1 files changed, 794 insertions, 302 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index edc7d208c5ce..72a2b9c28e9f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -21,6 +21,7 @@
 #include <linux/blkdev.h>
 #include <linux/sort.h>
 #include <linux/rcupdate.h>
+#include <linux/kthread.h>
 #include "compat.h"
 #include "hash.h"
 #include "ctree.h"
@@ -61,6 +62,13 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
                           struct btrfs_root *extent_root, u64 alloc_bytes,
                           u64 flags, int force);
 
+static noinline int
+block_group_cache_done(struct btrfs_block_group_cache *cache)
+{
+        smp_mb();
+        return cache->cached == BTRFS_CACHE_FINISHED;
+}
+
 static int block_group_bits(struct btrfs_block_group_cache *cache, u64 bits)
 {
         return (cache->flags & bits) == bits;
@@ -146,20 +154,70 @@ block_group_cache_tree_search(struct btrfs_fs_info *info, u64 bytenr,
 }
 
 /*
+ * We always set EXTENT_LOCKED for the super mirror extents so we don't
+ * overwrite them, so those bits need to be unset.  Also, if we are unmounting
+ * with pinned extents still sitting there because we had a block group caching,
+ * we need to clear those now, since we are done.
+ */
+void btrfs_free_pinned_extents(struct btrfs_fs_info *info)
+{
+        u64 start, end, last = 0;
+        int ret;
+
+        while (1) {
+                ret = find_first_extent_bit(&info->pinned_extents, last,
+                                            &start, &end,
+                                            EXTENT_LOCKED|EXTENT_DIRTY);
+                if (ret)
+                        break;
+
+                clear_extent_bits(&info->pinned_extents, start, end,
+                                  EXTENT_LOCKED|EXTENT_DIRTY, GFP_NOFS);
+                last = end+1;
+        }
+}
+
+static int remove_sb_from_cache(struct btrfs_root *root,
+                                struct btrfs_block_group_cache *cache)
+{
+        struct btrfs_fs_info *fs_info = root->fs_info;
+        u64 bytenr;
+        u64 *logical;
+        int stripe_len;
+        int i, nr, ret;
+
+        for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
+                bytenr = btrfs_sb_offset(i);
+                ret = btrfs_rmap_block(&root->fs_info->mapping_tree,
+                                       cache->key.objectid, bytenr,
+                                       0, &logical, &nr, &stripe_len);
+                BUG_ON(ret);
+                while (nr--) {
+                        try_lock_extent(&fs_info->pinned_extents,
+                                        logical[nr],
+                                        logical[nr] + stripe_len - 1, GFP_NOFS);
+                }
+                kfree(logical);
+        }
+
+        return 0;
+}
+
+/*
  * this is only called by cache_block_group, since we could have freed extents
  * we need to check the pinned_extents for any extents that can't be used yet
  * since their free space will be released as soon as the transaction commits.
  */
-static int add_new_free_space(struct btrfs_block_group_cache *block_group,
+static u64 add_new_free_space(struct btrfs_block_group_cache *block_group,
                               struct btrfs_fs_info *info, u64 start, u64 end)
 {
-        u64 extent_start, extent_end, size;
+        u64 extent_start, extent_end, size, total_added = 0;
         int ret;
 
         while (start < end) {
                 ret = find_first_extent_bit(&info->pinned_extents, start,
                                             &extent_start, &extent_end,
-                                            EXTENT_DIRTY);
+                                            EXTENT_DIRTY|EXTENT_LOCKED);
                 if (ret)
                         break;
 
@@ -167,6 +225,7 @@ static int add_new_free_space(struct btrfs_block_group_cache *block_group,
                         start = extent_end + 1;
                 } else if (extent_start > start && extent_start < end) {
                         size = extent_start - start;
+                        total_added += size;
                         ret = btrfs_add_free_space(block_group, start,
                                                    size);
                         BUG_ON(ret);
@@ -178,84 +237,93 @@ static int add_new_free_space(struct btrfs_block_group_cache *block_group,
 
         if (start < end) {
                 size = end - start;
+                total_added += size;
                 ret = btrfs_add_free_space(block_group, start, size);
                 BUG_ON(ret);
         }
 
-        return 0;
+        return total_added;
 }
 
-static int remove_sb_from_cache(struct btrfs_root *root,
-                                struct btrfs_block_group_cache *cache)
-{
-        u64 bytenr;
-        u64 *logical;
-        int stripe_len;
-        int i, nr, ret;
-
-        for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
-                bytenr = btrfs_sb_offset(i);
-                ret = btrfs_rmap_block(&root->fs_info->mapping_tree,
-                                       cache->key.objectid, bytenr, 0,
-                                       &logical, &nr, &stripe_len);
-                BUG_ON(ret);
-                while (nr--) {
-                        btrfs_remove_free_space(cache, logical[nr],
-                                                stripe_len);
-                }
-                kfree(logical);
-        }
-        return 0;
-}
-
-static int cache_block_group(struct btrfs_root *root,
-                             struct btrfs_block_group_cache *block_group)
+static int caching_kthread(void *data)
 {
+        struct btrfs_block_group_cache *block_group = data;
+        struct btrfs_fs_info *fs_info = block_group->fs_info;
+        u64 last = 0;
         struct btrfs_path *path;
         int ret = 0;
         struct btrfs_key key;
         struct extent_buffer *leaf;
         int slot;
-        u64 last;
+        u64 total_found = 0;
 
