This patch optimize the backrefs update part of btrfs_drop_snapshot. It avoids reading level 0 tree blocks that already use full backrefs. Signed-off-by: Yan Zheng <zheng.yan@oracle.com> --- diff -urp 1/fs/btrfs/extent-tree.c 2/fs/btrfs/extent-tree.c --- 1/fs/btrfs/extent-tree.c 2009-10-09 09:38:36.357269710 +0800 +++ 2/fs/btrfs/extent-tree.c 2009-10-09 11:09:16.828020537 +0800 @@ -4809,6 +4809,7 @@ static noinline void reada_walk_down(str u64 bytenr; u64 generation; u64 refs; + u64 flags; u64 last = 0; u32 nritems; u32 blocksize; @@ -4846,15 +4847,19 @@ static noinline void reada_walk_down(str generation <= root->root_key.offset) continue; + /* We don''t lock the tree block, it''s OK to be racy here */ + ret = btrfs_lookup_extent_info(trans, root, bytenr, blocksize, + &refs, &flags); + BUG_ON(ret); + BUG_ON(refs == 0); + if (wc->stage == DROP_REFERENCE) { - ret = btrfs_lookup_extent_info(trans, root, - bytenr, blocksize, - &refs, NULL); - BUG_ON(ret); - BUG_ON(refs == 0); if (refs == 1) goto reada; + if (wc->level == 1 && + (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF)) + continue; if (!wc->update_ref || generation <= root->root_key.offset) continue; @@ -4863,6 +4868,10 @@ static noinline void reada_walk_down(str &wc->update_progress); if (ret < 0) continue; + } else { + if (wc->level == 1 && + (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF)) + continue; } reada: ret = readahead_tree_block(root, bytenr, blocksize, @@ -4886,7 +4895,7 @@ reada: static noinline int walk_down_proc(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct btrfs_path *path, - struct walk_control *wc) + struct walk_control *wc, int lookup_info) { int level = wc->level; struct extent_buffer *eb = path->nodes[level]; @@ -4901,8 +4910,9 @@ static noinline int walk_down_proc(struc * when reference count of tree block is 1, it won''t increase * again. once full backref flag is set, we never clear it. */ - if ((wc->stage == DROP_REFERENCE && wc->refs[level] != 1) || - (wc->stage == UPDATE_BACKREF && !(wc->flags[level] & flag))) { + if (lookup_info && + ((wc->stage == DROP_REFERENCE && wc->refs[level] != 1) || + (wc->stage == UPDATE_BACKREF && !(wc->flags[level] & flag)))) { BUG_ON(!path->locks[level]); ret = btrfs_lookup_extent_info(trans, root, eb->start, eb->len, @@ -4963,7 +4973,7 @@ static noinline int walk_down_proc(struc static noinline int do_walk_down(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct btrfs_path *path, - struct walk_control *wc) + struct walk_control *wc, int *lookup_info) { u64 bytenr; u64 generation; @@ -4983,8 +4993,10 @@ static noinline int do_walk_down(struct * for the subtree */ if (wc->stage == UPDATE_BACKREF && - generation <= root->root_key.offset) + generation <= root->root_key.offset) { + *lookup_info = 1; return 1; + } bytenr = btrfs_node_blockptr(path->nodes[level], path->slots[level]); blocksize = btrfs_level_size(root, level - 1); @@ -4997,14 +5009,19 @@ static noinline int do_walk_down(struct btrfs_tree_lock(next); btrfs_set_lock_blocking(next); - if (wc->stage == DROP_REFERENCE) { - ret = btrfs_lookup_extent_info(trans, root, bytenr, blocksize, - &wc->refs[level - 1], - &wc->flags[level - 1]); - BUG_ON(ret); - BUG_ON(wc->refs[level - 1] == 0); + ret = btrfs_lookup_extent_info(trans, root, bytenr, blocksize, + &wc->refs[level - 1], + &wc->flags[level - 1]); + BUG_ON(ret); + BUG_ON(wc->refs[level - 1] == 0); + *lookup_info = 0; + if (wc->stage == DROP_REFERENCE) { if (wc->refs[level - 1] > 1) { + if (level == 1 && + (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF)) + goto skip; + if (!wc->update_ref || generation <= root->root_key.offset) goto skip; @@ -5018,12 +5035,17 @@ static noinline int do_walk_down(struct wc->stage = UPDATE_BACKREF; wc->shared_level = level - 1; } + } else { + if (level == 1 && + (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF)) + goto skip; } if (!btrfs_buffer_uptodate(next, generation)) { btrfs_tree_unlock(next); free_extent_buffer(next); next = NULL; + *lookup_info = 1; } if (!next) { @@ -5046,21 +5068,22 @@ static noinline int do_walk_down(struct skip: wc->refs[level - 1] = 0; wc->flags[level - 1] = 0; + if (wc->stage == DROP_REFERENCE) { + if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF) { + parent = path->nodes[level]->start; + } else { + BUG_ON(root->root_key.objectid !+ btrfs_header_owner(path->nodes[level])); + parent = 0; + } - if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF) { - parent = path->nodes[level]->start; - } else { - BUG_ON(root->root_key.objectid !- btrfs_header_owner(path->nodes[level])); - parent = 0; + ret = btrfs_free_extent(trans, root, bytenr, blocksize, parent, + root->root_key.objectid, level - 1, 0); + BUG_ON(ret); } - - ret = btrfs_free_extent(trans, root, bytenr, blocksize, parent, - root->root_key.objectid, level - 1, 0); - BUG_ON(ret); - btrfs_tree_unlock(next); free_extent_buffer(next); + *lookup_info = 1; return 1; } @@ -5174,6 +5197,7 @@ static noinline int walk_down_tree(struc struct walk_control *wc) { int level = wc->level; + int lookup_info = 1; int ret; while (level >= 0) { @@ -5181,14 +5205,14 @@ static noinline int walk_down_tree(struc btrfs_header_nritems(path->nodes[level])) break; - ret = walk_down_proc(trans, root, path, wc); + ret = walk_down_proc(trans, root, path, wc, lookup_info); if (ret > 0) break; if (level == 0) break; - ret = do_walk_down(trans, root, path, wc); + ret = do_walk_down(trans, root, path, wc, &lookup_info); if (ret > 0) { path->slots[level]++; continue; -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html