v4.19.13 snapshot.
diff --git a/fs/btrfs/tree-defrag.c b/fs/btrfs/tree-defrag.c
new file mode 100644
index 0000000..3c0987a
--- /dev/null
+++ b/fs/btrfs/tree-defrag.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2007 Oracle. All rights reserved.
+ */
+
+#include <linux/sched.h>
+#include "ctree.h"
+#include "disk-io.h"
+#include "print-tree.h"
+#include "transaction.h"
+#include "locking.h"
+
+/*
+ * Defrag all the leaves in a given btree.
+ * Read all the leaves and try to get key order to
+ * better reflect disk order
+ */
+
+int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
+ struct btrfs_root *root)
+{
+ struct btrfs_path *path = NULL;
+ struct btrfs_key key;
+ int ret = 0;
+ int wret;
+ int level;
+ int next_key_ret = 0;
+ u64 last_ret = 0;
+
+ if (root->fs_info->extent_root == root) {
+ /*
+ * there's recursion here right now in the tree locking,
+ * we can't defrag the extent root without deadlock
+ */
+ goto out;
+ }
+
+ if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
+ goto out;
+
+ path = btrfs_alloc_path();
+ if (!path)
+ return -ENOMEM;
+
+ level = btrfs_header_level(root->node);
+
+ if (level == 0)
+ goto out;
+
+ if (root->defrag_progress.objectid == 0) {
+ struct extent_buffer *root_node;
+ u32 nritems;
+
+ root_node = btrfs_lock_root_node(root);
+ btrfs_set_lock_blocking(root_node);
+ nritems = btrfs_header_nritems(root_node);
+ root->defrag_max.objectid = 0;
+ /* from above we know this is not a leaf */
+ btrfs_node_key_to_cpu(root_node, &root->defrag_max,
+ nritems - 1);
+ btrfs_tree_unlock(root_node);
+ free_extent_buffer(root_node);
+ memset(&key, 0, sizeof(key));
+ } else {
+ memcpy(&key, &root->defrag_progress, sizeof(key));
+ }
+
+ path->keep_locks = 1;
+
+ ret = btrfs_search_forward(root, &key, path, BTRFS_OLDEST_GENERATION);
+ if (ret < 0)
+ goto out;
+ if (ret > 0) {
+ ret = 0;
+ goto out;
+ }
+ btrfs_release_path(path);
+ /*
+ * We don't need a lock on a leaf. btrfs_realloc_node() will lock all
+ * leafs from path->nodes[1], so set lowest_level to 1 to avoid later
+ * a deadlock (attempting to write lock an already write locked leaf).
+ */
+ path->lowest_level = 1;
+ wret = btrfs_search_slot(trans, root, &key, path, 0, 1);
+
+ if (wret < 0) {
+ ret = wret;
+ goto out;
+ }
+ if (!path->nodes[1]) {
+ ret = 0;
+ goto out;
+ }
+ /*
+ * The node at level 1 must always be locked when our path has
+ * keep_locks set and lowest_level is 1, regardless of the value of
+ * path->slots[1].
+ */
+ BUG_ON(path->locks[1] == 0);
+ ret = btrfs_realloc_node(trans, root,
+ path->nodes[1], 0,
+ &last_ret,
+ &root->defrag_progress);
+ if (ret) {
+ WARN_ON(ret == -EAGAIN);
+ goto out;
+ }
+ /*
+ * Now that we reallocated the node we can find the next key. Note that
+ * btrfs_find_next_key() can release our path and do another search
+ * without COWing, this is because even with path->keep_locks = 1,
+ * btrfs_search_slot() / ctree.c:unlock_up() does not keeps a lock on a
+ * node when path->slots[node_level - 1] does not point to the last
+ * item or a slot beyond the last item (ctree.c:unlock_up()). Therefore
+ * we search for the next key after reallocating our node.
+ */
+ path->slots[1] = btrfs_header_nritems(path->nodes[1]);
+ next_key_ret = btrfs_find_next_key(root, path, &key, 1,
+ BTRFS_OLDEST_GENERATION);
+ if (next_key_ret == 0) {
+ memcpy(&root->defrag_progress, &key, sizeof(key));
+ ret = -EAGAIN;
+ }
+out:
+ btrfs_free_path(path);
+ if (ret == -EAGAIN) {
+ if (root->defrag_max.objectid > root->defrag_progress.objectid)
+ goto done;
+ if (root->defrag_max.type > root->defrag_progress.type)
+ goto done;
+ if (root->defrag_max.offset > root->defrag_progress.offset)
+ goto done;
+ ret = 0;
+ }
+done:
+ if (ret != -EAGAIN) {
+ memset(&root->defrag_progress, 0,
+ sizeof(root->defrag_progress));
+ root->defrag_trans_start = trans->transid;
+ }
+ return ret;
+}