-        if (!block_group)
-                return 0;
-
-        root = root->fs_info->extent_root;
-
-        if (block_group->cached)
-                return 0;
+        BUG_ON(!fs_info);
 
         path = btrfs_alloc_path();
         if (!path)
                 return -ENOMEM;
 
-        path->reada = 2;
+        atomic_inc(&block_group->space_info->caching_threads);
+        last = max_t(u64, block_group->key.objectid, BTRFS_SUPER_INFO_OFFSET);
         /*
-         * we get into deadlocks with paths held by callers of this function.
-         * since the alloc_mutex is protecting things right now, just
-         * skip the locking here
+         * We don't want to deadlock with somebody trying to allocate a new
+         * extent for the extent root while also trying to search the extent
+         * root to add free space.  So we skip locking and search the commit
+         * root, since its read-only
          */
         path->skip_locking = 1;
-        last = max_t(u64, block_group->key.objectid, BTRFS_SUPER_INFO_OFFSET);
+        path->search_commit_root = 1;
+        path->reada = 2;
+
         key.objectid = last;
         key.offset = 0;
         btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
-        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+again:
+        /* need to make sure the commit_root doesn't disappear */
+        down_read(&fs_info->extent_commit_sem);
+
+        ret = btrfs_search_slot(NULL, fs_info->extent_root, &key, path, 0, 0);
         if (ret < 0)
                 goto err;
 
         while (1) {
+                smp_mb();
+                if (block_group->fs_info->closing > 1) {
+                        last = (u64)-1;
+                        break;
+                }
+
                 leaf = path->nodes[0];
                 slot = path->slots[0];
                 if (slot >= btrfs_header_nritems(leaf)) {
-                        ret = btrfs_next_leaf(root, path);
+                        ret = btrfs_next_leaf(fs_info->extent_root, path);
                         if (ret < 0)
                                 goto err;
-                        if (ret == 0)
-                                continue;
-                        else
+                        else if (ret)
                                 break;
+
+                        if (need_resched() ||
+                            btrfs_transaction_in_commit(fs_info)) {
+                                leaf = path->nodes[0];
+
+                                /* this shouldn't happen, but if the
+                                 * leaf is empty just move on.
+                                 */
+                                if (btrfs_header_nritems(leaf) == 0)
+                                        break;
+                                /*
+                                 * we need to copy the key out so that
+                                 * we are sure the next search advances
+                                 * us forward in the btree.
+                                 */
+                                btrfs_item_key_to_cpu(leaf, &key, 0);
+                                btrfs_release_path(fs_info->extent_root, path);
+                                up_read(&fs_info->extent_commit_sem);
+                                schedule_timeout(1);
+                                goto again;
+                        }
+
+                        continue;
                 }
                 btrfs_item_key_to_cpu(leaf, &key, slot);
                 if (key.objectid < block_group->key.objectid)
@@ -266,24 +334,59 @@ static int cache_block_group(struct btrfs_root *root,
                         break;
 
                 if (btrfs_key_type(&key) == BTRFS_EXTENT_ITEM_KEY) {
-                        add_new_free_space(block_group, root->fs_info, last,
-                                           key.objectid);
-
+                        total_found += add_new_free_space(block_group,
+                                                          fs_info, last,
+                                                          key.objectid);
                         last = key.objectid + key.offset;
                 }
+
+                if (total_found > (1024 * 1024 * 2)) {
+                        total_found = 0;
+                        wake_up(&block_group->caching_q);
+                }
 next:
                 path->slots[0]++;
         }
+        ret = 0;
 
-        add_new_free_space(block_group, root->fs_info, last,
-                           block_group->key.objectid +
-                           block_group->key.offset);
+        total_found += add_new_free_space(block_group, fs_info, last,
+                                          block_group->key.objectid +
+                                          block_group->key.offset);
+
+        spin_lock(&block_group->lock);
+        block_group->cached = BTRFS_CACHE_FINISHED;
+        spin_unlock(&block_group->lock);
 
-        block_group->cached = 1;
-        remove_sb_from_cache(root, block_group);
-        ret = 0;
 err:
         btrfs_free_path(path);
+        up_read(&fs_info->extent_commit_sem);
+        atomic_dec(&block_group->space_info->caching_threads);
+        wake_up(&block_group->caching_q);
+
+        return 0;
+}
+
+static int cache_block_group(struct btrfs_block_group_cache *cache)
+{
+        struct task_struct *tsk;
+        int ret = 0;
+
+        spin_lock(&cache->lock);
+        if (cache->cached != BTRFS_CACHE_NO) {
+                spin_unlock(&cache->lock);
+                return ret;
+        }
+        cache->cached = BTRFS_CACHE_STARTED;
+        spin_unlock(&cache->lock);
+
+        tsk = kthread_run(caching_kthread, cache, "btrfs-cache-%llu\n",
+                          cache->key.objectid);
+        if (IS_ERR(tsk)) {
+                ret = PTR_ERR(tsk);
+                printk(KERN_ERR "error running thread %d\n", ret);
+                BUG();
+        }
+
         return ret;
 }
 
@@ -990,15 +1093,13 @@ static inline int extent_ref_type(u64 parent, u64 owner)
         return type;
 }
 
