Btrfs: Fix snapshot deletion to release the alloc_mutex much more often.
This lowers the impact of snapshot deletion on the rest of the FS.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 544fc3f..6274f30 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1223,8 +1223,8 @@
ret = btrfs_make_block_group(trans, extent_root, 0, flags,
BTRFS_FIRST_CHUNK_TREE_OBJECTID, start, num_bytes);
BUG_ON(ret);
- mutex_unlock(&extent_root->fs_info->chunk_mutex);
out:
+ mutex_unlock(&extent_root->fs_info->chunk_mutex);
return 0;
}
@@ -2181,18 +2181,30 @@
continue;
}
}
- mutex_unlock(&root->fs_info->alloc_mutex);
ret = readahead_tree_block(root, bytenr, blocksize,
btrfs_node_ptr_generation(node, i));
last = bytenr + blocksize;
cond_resched();
- mutex_lock(&root->fs_info->alloc_mutex);
if (ret)
break;
}
}
/*
+ * we want to avoid as much random IO as we can with the alloc mutex
+ * held, so drop the lock and do the lookup, then do it again with the
+ * lock held.
+ */
+int drop_snap_lookup_refcount(struct btrfs_root *root, u64 start, u64 len,
+ u32 *refs)
+{
+ mutex_unlock(&root->fs_info->alloc_mutex);
+ lookup_extent_ref(NULL, root, start, len, refs);
+ mutex_lock(&root->fs_info->alloc_mutex);
+ return lookup_extent_ref(NULL, root, start, len, refs);
+}
+
+/*
* helper function for drop_snapshot, this walks down the tree dropping ref
* counts as it goes.
*/
@@ -2215,8 +2227,7 @@
WARN_ON(*level < 0);
WARN_ON(*level >= BTRFS_MAX_LEVEL);
- ret = lookup_extent_ref(trans, root,
- path->nodes[*level]->start,
+ ret = drop_snap_lookup_refcount(root, path->nodes[*level]->start,
path->nodes[*level]->len, &refs);
BUG_ON(ret);
if (refs > 1)
@@ -2245,7 +2256,7 @@
ptr_gen = btrfs_node_ptr_generation(cur, path->slots[*level]);
blocksize = btrfs_level_size(root, *level - 1);
- ret = lookup_extent_ref(trans, root, bytenr, blocksize, &refs);
+ ret = drop_snap_lookup_refcount(root, bytenr, blocksize, &refs);
BUG_ON(ret);
if (refs != 1) {
parent = path->nodes[*level];
@@ -2261,15 +2272,16 @@
next = btrfs_find_tree_block(root, bytenr, blocksize);
if (!next || !btrfs_buffer_uptodate(next, ptr_gen)) {
free_extent_buffer(next);
+ mutex_unlock(&root->fs_info->alloc_mutex);
+
reada_walk_down(root, cur, path->slots[*level]);
- mutex_unlock(&root->fs_info->alloc_mutex);
next = read_tree_block(root, bytenr, blocksize,
ptr_gen);
mutex_lock(&root->fs_info->alloc_mutex);
/* we've dropped the lock, double check */
- ret = lookup_extent_ref(trans, root, bytenr,
+ ret = drop_snap_lookup_refcount(root, bytenr,
blocksize, &refs);
BUG_ON(ret);
if (refs != 1) {