Btrfs: Mixed back reference (FORWARD ROLLING FORMAT CHANGE)

This commit introduces a new kind of back reference for btrfs metadata.
Once a filesystem has been mounted with this commit, IT WILL NO LONGER
BE MOUNTABLE BY OLDER KERNELS.

When a tree block in subvolume tree is cow'd, the reference counts of all
extents it points to are increased by one.  At transaction commit time,
the old root of the subvolume is recorded in a "dead root" data structure,
and the btree it points to is later walked, dropping reference counts
and freeing any blocks where the reference count goes to 0.

The increments done during cow and decrements done after commit cancel out,
and the walk is a very expensive way to go about freeing the blocks that
are no longer referenced by the new btree root.  This commit reduces the
transaction overhead by avoiding the need for dead root records.

When a non-shared tree block is cow'd, we free the old block at once, and the
new block inherits old block's references. When a tree block with reference
count > 1 is cow'd, we increase the reference counts of all extents
the new block points to by one, and decrease the old block's reference count by
one.

This dead tree avoidance code removes the need to modify the reference
counts of lower level extents when a non-shared tree block is cow'd.
But we still need to update back ref for all pointers in the block.
This is because the location of the block is recorded in the back ref
item.

We can solve this by introducing a new type of back ref. The new
back ref provides information about pointer's key, level and in which
tree the pointer lives. This information allow us to find the pointer
by searching the tree. The shortcoming of the new back ref is that it
only works for pointers in tree blocks referenced by their owner trees.

This is mostly a problem for snapshots, where resolving one of these
fuzzy back references would be O(number_of_snapshots) and quite slow.
The solution used here is to use the fuzzy back references in the common
case where a given tree block is only referenced by one root,
and use the full back references when multiple roots have a reference
on a given block.

This commit adds per subvolume red-black tree to keep trace of cached
inodes. The red-black tree helps the balancing code to find cached
inodes whose inode numbers within a given range.

This commit improves the balancing code by introducing several data
structures to keep the state of balancing. The most important one
is the back ref cache. It caches how the upper level tree blocks are
referenced. This greatly reduce the overhead of checking back ref.

The improved balancing code scales significantly better with a large
number of snapshots.

This is a very large commit and was written in a number of
pieces.  But, they depend heavily on the disk format change and were
squashed together to make sure git bisect didn't end up in a
bad state wrt space balancing or the format change.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 139 insertions, 271 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 01b143605ec1..2e177d7f4bb9 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -25,7 +25,6 @@
 #include "disk-io.h"
 #include "transaction.h"
 #include "locking.h"
-#include "ref-cache.h"
 #include "tree-log.h"
 
 #define BTRFS_ROOT_TRANS_TAG 0
@@ -94,45 +93,37 @@ static noinline int join_transaction(struct btrfs_root *root)
  * to make sure the old root from before we joined the transaction is deleted
  * when the transaction commits
  */
-noinline int btrfs_record_root_in_trans(struct btrfs_root *root)
+static noinline int record_root_in_trans(struct btrfs_trans_handle *trans,
+                                         struct btrfs_root *root)
 {
-        struct btrfs_dirty_root *dirty;
-        u64 running_trans_id = root->fs_info->running_transaction->transid;
-        if (root->ref_cows && root->last_trans < running_trans_id) {
+        if (root->ref_cows && root->last_trans < trans->transid) {
                 WARN_ON(root == root->fs_info->extent_root);
-                if (root->root_item.refs != 0) {
-                        radix_tree_tag_set(&root->fs_info->fs_roots_radix,
-                                   (unsigned long)root->root_key.objectid,
-                                   BTRFS_ROOT_TRANS_TAG);
-
-                        dirty = kmalloc(sizeof(*dirty), GFP_NOFS);
-                        BUG_ON(!dirty);
-                        dirty->root = kmalloc(sizeof(*dirty->root), GFP_NOFS);
-                        BUG_ON(!dirty->root);
-                        dirty->latest_root = root;
-                        INIT_LIST_HEAD(&dirty->list);
-
-                        root->commit_root = btrfs_root_node(root);
-
-                        memcpy(dirty->root, root, sizeof(*root));
-                        spin_lock_init(&dirty->root->node_lock);
-                        spin_lock_init(&dirty->root->list_lock);
-                        mutex_init(&dirty->root->objectid_mutex);
-                        mutex_init(&dirty->root->log_mutex);
-                        INIT_LIST_HEAD(&dirty->root->dead_list);
-                        dirty->root->node = root->commit_root;
-                        dirty->root->commit_root = NULL;
+                WARN_ON(root->root_item.refs == 0);
+                WARN_ON(root->commit_root != root->node);
+
+                radix_tree_tag_set(&root->fs_info->fs_roots_radix,
+                           (unsigned long)root->root_key.objectid,
+                           BTRFS_ROOT_TRANS_TAG);
+                root->last_trans = trans->transid;
+                btrfs_init_reloc_root(trans, root);
+        }
+        return 0;
+}
 