-static int find_next_key(struct btrfs_path *path, struct btrfs_key *key)
+static int find_next_key(struct btrfs_path *path, int level,
+                         struct btrfs_key *key)
 
 {
-        int level;
-        BUG_ON(!path->keep_locks);
-        for (level = 0; level < BTRFS_MAX_LEVEL; level++) {
+        for (; level < BTRFS_MAX_LEVEL; level++) {
                 if (!path->nodes[level])
                         break;
-                btrfs_assert_tree_locked(path->nodes[level]);
                 if (path->slots[level] + 1 >=
                     btrfs_header_nritems(path->nodes[level]))
                         continue;
@@ -1158,7 +1259,8 @@ int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
                  * For simplicity, we just do not add new inline back
                  * ref if there is any kind of item for this block
                  */
-                if (find_next_key(path, &key) == 0 && key.objectid == bytenr &&
+                if (find_next_key(path, 0, &key) == 0 &&
+                    key.objectid == bytenr &&
                     key.type < BTRFS_BLOCK_GROUP_ITEM_KEY) {
                         err = -EAGAIN;
                         goto out;
@@ -2388,13 +2490,29 @@ fail:
 
 }
 
+static struct btrfs_block_group_cache *
+next_block_group(struct btrfs_root *root,
+                 struct btrfs_block_group_cache *cache)
+{
+        struct rb_node *node;
+        spin_lock(&root->fs_info->block_group_cache_lock);
+        node = rb_next(&cache->cache_node);
+        btrfs_put_block_group(cache);
+        if (node) {
+                cache = rb_entry(node, struct btrfs_block_group_cache,
+                                 cache_node);
+                atomic_inc(&cache->count);
+        } else
+                cache = NULL;
+        spin_unlock(&root->fs_info->block_group_cache_lock);
+        return cache;
+}
+
 int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
                                    struct btrfs_root *root)
 {
-        struct btrfs_block_group_cache *cache, *entry;
-        struct rb_node *n;
+        struct btrfs_block_group_cache *cache;
         int err = 0;
-        int werr = 0;
         struct btrfs_path *path;
         u64 last = 0;
 
@@ -2403,39 +2521,35 @@ int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
                 return -ENOMEM;
 
         while (1) {
-                cache = NULL;
-                spin_lock(&root->fs_info->block_group_cache_lock);
-                for (n = rb_first(&root->fs_info->block_group_cache_tree);
-                     n; n = rb_next(n)) {
-                        entry = rb_entry(n, struct btrfs_block_group_cache,
-                                         cache_node);
-                        if (entry->dirty) {
-                                cache = entry;
-                                break;
-                        }
+                if (last == 0) {
+                        err = btrfs_run_delayed_refs(trans, root,
+                                                     (unsigned long)-1);
+                        BUG_ON(err);
                 }
-                spin_unlock(&root->fs_info->block_group_cache_lock);
 
-                if (!cache)
-                        break;
+                cache = btrfs_lookup_first_block_group(root->fs_info, last);
+                while (cache) {
+                        if (cache->dirty)
+                                break;
+                        cache = next_block_group(root, cache);
+                }
+                if (!cache) {
+                        if (last == 0)
+                                break;
+                        last = 0;
+                        continue;
+                }
 
                 cache->dirty = 0;
-                last += cache->key.offset;
+                last = cache->key.objectid + cache->key.offset;
 
-                err = write_one_cache_group(trans, root,
-                                            path, cache);
-                /*
-                 * if we fail to write the cache group, we want
-                 * to keep it marked dirty in hopes that a later
-                 * write will work
-                 */
-                if (err) {
-                        werr = err;
-                        continue;
-                }
+                err = write_one_cache_group(trans, root, path, cache);
+                BUG_ON(err);
+                btrfs_put_block_group(cache);
         }
+
         btrfs_free_path(path);
-        return werr;
+        return 0;
 }
 
 int btrfs_extent_readonly(struct btrfs_root *root, u64 bytenr)
@@ -2485,6 +2599,7 @@ static int update_space_info(struct btrfs_fs_info *info, u64 flags,
         found->force_alloc = 0;
         *space_info = found;
         list_add_rcu(&found->list, &info->space_info);
+        atomic_set(&found->caching_threads, 0);
         return 0;
 }
 
@@ -2697,7 +2812,7 @@ again:
 
                 printk(KERN_ERR "no space left, need %llu, %llu delalloc bytes"
                        ", %llu bytes_used, %llu bytes_reserved, "
-                       "%llu bytes_pinned, %llu bytes_readonly, %llu may use"
+                       "%llu bytes_pinned, %llu bytes_readonly, %llu may use "
                        "%llu total\n", (unsigned long long)bytes,
                        (unsigned long long)data_sinfo->bytes_delalloc,
                        (unsigned long long)data_sinfo->bytes_used,
@@ -2948,13 +3063,9 @@ int btrfs_update_pinned_extents(struct btrfs_root *root,
         struct btrfs_block_group_cache *cache;
         struct btrfs_fs_info *fs_info = root->fs_info;
 
