 +3187,36 @@
}
/*
+ * a helper function to delete the leaf pointed to by path->slots[1] and
+ * path->nodes[1]. bytenr is the node block pointer, but since the callers
+ * already know it, it is faster to have them pass it down than to
+ * read it out of the node again.
+ *
+ * This deletes the pointer in path->nodes[1] and frees the leaf
+ * block extent. zero is returned if it all worked out, < 0 otherwise.
+ *
+ * The path must have already been setup for deleting the leaf, including
+ * all the proper balancing. path->nodes[1] must be locked.
+ */
+noinline int btrfs_del_leaf(struct btrfs_trans_handle *trans,
+ struct btrfs_root *root,
+ struct btrfs_path *path, u64 bytenr)
+{
+ int ret;
+ u64 root_gen = btrfs_header_generation(path->nodes[1]);
+
+ ret = del_ptr(trans, root, path, 1, path->slots[1]);
+ if (ret)
+ return ret;
+
+ ret = btrfs_free_extent(trans, root, bytenr,
+ btrfs_level_size(root, 0),
+ path->nodes[1]->start,
+ btrfs_header_owner(path->nodes[1]),
+ root_gen, 0, 0, 1);
+ return ret;
+}
+/*
* delete the item at the leaf level in path. If that empties
* the leaf, remove it from the tree
*/
@@ -3251,17 +3281,8 @@
if (leaf == root->node) {
btrfs_set_header_level(leaf, 0);
} else {
- u64 root_gen = btrfs_header_generation(path->nodes[1]);
- wret = del_ptr(trans, root, path, 1, path->slots[1]);
- if (wret)
- ret = wret;
- wret = btrfs_free_extent(trans, root,
- leaf->start, leaf->len,
- path->nodes[1]->start,
- btrfs_header_owner(path->nodes[1]),
- root_gen, 0, 0, 1);
- if (wret)
- ret = wret;
+ ret = btrfs_del_leaf(trans, root, path, leaf->start);
+ BUG_ON(ret);
}
} else {
int used = leaf_space_used(leaf, 0, nritems);
@@ -3296,24 +3317,10 @@
}
if (btrfs_header_nritems(leaf) == 0) {
- u64 root_gen;
- u64 bytenr = leaf->start;
- u32 blocksize = leaf->len;
-
- root_gen = btrfs_header_generation(
- path->nodes[1]);
-
- wret = del_ptr(trans, root, path, 1, slot);
- if (wret)
- ret = wret;
-
+ path->slots[1] = slot;
+ ret = btrfs_del_leaf(trans, root, path, leaf->start);
+ BUG_ON(ret);
free_extent_buffer(leaf);
- wret = btrfs_free_extent(trans, root, bytenr,
- blocksize, path->nodes[1]->start,
- btrfs_header_owner(path->nodes[1]),
- root_gen, 0, 0, 1);
- if (wret)
- ret = wret;
} else {
/* if we're still in the path, make sure
* we're dirty. Otherwise, one of the
@@ -3418,8 +3425,8 @@
level = btrfs_header_level(cur);
sret = bin_search(cur, min_key, level, &slot);
- /* at level = 0, we're done, setup the path and exit */
- if (level == 0) {
+ /* at the lowest level, we're done, setup the path and exit */
+ if (level == path->lowest_level) {
if (slot >= nritems)
goto find_next_key;
ret = 0;