[Btrfs-devel] fix block readahead in btrfs_next_leaf

[Yan Zheng]

2007/8/27, Chris Mason <chris.mason at oracle.com>:
> It is hard to comment on this patch because there's no description for
> why you think it fixes block readahead.  But, reada_for_search tries to
> cluster blocks close to the one indicated in path->nodes[level][slot],
> so always using slot=zero should make us cluster by the first block
> pointer in the node.
> The defrag code tries to keep the nodes mostly contiguous, but it
> should be better to cluster by the block we're actually looking for.
> -chris
>


int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
{
	int slot;
	int level = 1;
	u64 blocknr;
	struct buffer_head *c;
	struct btrfs_node *c_node;
	struct buffer_head *next = NULL;

	while(level < BTRFS_MAX_LEVEL) {
		if (!path->nodes[level])
			return 1;
		slot = path->slots[level] + 1;
		c = path->nodes[level];
		c_node = btrfs_buffer_node(c);
		if (slot >= btrfs_header_nritems(&c_node->header)) {
			level++;
			continue;
		}
		blocknr = btrfs_node_blockptr(c_node, slot);
		if (next)
			btrfs_block_release(root, next);
		if (path->reada)
			reada_for_search(root, path, level, slot);
		next = read_tree_block(root, blocknr);
		BUG_ON (!next);
		break;
	}
	path->slots[level] = slot;
	while(1) {
		level--;
		c = path->nodes[level];
		btrfs_block_release(root, c);
		path->nodes[level] = next;
		path->slots[level] = 0;
		if (!level)
			break;
		if (path->reada)
			reada_for_search(root, path, level, slot);
		next = read_tree_block(root,
		       btrfs_node_blockptr(btrfs_buffer_node(next), 0));
	}
	return 0;
}

I think in the second while loop,  slot should set to 0.

Regards
YZ