-        if (pin) {
+        if (pin)
                 set_extent_dirty(&fs_info->pinned_extents,
                                 bytenr, bytenr + num - 1, GFP_NOFS);
-        } else {
-                clear_extent_dirty(&fs_info->pinned_extents,
-                                bytenr, bytenr + num - 1, GFP_NOFS);
-        }
 
         while (num > 0) {
                 cache = btrfs_lookup_block_group(fs_info, bytenr);
@@ -2970,14 +3081,34 @@ int btrfs_update_pinned_extents(struct btrfs_root *root,
                         spin_unlock(&cache->space_info->lock);
                         fs_info->total_pinned += len;
                 } else {
+                        int unpin = 0;
+
+                        /*
+                         * in order to not race with the block group caching, we
+                         * only want to unpin the extent if we are cached.  If
+                         * we aren't cached, we want to start async caching this
+                         * block group so we can free the extent the next time
+                         * around.
+                         */
                         spin_lock(&cache->space_info->lock);
                         spin_lock(&cache->lock);
-                        cache->pinned -= len;
-                        cache->space_info->bytes_pinned -= len;
+                        unpin = (cache->cached == BTRFS_CACHE_FINISHED);
+                        if (likely(unpin)) {
+                                cache->pinned -= len;
+                                cache->space_info->bytes_pinned -= len;
+                                fs_info->total_pinned -= len;
+                        }
                         spin_unlock(&cache->lock);
                         spin_unlock(&cache->space_info->lock);
-                        fs_info->total_pinned -= len;
-                        if (cache->cached)
+
+                        if (likely(unpin))
+                                clear_extent_dirty(&fs_info->pinned_extents,
+                                                   bytenr, bytenr + len -1,
+                                                   GFP_NOFS);
+                        else
+                                cache_block_group(cache);
+
+                        if (unpin)
                                 btrfs_add_free_space(cache, bytenr, len);
                 }
                 btrfs_put_block_group(cache);
@@ -3031,6 +3162,7 @@ int btrfs_copy_pinned(struct btrfs_root *root, struct extent_io_tree *copy)
                                             &start, &end, EXTENT_DIRTY);
                 if (ret)
                         break;
+
                 set_extent_dirty(copy, start, end, GFP_NOFS);
                 last = end + 1;
         }
@@ -3059,6 +3191,7 @@ int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans,
 
                 cond_resched();
         }
+
         return ret;
 }
 
@@ -3437,6 +3570,45 @@ static u64 stripe_align(struct btrfs_root *root, u64 val)
 }
 
 /*
+ * when we wait for progress in the block group caching, its because
+ * our allocation attempt failed at least once.  So, we must sleep
+ * and let some progress happen before we try again.
+ *
+ * This function will sleep at least once waiting for new free space to
+ * show up, and then it will check the block group free space numbers
+ * for our min num_bytes.  Another option is to have it go ahead
+ * and look in the rbtree for a free extent of a given size, but this
+ * is a good start.
+ */
+static noinline int
+wait_block_group_cache_progress(struct btrfs_block_group_cache *cache,
+                                u64 num_bytes)
+{
+        DEFINE_WAIT(wait);
+
+        prepare_to_wait(&cache->caching_q, &wait, TASK_UNINTERRUPTIBLE);
+
+        if (block_group_cache_done(cache)) {
+                finish_wait(&cache->caching_q, &wait);
+                return 0;
+        }
+        schedule();
+        finish_wait(&cache->caching_q, &wait);
+
+        wait_event(cache->caching_q, block_group_cache_done(cache) ||
+                   (cache->free_space >= num_bytes));
+        return 0;
+}
+
+enum btrfs_loop_type {
+        LOOP_CACHED_ONLY = 0,
+        LOOP_CACHING_NOWAIT = 1,
+        LOOP_CACHING_WAIT = 2,
+        LOOP_ALLOC_CHUNK = 3,
+        LOOP_NO_EMPTY_SIZE = 4,
+};
+
+/*
  * walks the btree of allocated extents and find a hole of a given size.
  * The key ins is changed to record the hole:
  * ins->objectid == block start
@@ -3461,6 +3633,7 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
         struct btrfs_space_info *space_info;
         int last_ptr_loop = 0;
         int loop = 0;
+        bool found_uncached_bg = false;
 
         WARN_ON(num_bytes < root->sectorsize);
         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
@@ -3492,15 +3665,18 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
         search_start = max(search_start, first_logical_byte(root, 0));
         search_start = max(search_start, hint_byte);
 
-        if (!last_ptr) {
+        if (!last_ptr)
                 empty_cluster = 0;
-                loop = 1;
-        }
 
         if (search_start == hint_byte) {
                 block_group = btrfs_lookup_block_group(root->fs_info,
                                                        search_start);
-                if (block_group && block_group_bits(block_group, data)) {
+                /*
+                 * we don't want to use the block group if it doesn't match our
+                 * allocation bits, or if its not cached.
+                 */
+                if (block_group && block_group_bits(block_group, data) &&
+                    block_group_cache_done(block_group)) {
                         down_read(&space_info->groups_sem);
                         if (list_empty(&block_group->list) ||
                             block_group->ro) {
@@ -3523,21 +3699,35 @@ search:
         down_read(&space_info->groups_sem);
         list_for_each_entry(block_group, &space_info->block_groups, list) {
                 u64 offset;
+                int cached;
 
                 atomic_inc(&block_group->count);
                 search_start = block_group->key.objectid;
 
 have_block_group:
-                if (unlikely(!block_group->cached)) {
-                        mutex_lock(&block_group->cache_mutex);
-                        ret = cache_block_group(root, block_group);
-                        mutex_unlock(&block_group->cache_mutex);
-                        if (ret) {
-                                btrfs_put_block_group(block_group);
-                                break;
+                if (unlikely(block_group->cached == BTRFS_CACHE_NO)) {
+                        /*
+                         * we want to start caching kthreads, but not too many
+                         * right off the bat so we don't overwhelm the system,
+                         * so only start them if there are less than 2 and we're
+                         * in the initial allocation phase.
+                         */
+                        if (loop > LOOP_CACHING_NOWAIT ||
+                            atomic_read(&space_info->caching_threads) < 2) {
+                                ret = cache_block_group(block_group);
+                                BUG_ON(ret);
                         }
                 }
 