-                        spin_lock(&root->list_lock);
-                        list_add(&dirty->root->dead_list, &root->dead_list);
-                        spin_unlock(&root->list_lock);
+int btrfs_record_root_in_trans(struct btrfs_trans_handle *trans,
+                               struct btrfs_root *root)
+{
+        if (!root->ref_cows)
+                return 0;
 
-                        root->dirty_root = dirty;
-                } else {
-                        WARN_ON(1);
-                }
-                root->last_trans = running_trans_id;
+        mutex_lock(&root->fs_info->trans_mutex);
+        if (root->last_trans == trans->transid) {
+                mutex_unlock(&root->fs_info->trans_mutex);
+                return 0;
         }
+
+        record_root_in_trans(trans, root);
+        mutex_unlock(&root->fs_info->trans_mutex);
         return 0;
 }
 
@@ -181,7 +172,6 @@ static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
         ret = join_transaction(root);
         BUG_ON(ret);
 
-        btrfs_record_root_in_trans(root);
         h->transid = root->fs_info->running_transaction->transid;
         h->transaction = root->fs_info->running_transaction;
         h->blocks_reserved = num_blocks;
@@ -192,6 +182,7 @@ static struct btrfs_trans_handle *start_transaction(struct btrfs_root *root,
         h->delayed_ref_updates = 0;
 
         root->fs_info->running_transaction->use_count++;
+        record_root_in_trans(h, root);
         mutex_unlock(&root->fs_info->trans_mutex);
         return h;
 }
@@ -233,6 +224,7 @@ static noinline int wait_for_commit(struct btrfs_root *root,
         return 0;
 }
 
+#if 0
 /*
  * rate limit against the drop_snapshot code.  This helps to slow down new
  * operations if the drop_snapshot code isn't able to keep up.
@@ -273,6 +265,7 @@ harder:
                         goto harder;
         }
 }
+#endif
 
 void btrfs_throttle(struct btrfs_root *root)
 {
@@ -280,7 +273,6 @@ void btrfs_throttle(struct btrfs_root *root)
         if (!root->fs_info->open_ioctl_trans)
                 wait_current_trans(root);
         mutex_unlock(&root->fs_info->trans_mutex);
-        throttle_on_drops(root);
 }
 
 static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
@@ -323,9 +315,6 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
         memset(trans, 0, sizeof(*trans));
         kmem_cache_free(btrfs_trans_handle_cachep, trans);
 
-        if (throttle)
-                throttle_on_drops(root);
-
         return 0;
 }
 
@@ -462,12 +451,8 @@ static int update_cowonly_root(struct btrfs_trans_handle *trans,
                 old_root_bytenr = btrfs_root_bytenr(&root->root_item);
                 if (old_root_bytenr == root->node->start)
                         break;
-                btrfs_set_root_bytenr(&root->root_item,
-                                       root->node->start);
-                btrfs_set_root_level(&root->root_item,
-                                     btrfs_header_level(root->node));
-                btrfs_set_root_generation(&root->root_item, trans->transid);
 
