btrfs: cleanup extent buffer readahead

We're going to pass around more information when we allocate extent
buffers, in order to make that cleaner how we do readahead.  Most of the
callers have the parent node that we're getting our blockptr from, with
the sole exception of relocation which simply has the bytenr it wants to
read.

Add a helper that takes the current arguments that we need (bytenr and
gen), and add another helper for simply reading the slot out of a node.
In followup patches the helper that takes all the extra arguments will
be expanded, and the simpler helper won't need to have it's arguments
adjusted.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.c

@@ -2226,7 +2226,7 @@ static void reada_for_search(struct btrfs_fs_info *fs_info,
 		search = btrfs_node_blockptr(node, nr);
 		if ((search <= target && target - search <= 65536) ||
 		    (search > target && search - target <= 65536)) {
-			readahead_tree_block(fs_info, search);
+			btrfs_readahead_node_child(node, nr);
 			nread += blocksize;
 		}
 		nscan++;
@@ -2235,16 +2235,11 @@ static void reada_for_search(struct btrfs_fs_info *fs_info,
 	}
 }
 
-static noinline void reada_for_balance(struct btrfs_fs_info *fs_info,
-				       struct btrfs_path *path, int level)
+static noinline void reada_for_balance(struct btrfs_path *path, int level)
 {
+	struct extent_buffer *parent;
 	int slot;
 	int nritems;
-	struct extent_buffer *parent;
-	struct extent_buffer *eb;
-	u64 gen;
-	u64 block1 = 0;
-	u64 block2 = 0;
 
 	parent = path->nodes[level + 1];
 	if (!parent)
@@ -2253,32 +2248,10 @@ static noinline void reada_for_balance(struct btrfs_fs_info *fs_info,
 	nritems = btrfs_header_nritems(parent);
 	slot = path->slots[level + 1];
 
-	if (slot > 0) {
-		block1 = btrfs_node_blockptr(parent, slot - 1);
-		gen = btrfs_node_ptr_generation(parent, slot - 1);
-		eb = find_extent_buffer(fs_info, block1);
-		/*
-		 * if we get -eagain from btrfs_buffer_uptodate, we
-		 * don't want to return eagain here.  That will loop
-		 * forever
-		 */
-		if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
-			block1 = 0;
-		free_extent_buffer(eb);
-	}
-	if (slot + 1 < nritems) {
-		block2 = btrfs_node_blockptr(parent, slot + 1);
-		gen = btrfs_node_ptr_generation(parent, slot + 1);
-		eb = find_extent_buffer(fs_info, block2);
-		if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
-			block2 = 0;
-		free_extent_buffer(eb);
-	}
-
-	if (block1)
-		readahead_tree_block(fs_info, block1);
-	if (block2)
-		readahead_tree_block(fs_info, block2);
+	if (slot > 0)
+		btrfs_readahead_node_child(parent, slot - 1);
+	if (slot + 1 < nritems)
+		btrfs_readahead_node_child(parent, slot + 1);
 }
 
 
@@ -2454,7 +2427,7 @@ setup_nodes_for_search(struct btrfs_trans_handle *trans,
 			goto again;
 		}
 
-		reada_for_balance(fs_info, p, level);
+		reada_for_balance(p, level);
 		sret = split_node(trans, root, p, level);
 
 		BUG_ON(sret > 0);
@@ -2473,7 +2446,7 @@ setup_nodes_for_search(struct btrfs_trans_handle *trans,
 			goto again;
 		}
 
-		reada_for_balance(fs_info, p, level);
+		reada_for_balance(p, level);
 		sret = balance_level(trans, root, p, level);
 
 		if (sret) {

fs/btrfs/disk-io.c

@@ -953,22 +953,6 @@ static const struct address_space_operations btree_aops = {
 	.set_page_dirty = btree_set_page_dirty,
 };
 