+                cached = block_group_cache_done(block_group);
+                if (unlikely(!cached)) {
+                        found_uncached_bg = true;
+
+                        /* if we only want cached bgs, loop */
+                        if (loop == LOOP_CACHED_ONLY)
+                                goto loop;
+                }
+
                 if (unlikely(block_group->ro))
                         goto loop;
 
@@ -3616,14 +3806,21 @@ refill_cluster:
                                         spin_unlock(&last_ptr->refill_lock);
                                         goto checks;
                                 }
+                        } else if (!cached && loop > LOOP_CACHING_NOWAIT) {
+                                spin_unlock(&last_ptr->refill_lock);
+
+                                wait_block_group_cache_progress(block_group,
+                                       num_bytes + empty_cluster + empty_size);
+                                goto have_block_group;
                         }
+
                         /*
                          * at this point we either didn't find a cluster
                          * or we weren't able to allocate a block from our
                          * cluster.  Free the cluster we've been trying
                          * to use, and go to the next block group
                          */
-                        if (loop < 2) {
+                        if (loop < LOOP_NO_EMPTY_SIZE) {
                                 btrfs_return_cluster_to_free_space(NULL,
                                                                    last_ptr);
                                 spin_unlock(&last_ptr->refill_lock);
@@ -3634,11 +3831,17 @@ refill_cluster:
 
                 offset = btrfs_find_space_for_alloc(block_group, search_start,
                                                     num_bytes, empty_size);
-                if (!offset)
+                if (!offset && (cached || (!cached &&
+                                           loop == LOOP_CACHING_NOWAIT))) {
                         goto loop;
+                } else if (!offset && (!cached &&
+                                       loop > LOOP_CACHING_NOWAIT)) {
+                        wait_block_group_cache_progress(block_group,
+                                        num_bytes + empty_size);
+                        goto have_block_group;
+                }
 checks:
                 search_start = stripe_align(root, offset);
-
                 /* move on to the next group */
                 if (search_start + num_bytes >= search_end) {
                         btrfs_add_free_space(block_group, offset, num_bytes);
@@ -3684,13 +3887,26 @@ loop:
         }
         up_read(&space_info->groups_sem);
 
-        /* loop == 0, try to find a clustered alloc in every block group
-         * loop == 1, try again after forcing a chunk allocation
-         * loop == 2, set empty_size and empty_cluster to 0 and try again
+        /* LOOP_CACHED_ONLY, only search fully cached block groups
+         * LOOP_CACHING_NOWAIT, search partially cached block groups, but
+         *                      dont wait foR them to finish caching
+         * LOOP_CACHING_WAIT, search everything, and wait if our bg is caching
+         * LOOP_ALLOC_CHUNK, force a chunk allocation and try again
+         * LOOP_NO_EMPTY_SIZE, set empty_size and empty_cluster to 0 and try
+         *                      again
          */
-        if (!ins->objectid && loop < 3 &&
-            (empty_size || empty_cluster || allowed_chunk_alloc)) {
-                if (loop >= 2) {
+        if (!ins->objectid && loop < LOOP_NO_EMPTY_SIZE &&
+            (found_uncached_bg || empty_size || empty_cluster ||
+             allowed_chunk_alloc)) {
+                if (found_uncached_bg) {
+                        found_uncached_bg = false;
+                        if (loop < LOOP_CACHING_WAIT) {
+                                loop++;
+                                goto search;
+                        }
+                }
+
+                if (loop == LOOP_ALLOC_CHUNK) {
                         empty_size = 0;
                         empty_cluster = 0;
                 }
@@ -3703,7 +3919,7 @@ loop:
                         space_info->force_alloc = 1;
                 }
 
-                if (loop < 3) {
+                if (loop < LOOP_NO_EMPTY_SIZE) {
                         loop++;
                         goto search;
                 }
@@ -3799,7 +4015,7 @@ again:
                                num_bytes, data, 1);
                 goto again;
         }
-        if (ret) {
+        if (ret == -ENOSPC) {
                 struct btrfs_space_info *sinfo;
 
                 sinfo = __find_space_info(root->fs_info, data);
@@ -3807,7 +4023,6 @@ again:
                        "wanted %llu\n", (unsigned long long)data,
                        (unsigned long long)num_bytes);
                 dump_space_info(sinfo, num_bytes);
-                BUG();
         }
 
         return ret;
@@ -3845,7 +4060,9 @@ int btrfs_reserve_extent(struct btrfs_trans_handle *trans,
         ret = __btrfs_reserve_extent(trans, root, num_bytes, min_alloc_size,
                                      empty_size, hint_byte, search_end, ins,
                                      data);
-        update_reserved_extents(root, ins->objectid, ins->offset, 1);
+        if (!ret)
+                update_reserved_extents(root, ins->objectid, ins->offset, 1);
+
         return ret;
 }
 