+                btrfs_set_root_node(&root->root_item, root->node);
                 ret = btrfs_update_root(trans, tree_root,
                                         &root->root_key,
                                         &root->root_item);
@@ -477,14 +462,16 @@ static int update_cowonly_root(struct btrfs_trans_handle *trans,
                 ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
                 BUG_ON(ret);
         }
+        free_extent_buffer(root->commit_root);
+        root->commit_root = btrfs_root_node(root);
         return 0;
 }
 
 /*
  * update all the cowonly tree roots on disk
  */
-int btrfs_commit_tree_roots(struct btrfs_trans_handle *trans,
-                            struct btrfs_root *root)
+static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans,
+                                         struct btrfs_root *root)
 {
         struct btrfs_fs_info *fs_info = root->fs_info;
         struct list_head *next;
@@ -520,118 +507,54 @@ int btrfs_commit_tree_roots(struct btrfs_trans_handle *trans,
  * a dirty root struct and adds it into the list of dead roots that need to
  * be deleted
  */
-int btrfs_add_dead_root(struct btrfs_root *root, struct btrfs_root *latest)
+int btrfs_add_dead_root(struct btrfs_root *root)
 {
-        struct btrfs_dirty_root *dirty;
-
-        dirty = kmalloc(sizeof(*dirty), GFP_NOFS);
-        if (!dirty)
-                return -ENOMEM;
-        dirty->root = root;
-        dirty->latest_root = latest;
-
         mutex_lock(&root->fs_info->trans_mutex);
-        list_add(&dirty->list, &latest->fs_info->dead_roots);
+        list_add(&root->root_list, &root->fs_info->dead_roots);
         mutex_unlock(&root->fs_info->trans_mutex);
         return 0;
 }
 
 /*
- * at transaction commit time we need to schedule the old roots for
- * deletion via btrfs_drop_snapshot.  This runs through all the
- * reference counted roots that were modified in the current
- * transaction and puts them into the drop list
+ * update all the cowonly tree roots on disk
  */
-static noinline int add_dirty_roots(struct btrfs_trans_handle *trans,
-                                    struct radix_tree_root *radix,
-                                    struct list_head *list)
+static noinline int commit_fs_roots(struct btrfs_trans_handle *trans,
+                                    struct btrfs_root *root)
 {
-        struct btrfs_dirty_root *dirty;
         struct btrfs_root *gang[8];
-        struct btrfs_root *root;
+        struct btrfs_fs_info *fs_info = root->fs_info;
         int i;
         int ret;
         int err = 0;
-        u32 refs;
 
         while (1) {
-                ret = radix_tree_gang_lookup_tag(radix, (void **)gang, 0,
+                ret = radix_tree_gang_lookup_tag(&fs_info->fs_roots_radix,
+                                                 (void **)gang, 0,
                                                  ARRAY_SIZE(gang),
                                                  BTRFS_ROOT_TRANS_TAG);
                 if (ret == 0)
                         break;
                 for (i = 0; i < ret; i++) {
                         root = gang[i];
-                        radix_tree_tag_clear(radix,
-                                     (unsigned long)root->root_key.objectid,
-                                     BTRFS_ROOT_TRANS_TAG);
-
-                        BUG_ON(!root->ref_tree);
-                        dirty = root->dirty_root;
+                        radix_tree_tag_clear(&fs_info->fs_roots_radix,
+                                        (unsigned long)root->root_key.objectid,
+                                        BTRFS_ROOT_TRANS_TAG);
 
                         btrfs_free_log(trans, root);
-                        btrfs_free_reloc_root(trans, root);
-
-                        if (root->commit_root == root->node) {
-                                WARN_ON(root->node->start !=
-                                        btrfs_root_bytenr(&root->root_item));
-
-                                free_extent_buffer(root->commit_root);
-                                root->commit_root = NULL;
-                                root->dirty_root = NULL;
-
-                                spin_lock(&root->list_lock);
-                                list_del_init(&dirty->root->dead_list);
-                                spin_unlock(&root->list_lock);
+                        btrfs_update_reloc_root(trans, root);
 