-void readahead_tree_block(struct btrfs_fs_info *fs_info, u64 bytenr)
-{
-	struct extent_buffer *buf = NULL;
-	int ret;
-
-	buf = btrfs_find_create_tree_block(fs_info, bytenr);
-	if (IS_ERR(buf))
-		return;
-
-	ret = read_extent_buffer_pages(buf, WAIT_NONE, 0);
-	if (ret < 0)
-		free_extent_buffer_stale(buf);
-	else
-		free_extent_buffer(buf);
-}
-
 struct extent_buffer *btrfs_find_create_tree_block(
 						struct btrfs_fs_info *fs_info,
 						u64 bytenr)

fs/btrfs/disk-io.h

@@ -45,7 +45,6 @@ int btrfs_verify_level_key(struct extent_buffer *eb, int level,
 struct extent_buffer *read_tree_block(struct btrfs_fs_info *fs_info, u64 bytenr,
 				      u64 parent_transid, int level,
 				      struct btrfs_key *first_key);
-void readahead_tree_block(struct btrfs_fs_info *fs_info, u64 bytenr);
 struct extent_buffer *btrfs_find_create_tree_block(
 						struct btrfs_fs_info *fs_info,
 						u64 bytenr);

fs/btrfs/extent-tree.c

@@ -4859,7 +4859,7 @@ static noinline void reada_walk_down(struct btrfs_trans_handle *trans,
 				continue;
 		}
 reada:
-		readahead_tree_block(fs_info, bytenr);
+		btrfs_readahead_node_child(eb, slot);
 		nread++;
 	}
 	wc->reada_slot = slot;

fs/btrfs/extent_io.c

@@ -6123,3 +6123,50 @@ int try_release_extent_buffer(struct page *page)
 
 	return release_extent_buffer(eb);
 }
+
+/*
+ * btrfs_readahead_tree_block - attempt to readahead a child block
+ * @fs_info:	the fs_info
+ * @bytenr:	bytenr to read
+ * @gen:	generation for the uptodate check, can be 0
+ *
+ * Attempt to readahead a tree block at @bytenr.  If @gen is 0 then we do a
+ * normal uptodate check of the eb, without checking the generation.  If we have
+ * to read the block we will not block on anything.
+ */
+void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
+				u64 bytenr, u64 gen)
+{
+	struct extent_buffer *eb;
+	int ret;
+
+	eb = btrfs_find_create_tree_block(fs_info, bytenr);
+	if (IS_ERR(eb))
+		return;
+
+	if (btrfs_buffer_uptodate(eb, gen, 1)) {
+		free_extent_buffer(eb);
+		return;
+	}
+
+	ret = read_extent_buffer_pages(eb, WAIT_NONE, 0);
+	if (ret < 0)
+		free_extent_buffer_stale(eb);
+	else
+		free_extent_buffer(eb);
+}
+
+/*
+ * btrfs_readahead_node_child - readahead a node's child block
+ * @node:	parent node we're reading from
+ * @slot:	slot in the parent node for the child we want to read
+ *
+ * A helper for btrfs_readahead_tree_block, we simply read the bytenr pointed at
+ * the slot in the node provided.
+ */
+void btrfs_readahead_node_child(struct extent_buffer *node, int slot)
+{
+	btrfs_readahead_tree_block(node->fs_info,
+				   btrfs_node_blockptr(node, slot),
+				   btrfs_node_ptr_generation(node, slot));
+}

fs/btrfs/extent_io.h

@@ -198,6 +198,9 @@ void free_extent_buffer_stale(struct extent_buffer *eb);
 int read_extent_buffer_pages(struct extent_buffer *eb, int wait,
 			     int mirror_num);
 void wait_on_extent_buffer_writeback(struct extent_buffer *eb);
+void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
+				u64 bytenr, u64 gen);
+void btrfs_readahead_node_child(struct extent_buffer *node, int slot);
 
 static inline int num_extent_pages(const struct extent_buffer *eb)
 {

fs/btrfs/relocation.c

@@ -2542,7 +2542,7 @@ int relocate_tree_blocks(struct btrfs_trans_handle *trans,
 	/* Kick in readahead for tree blocks with missing keys */
 	rbtree_postorder_for_each_entry_safe(block, next, blocks, rb_node) {
 		if (!block->key_ready)
-			readahead_tree_block(fs_info, block->bytenr);
+			btrfs_readahead_tree_block(fs_info, block->bytenr, 0);
 	}
 
 	/* Get first keys */

fs/btrfs/volumes.c

@@ -7071,12 +7071,8 @@ static void readahead_tree_node_children(struct extent_buffer *node)
 	int i;
 	const int nr_items = btrfs_header_nritems(node);
 
-	for (i = 0; i < nr_items; i++) {
-		u64 start;
-
-		start = btrfs_node_blockptr(node, i);
-		readahead_tree_block(node->fs_info, start);
-	}
+	for (i = 0; i < nr_items; i++)
+		btrfs_readahead_node_child(node, i);
 }
 
 int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info)