@@ -4007,9 +4224,9 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
         struct btrfs_block_group_cache *block_group;
 
         block_group = btrfs_lookup_block_group(root->fs_info, ins->objectid);
-        mutex_lock(&block_group->cache_mutex);
-        cache_block_group(root, block_group);
-        mutex_unlock(&block_group->cache_mutex);
+        cache_block_group(block_group);
+        wait_event(block_group->caching_q,
+                   block_group_cache_done(block_group));
 
         ret = btrfs_remove_free_space(block_group, ins->objectid,
                                       ins->offset);
@@ -4040,7 +4257,8 @@ static int alloc_tree_block(struct btrfs_trans_handle *trans,
         ret = __btrfs_reserve_extent(trans, root, num_bytes, num_bytes,
                                      empty_size, hint_byte, search_end,
                                      ins, 0);
-        BUG_ON(ret);
+        if (ret)
+                return ret;
 
         if (root_objectid == BTRFS_TREE_RELOC_OBJECTID) {
                 if (parent == 0)
@@ -4128,6 +4346,7 @@ struct extent_buffer *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
         return buf;
 }
 
+#if 0
 int btrfs_drop_leaf_ref(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root, struct extent_buffer *leaf)
 {
@@ -4171,8 +4390,6 @@ int btrfs_drop_leaf_ref(struct btrfs_trans_handle *trans,
         return 0;
 }
 
-#if 0
-
 static noinline int cache_drop_leaf_ref(struct btrfs_trans_handle *trans,
                                         struct btrfs_root *root,
                                         struct btrfs_leaf_ref *ref)
@@ -4553,262 +4770,471 @@ out:
 }
 #endif
 
+struct walk_control {
+        u64 refs[BTRFS_MAX_LEVEL];
+        u64 flags[BTRFS_MAX_LEVEL];
+        struct btrfs_key update_progress;
+        int stage;
+        int level;
+        int shared_level;
+        int update_ref;
+        int keep_locks;
+};
+
+#define DROP_REFERENCE  1
+#define UPDATE_BACKREF  2
+
 /*
- * helper function for drop_subtree, this function is similar to
- * walk_down_tree. The main difference is that it checks reference
- * counts while tree blocks are locked.
+ * hepler to process tree block while walking down the tree.
+ *
+ * when wc->stage == DROP_REFERENCE, this function checks
+ * reference count of the block. if the block is shared and
+ * we need update back refs for the subtree rooted at the
+ * block, this function changes wc->stage to UPDATE_BACKREF
+ *
+ * when wc->stage == UPDATE_BACKREF, this function updates
+ * back refs for pointers in the block.
+ *
+ * NOTE: return value 1 means we should stop walking down.
  */
-static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
+static noinline int walk_down_proc(struct btrfs_trans_handle *trans,
                                    struct btrfs_root *root,
-                                   struct btrfs_path *path, int *level)
+                                   struct btrfs_path *path,
+                                   struct walk_control *wc)
 {
-        struct extent_buffer *next;
-        struct extent_buffer *cur;
-        struct extent_buffer *parent;
-        u64 bytenr;
-        u64 ptr_gen;
-        u64 refs;
-        u64 flags;
-        u32 blocksize;
+        int level = wc->level;
+        struct extent_buffer *eb = path->nodes[level];
+        struct btrfs_key key;
+        u64 flag = BTRFS_BLOCK_FLAG_FULL_BACKREF;
         int ret;
 
-        cur = path->nodes[*level];
-        ret = btrfs_lookup_extent_info(trans, root, cur->start, cur->len,
-                                       &refs, &flags);
-        BUG_ON(ret);
-        if (refs > 1)
-                goto out;
+        if (wc->stage == UPDATE_BACKREF &&
+            btrfs_header_owner(eb) != root->root_key.objectid)
+                return 1;
 
-        BUG_ON(!(flags & BTRFS_BLOCK_FLAG_FULL_BACKREF));
+        /*
+         * when reference count of tree block is 1, it won't increase
+         * again. once full backref flag is set, we never clear it.
+         */
+        if ((wc->stage == DROP_REFERENCE && wc->refs[level] != 1) ||
+            (wc->stage == UPDATE_BACKREF && !(wc->flags[level] & flag))) {
+                BUG_ON(!path->locks[level]);
+                ret = btrfs_lookup_extent_info(trans, root,
+                                               eb->start, eb->len,
+                                               &wc->refs[level],
+                                               &wc->flags[level]);
+                BUG_ON(ret);
+                BUG_ON(wc->refs[level] == 0);
+        }
 
-        while (*level >= 0) {
-                cur = path->nodes[*level];
-                if (*level == 0) {
-                        ret = btrfs_drop_leaf_ref(trans, root, cur);
-                        BUG_ON(ret);
-                        clean_tree_block(trans, root, cur);
-                        break;
-                }
-                if (path->slots[*level] >= btrfs_header_nritems(cur)) {
-                        clean_tree_block(trans, root, cur);
-                        break;
+        if (wc->stage == DROP_REFERENCE &&
+            wc->update_ref && wc->refs[level] > 1) {
+                BUG_ON(eb == root->node);
+                BUG_ON(path->slots[level] > 0);
+                if (level == 0)
+                        btrfs_item_key_to_cpu(eb, &key, path->slots[level]);
+                else
+                        btrfs_node_key_to_cpu(eb, &key, path->slots[level]);
+                if (btrfs_header_owner(eb) == root->root_key.objectid &&
+                    btrfs_comp_cpu_keys(&key, &wc->update_progress) >= 0) {
+                        wc->stage = UPDATE_BACKREF;
+                        wc->shared_level = level;
                 }
+        }
 
