[PATCH v2] btrfs: Turn delayed_nodes_tree into an XArray

[Gabriel Niebler <gniebler@suse.com>]

… in the btrfs_root struct. Also adjust all usages of this object to use
the XArray API.

Signed-off-by: Gabriel Niebler <gniebler@suse.com>
---

Notes:
    XArrays offer a somewhat nicer API than radix trees and were implemented
    specifically to replace the latter. They utilize the exact same underlying
    data structure, but their API is notionally easier to use, as it provides
    array semantics to the user of radix trees. The higher level API also
    takes care of locking, adding even more ease of use.
    
    The btrfs code uses radix trees in several places. This patch only
    converts the `delayed_nodes_tree` member of the btrfs_root struct.
    
    It survived a complete fstests run.

 fs/btrfs/ctree.h         |  4 ++--
 fs/btrfs/delayed-inode.c | 48 ++++++++++++++++++----------------------
 fs/btrfs/disk-io.c       |  2 +-
 fs/btrfs/inode.c         |  2 +-
 4 files changed, 26 insertions(+), 30 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index b7631b88426e..9377dded9679 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1224,10 +1224,10 @@ struct btrfs_root {
 	struct rb_root inode_tree;
 
 	/*
-	 * radix tree that keeps track of delayed nodes of every inode,
+	 * XArray that keeps track of delayed nodes of every inode,
 	 * protected by inode_lock
 	 */
-	struct radix_tree_root delayed_nodes_tree;
+	struct xarray delayed_nodes;
 	/*
 	 * right now this just gets used so that a root has its own devid
 	 * for stat.  It may be used for more later
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 748bf6b0d860..89e1c39c2aef 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -78,7 +78,7 @@ static struct btrfs_delayed_node *btrfs_get_delayed_node(
 	}
 
 	spin_lock(&root->inode_lock);
-	node = radix_tree_lookup(&root->delayed_nodes_tree, ino);
+	node = xa_load(&root->delayed_nodes, (unsigned long)ino);
 
 	if (node) {
 		if (btrfs_inode->delayed_node) {
@@ -90,9 +90,9 @@ static struct btrfs_delayed_node *btrfs_get_delayed_node(
 
 		/*
 		 * It's possible that we're racing into the middle of removing
-		 * this node from the radix tree.  In this case, the refcount
+		 * this node from the XArray.  In this case, the refcount
 		 * was zero and it should never go back to one.  Just return
-		 * NULL like it was never in the radix at all; our release
+		 * NULL like it was never in the XArray at all; our release
 		 * function is in the process of removing it.
 		 *
 		 * Some implementations of refcount_inc refuse to bump the
@@ -100,7 +100,7 @@ static struct btrfs_delayed_node *btrfs_get_delayed_node(
 		 * here, refcount_inc() may decide to just WARN_ONCE() instead
 		 * of actually bumping the refcount.
 		 *
-		 * If this node is properly in the radix, we want to bump the
+		 * If this node is properly in the XArray, we want to bump the
 		 * refcount twice, once for the inode and once for this get
 		 * operation.
 		 */
@@ -141,23 +141,17 @@ static struct btrfs_delayed_node *btrfs_get_or_create_delayed_node(
 	/* cached in the btrfs inode and can be accessed */
 	refcount_set(&node->refs, 2);
 
-	ret = radix_tree_preload(GFP_NOFS);
-	if (ret) {
-		kmem_cache_free(delayed_node_cache, node);
-		return ERR_PTR(ret);
-	}
-
 	spin_lock(&root->inode_lock);
-	ret = radix_tree_insert(&root->delayed_nodes_tree, ino, node);
-	if (ret == -EEXIST) {
+	ret = xa_insert(&root->delayed_nodes, ino, node, GFP_NOFS);
+	if (ret) {
 		spin_unlock(&root->inode_lock);
 		kmem_cache_free(delayed_node_cache, node);
-		radix_tree_preload_end();
-		goto again;
+		if (ret == -EBUSY)
+			goto again;
+		return ERR_PTR(ret);
 	}
 	btrfs_inode->delayed_node = node;
 	spin_unlock(&root->inode_lock);
-	radix_tree_preload_end();
 
 	return node;
 }
@@ -276,8 +270,7 @@ static void __btrfs_release_delayed_node(
 		 * back up.  We can delete it now.
 		 */
 		ASSERT(refcount_read(&delayed_node->refs) == 0);
-		radix_tree_delete(&root->delayed_nodes_tree,
-				  delayed_node->inode_id);
+		xa_erase(&root->delayed_nodes, delayed_node->inode_id);
 		spin_unlock(&root->inode_lock);
 		kmem_cache_free(delayed_node_cache, delayed_node);
 	}
@@ -1870,29 +1863,32 @@ void btrfs_kill_delayed_inode_items(struct btrfs_inode *inode)
 
 void btrfs_kill_all_delayed_nodes(struct btrfs_root *root)
 {
-	u64 inode_id = 0;
+	unsigned long index;
+	struct btrfs_delayed_node *delayed_node;
 	struct btrfs_delayed_node *delayed_nodes[8];
 	int i, n;
 
 	while (1) {
 		spin_lock(&root->inode_lock);
-		n = radix_tree_gang_lookup(&root->delayed_nodes_tree,
-					   (void **)delayed_nodes, inode_id,
-					   ARRAY_SIZE(delayed_nodes));
-		if (!n) {
+		if (xa_empty(&root->delayed_nodes)) {
 			spin_unlock(&root->inode_lock);
 			break;
 		}
 
-		inode_id = delayed_nodes[n - 1]->inode_id + 1;
-		for (i = 0; i < n; i++) {
+		n = 0;
+		xa_for_each_start(&root->delayed_nodes, index,
+				  delayed_node, index) {
 			/*
 			 * Don't increase refs in case the node is dead and
 			 * about to be removed from the tree in the loop below
 			 */
-			if (!refcount_inc_not_zero(&delayed_nodes[i]->refs))
-				delayed_nodes[i] = NULL;
+			if (!refcount_inc_not_zero(&delayed_node->refs))
+				delayed_nodes[n] = NULL;
+			n++;
+			if (n >= ARRAY_SIZE(delayed_nodes))
+				break;
 		}
+		index++;
 		spin_unlock(&root->inode_lock);
 
 		for (i = 0; i < n; i++) {
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b30309f187cf..2a49c772d175 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1164,7 +1164,7 @@ static void __setup_root(struct btrfs_root *root, struct btrfs_fs_info *fs_info,
 	root->nr_delalloc_inodes = 0;
 	root->nr_ordered_extents = 0;
 	root->inode_tree = RB_ROOT;
-	INIT_RADIX_TREE(&root->delayed_nodes_tree, GFP_ATOMIC);
+	xa_init_flags(&root->delayed_nodes, GFP_ATOMIC);
 
 	btrfs_init_root_block_rsv(root);
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 17d5557f98ec..5b5355fdfa62 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3827,7 +3827,7 @@ static int btrfs_read_locked_inode(struct inode *inode,
 	 * cache.
 	 *
 	 * This is required for both inode re-read from disk and delayed inode
-	 * in delayed_nodes_tree.
+	 * in the delayed_nodes XArray.
 	 */
 	if (BTRFS_I(inode)->last_trans == fs_info->generation)
 		set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
-- 
2.35.1