-                                kfree(dirty->root);
-                                kfree(dirty);
-
-                                /* make sure to update the root on disk
-                                 * so we get any updates to the block used
-                                 * counts
-                                 */
-                                err = btrfs_update_root(trans,
-                                                root->fs_info->tree_root,
-                                                &root->root_key,
-                                                &root->root_item);
+                        if (root->commit_root == root->node)
                                 continue;
-                        }
 
-                        memset(&root->root_item.drop_progress, 0,
-                               sizeof(struct btrfs_disk_key));
-                        root->root_item.drop_level = 0;
-                        root->commit_root = NULL;
-                        root->dirty_root = NULL;
-                        root->root_key.offset = root->fs_info->generation;
-                        btrfs_set_root_bytenr(&root->root_item,
-                                              root->node->start);
-                        btrfs_set_root_level(&root->root_item,
-                                             btrfs_header_level(root->node));
-                        btrfs_set_root_generation(&root->root_item,
-                                                  root->root_key.offset);
-
-                        err = btrfs_insert_root(trans, root->fs_info->tree_root,
+                        free_extent_buffer(root->commit_root);
+                        root->commit_root = btrfs_root_node(root);
+
+                        btrfs_set_root_node(&root->root_item, root->node);
+                        err = btrfs_update_root(trans, fs_info->tree_root,
                                                 &root->root_key,
                                                 &root->root_item);
                         if (err)
                                 break;
-
-                        refs = btrfs_root_refs(&dirty->root->root_item);
-                        btrfs_set_root_refs(&dirty->root->root_item, refs - 1);
-                        err = btrfs_update_root(trans, root->fs_info->tree_root,
-                                                &dirty->root->root_key,
-                                                &dirty->root->root_item);
-
-                        BUG_ON(err);
-                        if (refs == 1) {
-                                list_add(&dirty->list, list);
-                        } else {
-                                WARN_ON(1);
-                                free_extent_buffer(dirty->root->node);
-                                kfree(dirty->root);
-                                kfree(dirty);
-                        }
                 }
         }
         return err;
@@ -688,12 +611,8 @@ static noinline int wait_transaction_pre_flush(struct btrfs_fs_info *info)
                                 TASK_UNINTERRUPTIBLE);
                 mutex_unlock(&info->trans_mutex);
 
-                atomic_dec(&info->throttles);
-                wake_up(&info->transaction_throttle);
-
                 schedule();
 
-                atomic_inc(&info->throttles);
                 mutex_lock(&info->trans_mutex);
                 finish_wait(&info->transaction_wait, &wait);
         }
@@ -705,111 +624,61 @@ static noinline int wait_transaction_pre_flush(struct btrfs_fs_info *info)
  * Given a list of roots that need to be deleted, call btrfs_drop_snapshot on
  * all of them
  */
-static noinline int drop_dirty_roots(struct btrfs_root *tree_root,
-                                     struct list_head *list)
+int btrfs_drop_dead_root(struct btrfs_root *root)
 {
-        struct btrfs_dirty_root *dirty;
         struct btrfs_trans_handle *trans;
+        struct btrfs_root *tree_root = root->fs_info->tree_root;
         unsigned long nr;
-        u64 num_bytes;
-        u64 bytes_used;
-        u64 max_useless;
-        int ret = 0;
-        int err;
-
-        while (!list_empty(list)) {
-                struct btrfs_root *root;
-
-                dirty = list_entry(list->prev, struct btrfs_dirty_root, list);
-                list_del_init(&dirty->list);
-
-                num_bytes = btrfs_root_used(&dirty->root->root_item);
-                root = dirty->latest_root;
-                atomic_inc(&root->fs_info->throttles);
-
-                while (1) {
-                        /*
-                         * we don't want to jump in and create a bunch of
-                         * delayed refs if the transaction is starting to close
-                         */
-                        wait_transaction_pre_flush(tree_root->fs_info);
-                        trans = btrfs_start_transaction(tree_root, 1);
-
-                        /*
-                         * we've joined a transaction, make sure it isn't
-                         * closing right now
-                         */
-                        if (trans->transaction->delayed_refs.flushing) {
-                                btrfs_end_transaction(trans, tree_root);
-                                continue;
-                        }
-
-                        mutex_lock(&root->fs_info->drop_mutex);
-                        ret = btrfs_drop_snapshot(trans, dirty->root);
-                        if (ret != -EAGAIN)
-                                break;
-                        mutex_unlock(&root->fs_info->drop_mutex);
+        int ret;
 