-                bytenr = btrfs_node_blockptr(cur, path->slots[*level]);
-                blocksize = btrfs_level_size(root, *level - 1);
-                ptr_gen = btrfs_node_ptr_generation(cur, path->slots[*level]);
+        if (wc->stage == DROP_REFERENCE) {
+                if (wc->refs[level] > 1)
+                        return 1;
 
-                next = read_tree_block(root, bytenr, blocksize, ptr_gen);
-                btrfs_tree_lock(next);
-                btrfs_set_lock_blocking(next);
+                if (path->locks[level] && !wc->keep_locks) {
+                        btrfs_tree_unlock(eb);
+                        path->locks[level] = 0;
+                }
+                return 0;
+        }
 
-                ret = btrfs_lookup_extent_info(trans, root, bytenr, blocksize,
-                                               &refs, &flags);
+        /* wc->stage == UPDATE_BACKREF */
+        if (!(wc->flags[level] & flag)) {
+                BUG_ON(!path->locks[level]);
+                ret = btrfs_inc_ref(trans, root, eb, 1);
                 BUG_ON(ret);
-                if (refs > 1) {
-                        parent = path->nodes[*level];
-                        ret = btrfs_free_extent(trans, root, bytenr,
-                                                blocksize, parent->start,
-                                                btrfs_header_owner(parent),
-                                                *level - 1, 0);
+                ret = btrfs_dec_ref(trans, root, eb, 0);
+                BUG_ON(ret);
+                ret = btrfs_set_disk_extent_flags(trans, root, eb->start,
+                                                  eb->len, flag, 0);
+                BUG_ON(ret);
+                wc->flags[level] |= flag;
+        }
+
+        /*
+         * the block is shared by multiple trees, so it's not good to
+         * keep the tree lock
+         */
+        if (path->locks[level] && level > 0) {
+                btrfs_tree_unlock(eb);
+                path->locks[level] = 0;
+        }
+        return 0;
+}
+
+/*
+ * hepler to process tree block while walking up the tree.
+ *
+ * when wc->stage == DROP_REFERENCE, this function drops
+ * reference count on the block.
+ *
+ * when wc->stage == UPDATE_BACKREF, this function changes
+ * wc->stage back to DROP_REFERENCE if we changed wc->stage
+ * to UPDATE_BACKREF previously while processing the block.
+ *
+ * NOTE: return value 1 means we should stop walking up.
+ */
+static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
+                                 struct btrfs_root *root,
+                                 struct btrfs_path *path,
+                                 struct walk_control *wc)
+{
+        int ret = 0;
+        int level = wc->level;
+        struct extent_buffer *eb = path->nodes[level];
+        u64 parent = 0;
+
+        if (wc->stage == UPDATE_BACKREF) {
+                BUG_ON(wc->shared_level < level);
+                if (level < wc->shared_level)
+                        goto out;
+
+                BUG_ON(wc->refs[level] <= 1);
+                ret = find_next_key(path, level + 1, &wc->update_progress);
+                if (ret > 0)
+                        wc->update_ref = 0;
+
+                wc->stage = DROP_REFERENCE;
+                wc->shared_level = -1;
+                path->slots[level] = 0;
+
+                /*
+                 * check reference count again if the block isn't locked.
+                 * we should start walking down the tree again if reference
+                 * count is one.
+                 */
+                if (!path->locks[level]) {
+                        BUG_ON(level == 0);
+                        btrfs_tree_lock(eb);
+                        btrfs_set_lock_blocking(eb);
+                        path->locks[level] = 1;
+
+                        ret = btrfs_lookup_extent_info(trans, root,
+                                                       eb->start, eb->len,
+                                                       &wc->refs[level],
+                                                       &wc->flags[level]);
                         BUG_ON(ret);
-                        path->slots[*level]++;
-                        btrfs_tree_unlock(next);
-                        free_extent_buffer(next);
-                        continue;
+                        BUG_ON(wc->refs[level] == 0);
+                        if (wc->refs[level] == 1) {
+                                btrfs_tree_unlock(eb);
+                                path->locks[level] = 0;
+                                return 1;
+                        }
+                } else {
+                        BUG_ON(level != 0);
                 }
+        }
 
-                BUG_ON(!(flags & BTRFS_BLOCK_FLAG_FULL_BACKREF));
+        /* wc->stage == DROP_REFERENCE */
+        BUG_ON(wc->refs[level] > 1 && !path->locks[level]);
 