-                        err = btrfs_update_root(trans,
-                                        tree_root,
-                                        &dirty->root->root_key,
-                                        &dirty->root->root_item);
-                        if (err)
-                                ret = err;
-                        nr = trans->blocks_used;
-                        ret = btrfs_end_transaction(trans, tree_root);
-                        BUG_ON(ret);
+        while (1) {
+                /*
+                 * we don't want to jump in and create a bunch of
+                 * delayed refs if the transaction is starting to close
+                 */
+                wait_transaction_pre_flush(tree_root->fs_info);
+                trans = btrfs_start_transaction(tree_root, 1);
 
-                        btrfs_btree_balance_dirty(tree_root, nr);
-                        cond_resched();
+                /*
+                 * we've joined a transaction, make sure it isn't
+                 * closing right now
+                 */
+                if (trans->transaction->delayed_refs.flushing) {
+                        btrfs_end_transaction(trans, tree_root);
+                        continue;
                 }
-                BUG_ON(ret);
-                atomic_dec(&root->fs_info->throttles);
-                wake_up(&root->fs_info->transaction_throttle);
 
-                num_bytes -= btrfs_root_used(&dirty->root->root_item);
-                bytes_used = btrfs_root_used(&root->root_item);
-                if (num_bytes) {
-                        mutex_lock(&root->fs_info->trans_mutex);
-                        btrfs_record_root_in_trans(root);
-                        mutex_unlock(&root->fs_info->trans_mutex);
-                        btrfs_set_root_used(&root->root_item,
-                                            bytes_used - num_bytes);
-                }
+                ret = btrfs_drop_snapshot(trans, root);
+                if (ret != -EAGAIN)
+                        break;
 
-                ret = btrfs_del_root(trans, tree_root, &dirty->root->root_key);
-                if (ret) {
-                        BUG();
+                ret = btrfs_update_root(trans, tree_root,
+                                        &root->root_key,
+                                        &root->root_item);
+                if (ret)
                         break;
-                }
-                mutex_unlock(&root->fs_info->drop_mutex);
-
-                spin_lock(&root->list_lock);
-                list_del_init(&dirty->root->dead_list);
-                if (!list_empty(&root->dead_list)) {
-                        struct btrfs_root *oldest;
-                        oldest = list_entry(root->dead_list.prev,
-                                            struct btrfs_root, dead_list);
-                        max_useless = oldest->root_key.offset - 1;
-                } else {
-                        max_useless = root->root_key.offset - 1;
-                }
-                spin_unlock(&root->list_lock);
 
                 nr = trans->blocks_used;
                 ret = btrfs_end_transaction(trans, tree_root);
                 BUG_ON(ret);
 
-                ret = btrfs_remove_leaf_refs(root, max_useless, 0);
-                BUG_ON(ret);
-
-                free_extent_buffer(dirty->root->node);
-                kfree(dirty->root);
-                kfree(dirty);
-
                 btrfs_btree_balance_dirty(tree_root, nr);
                 cond_resched();
         }
+        BUG_ON(ret);
+
+        ret = btrfs_del_root(trans, tree_root, &root->root_key);
+        BUG_ON(ret);
+
+        nr = trans->blocks_used;
+        ret = btrfs_end_transaction(trans, tree_root);
+        BUG_ON(ret);
+
+        free_extent_buffer(root->node);
+        free_extent_buffer(root->commit_root);
+        kfree(root);
+
+        btrfs_btree_balance_dirty(tree_root, nr);
         return ret;
 }
 
@@ -839,24 +708,23 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
         if (ret)
                 goto fail;
 
-        btrfs_record_root_in_trans(root);
+        record_root_in_trans(trans, root);
         btrfs_set_root_last_snapshot(&root->root_item, trans->transid);
         memcpy(new_root_item, &root->root_item, sizeof(*new_root_item));
 
         key.objectid = objectid;
-        key.offset = trans->transid;
+        key.offset = 0;
         btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);
 
         old = btrfs_lock_root_node(root);
         btrfs_cow_block(trans, root, old, NULL, 0, &old);
+        btrfs_set_lock_blocking(old);
 
         btrfs_copy_root(trans, root, old, &tmp, objectid);
         btrfs_tree_unlock(old);
         free_extent_buffer(old);
 
-        btrfs_set_root_bytenr(new_root_item, tmp->start);
-        btrfs_set_root_level(new_root_item, btrfs_header_level(tmp));
-        btrfs_set_root_generation(new_root_item, trans->transid);
+        btrfs_set_root_node(new_root_item, tmp);
         ret = btrfs_insert_root(trans, root->fs_info->tree_root, &key,
                                 new_root_item);
         btrfs_tree_unlock(tmp);
@@ -964,6 +832,24 @@ static noinline int finish_pending_snapshots(struct btrfs_trans_handle *trans,
         return 0;
 }
 
+static void update_super_roots(struct btrfs_root *root)
+{
+        struct btrfs_root_item *root_item;
+        struct btrfs_super_block *super;
+
+        super = &root->fs_info->super_copy;
+
+        root_item = &root->fs_info->chunk_root->root_item;
+        super->chunk_root = root_item->bytenr;
+        super->chunk_root_generation = root_item->generation;
+        super->chunk_root_level = root_item->level;
+
+        root_item = &root->fs_info->tree_root->root_item;
+        super->root = root_item->bytenr;
+        super->generation = root_item->generation;
+        super->root_level = root_item->level;
+}
+
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root)
 {
@@ -971,8 +857,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
         unsigned long timeout = 1;
         struct btrfs_transaction *cur_trans;
         struct btrfs_transaction *prev_trans = NULL;
-        struct btrfs_root *chunk_root = root->fs_info->chunk_root;
-        struct list_head dirty_fs_roots;
         struct extent_io_tree *pinned_copy;
         DEFINE_WAIT(wait);
         int ret;
@@ -999,7 +883,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
         BUG_ON(ret);
 
         mutex_lock(&root->fs_info->trans_mutex);
-        INIT_LIST_HEAD(&dirty_fs_roots);
         if (cur_trans->in_commit) {
                 cur_trans->use_count++;
                 mutex_unlock(&root->fs_info->trans_mutex);
@@ -1105,41 +988,36 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
          * with the tree-log code.
          */
         mutex_lock(&root->fs_info->tree_log_mutex);
-        /*
-         * keep tree reloc code from adding new reloc trees
-         */
-        mutex_lock(&root->fs_info->tree_reloc_mutex);
-
 
-        ret = add_dirty_roots(trans, &root->fs_info->fs_roots_radix,
-                              &dirty_fs_roots);
+        ret = commit_fs_roots(trans, root);
         BUG_ON(ret);
 
-        /* add_dirty_roots gets rid of all the tree log roots, it is now
+        /* commit_fs_roots gets rid of all the tree log roots, it is now
          * safe to free the root of tree log roots
          */
         btrfs_free_log_root_tree(trans, root->fs_info);
 
-        ret = btrfs_commit_tree_roots(trans, root);
+        ret = commit_cowonly_roots(trans, root);
         BUG_ON(ret);
 
         cur_trans = root->fs_info->running_transaction;
         spin_lock(&root->fs_info->new_trans_lock);
         root->fs_info->running_transaction = NULL;
         spin_unlock(&root->fs_info->new_trans_lock);
-        btrfs_set_super_generation(&root->fs_info->super_copy,
-                                   cur_trans->transid);
-        btrfs_set_super_root(&root->fs_info->super_copy,
-                             root->fs_info->tree_root->node->start);
-        btrfs_set_super_root_level(&root->fs_info->super_copy,
-                           btrfs_header_level(root->fs_info->tree_root->node));
-
-        btrfs_set_super_chunk_root(&root->fs_info->super_copy,
-                                   chunk_root->node->start);
-        btrfs_set_super_chunk_root_level(&root->fs_info->super_copy,
-                                         btrfs_header_level(chunk_root->node));
-        btrfs_set_super_chunk_root_generation(&root->fs_info->super_copy,
-                                btrfs_header_generation(chunk_root->node));
+
+        btrfs_set_root_node(&root->fs_info->tree_root->root_item,
+                            root->fs_info->tree_root->node);
+        free_extent_buffer(root->fs_info->tree_root->commit_root);
+        root->fs_info->tree_root->commit_root =
+                                btrfs_root_node(root->fs_info->tree_root);
+
+        btrfs_set_root_node(&root->fs_info->chunk_root->root_item,
+                            root->fs_info->chunk_root->node);
+        free_extent_buffer(root->fs_info->chunk_root->commit_root);
+        root->fs_info->chunk_root->commit_root =
+                                btrfs_root_node(root->fs_info->chunk_root);
+
+        update_super_roots(root);
 
         if (!root->fs_info->log_root_recovering) {
                 btrfs_set_super_log_root(&root->fs_info->super_copy, 0);
@@ -1153,7 +1031,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
         trans->transaction->blocked = 0;
 
-        wake_up(&root->fs_info->transaction_throttle);
         wake_up(&root->fs_info->transaction_wait);
 
         mutex_unlock(&root->fs_info->trans_mutex);
@@ -1170,9 +1047,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
         btrfs_finish_extent_commit(trans, root, pinned_copy);
         kfree(pinned_copy);
 
-        btrfs_drop_dead_reloc_roots(root);
-        mutex_unlock(&root->fs_info->tree_reloc_mutex);
-
         /* do the directory inserts of any pending snapshot creations */
         finish_pending_snapshots(trans, root->fs_info);
 
@@ -1186,16 +1060,9 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
         put_transaction(cur_trans);
         put_transaction(cur_trans);
 
-        list_splice_init(&dirty_fs_roots, &root->fs_info->dead_roots);
-        if (root->fs_info->closing)
-                list_splice_init(&root->fs_info->dead_roots, &dirty_fs_roots);
-
         mutex_unlock(&root->fs_info->trans_mutex);
 
         kmem_cache_free(btrfs_trans_handle_cachep, trans);
-
-        if (root->fs_info->closing)
-                drop_dirty_roots(root->fs_info->tree_root, &dirty_fs_roots);
         return ret;
 }
 
@@ -1204,16 +1071,17 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
  */
 int btrfs_clean_old_snapshots(struct btrfs_root *root)
 {
-        struct list_head dirty_roots;
-        INIT_LIST_HEAD(&dirty_roots);
-again:
-        mutex_lock(&root->fs_info->trans_mutex);
-        list_splice_init(&root->fs_info->dead_roots, &dirty_roots);
-        mutex_unlock(&root->fs_info->trans_mutex);
+        LIST_HEAD(list);
+        struct btrfs_fs_info *fs_info = root->fs_info;
+
+        mutex_lock(&fs_info->trans_mutex);
+        list_splice_init(&fs_info->dead_roots, &list);
+        mutex_unlock(&fs_info->trans_mutex);
 
-        if (!list_empty(&dirty_roots)) {
-                drop_dirty_roots(root, &dirty_roots);
-                goto again;
+        while (!list_empty(&list)) {
+                root = list_entry(list.next, struct btrfs_root, root_list);
+                list_del_init(&root->root_list);
+                btrfs_drop_dead_root(root);
         }
         return 0;
 }