-                *level = btrfs_header_level(next);
-                path->nodes[*level] = next;
-                path->slots[*level] = 0;
-                path->locks[*level] = 1;
-                cond_resched();
+        if (wc->refs[level] == 1) {
+                if (level == 0) {
+                        if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
+                                ret = btrfs_dec_ref(trans, root, eb, 1);
+                        else
+                                ret = btrfs_dec_ref(trans, root, eb, 0);
+                        BUG_ON(ret);
+                }
+                /* make block locked assertion in clean_tree_block happy */
+                if (!path->locks[level] &&
+                    btrfs_header_generation(eb) == trans->transid) {
+                        btrfs_tree_lock(eb);
+                        btrfs_set_lock_blocking(eb);
+                        path->locks[level] = 1;
+                }
+                clean_tree_block(trans, root, eb);
         }
-out:
-        if (path->nodes[*level] == root->node)
-                parent = path->nodes[*level];
-        else
-                parent = path->nodes[*level + 1];
-        bytenr = path->nodes[*level]->start;
-        blocksize = path->nodes[*level]->len;
 
-        ret = btrfs_free_extent(trans, root, bytenr, blocksize, parent->start,
-                                btrfs_header_owner(parent), *level, 0);
+        if (eb == root->node) {
+                if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
+                        parent = eb->start;
+                else
+                        BUG_ON(root->root_key.objectid !=
+                               btrfs_header_owner(eb));
+        } else {
+                if (wc->flags[level + 1] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
+                        parent = path->nodes[level + 1]->start;
+                else
+                        BUG_ON(root->root_key.objectid !=
+                               btrfs_header_owner(path->nodes[level + 1]));
+        }
+
+        ret = btrfs_free_extent(trans, root, eb->start, eb->len, parent,
+                                root->root_key.objectid, level, 0);
         BUG_ON(ret);
+out:
+        wc->refs[level] = 0;
+        wc->flags[level] = 0;
+        return ret;
+}
+
+static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
+                                   struct btrfs_root *root,
+                                   struct btrfs_path *path,
+                                   struct walk_control *wc)
+{
+        struct extent_buffer *next;
+        struct extent_buffer *cur;
+        u64 bytenr;
+        u64 ptr_gen;
+        u32 blocksize;
+        int level = wc->level;
+        int ret;
+
+        while (level >= 0) {
+                cur = path->nodes[level];
+                BUG_ON(path->slots[level] >= btrfs_header_nritems(cur));
+
+                ret = walk_down_proc(trans, root, path, wc);
+                if (ret > 0)
+                        break;
+
+                if (level == 0)
+                        break;
+
+                bytenr = btrfs_node_blockptr(cur, path->slots[level]);
+                blocksize = btrfs_level_size(root, level - 1);
+                ptr_gen = btrfs_node_ptr_generation(cur, path->slots[level]);
+
+                next = read_tree_block(root, bytenr, blocksize, ptr_gen);
+                btrfs_tree_lock(next);
+                btrfs_set_lock_blocking(next);
 
-        if (path->locks[*level]) {
-                btrfs_tree_unlock(path->nodes[*level]);
-                path->locks[*level] = 0;
+                level--;
+                BUG_ON(level != btrfs_header_level(next));
+                path->nodes[level] = next;
+                path->slots[level] = 0;
+                path->locks[level] = 1;
+                wc->level = level;
         }
-        free_extent_buffer(path->nodes[*level]);
-        path->nodes[*level] = NULL;
-        *level += 1;
-        cond_resched();
         return 0;
 }
 
-/*
- * helper for dropping snapshots.  This walks back up the tree in the path
- * to find the first node higher up where we haven't yet gone through
- * all the slots
- */
 static noinline int walk_up_tree(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root,
                                  struct btrfs_path *path,
-                                 int *level, int max_level)
+                                 struct walk_control *wc, int max_level)
 {
-        struct btrfs_root_item *root_item = &root->root_item;
-        int i;
-        int slot;
+        int level = wc->level;
         int ret;
 
-        for (i = *level; i < max_level && path->nodes[i]; i++) {
-                slot = path->slots[i];
-                if (slot + 1 < btrfs_header_nritems(path->nodes[i])) {
-                        /*
-                         * there is more work to do in this level.
-                         * Update the drop_progress marker to reflect
-                         * the work we've done so far, and then bump
-                         * the slot number
-                         */
-                        path->slots[i]++;
-                        WARN_ON(*level == 0);
-                        if (max_level == BTRFS_MAX_LEVEL) {
-                                btrfs_node_key(path->nodes[i],
-                                               &root_item->drop_progress,
-                                               path->slots[i]);
-                                root_item->drop_level = i;
-                        }
-                        *level = i;
+        path->slots[level] = btrfs_header_nritems(path->nodes[level]);
+        while (level < max_level && path->nodes[level]) {
+                wc->level = level;
+                if (path->slots[level] + 1 <
+                    btrfs_header_nritems(path->nodes[level])) {
+                        path->slots[level]++;
                         return 0;
                 } else {
-                        struct extent_buffer *parent;
-
-                        /*
-                         * this whole node is done, free our reference
-                         * on it and go up one level
-                         */
-                        if (path->nodes[*level] == root->node)
-                                parent = path->nodes[*level];
-                        else
-                                parent = path->nodes[*level + 1];
+                        ret = walk_up_proc(trans, root, path, wc);
+                        if (ret > 0)
+                                return 0;
 
-                        clean_tree_block(trans, root, path->nodes[i]);
-                        ret = btrfs_free_extent(trans, root,
-                                                path->nodes[i]->start,
-                                                path->nodes[i]->len,
-                                                parent->start,
-                                                btrfs_header_owner(parent),
-                                                *level, 0);
-                        BUG_ON(ret);
-                        if (path->locks[*level]) {
-                                btrfs_tree_unlock(path->nodes[i]);
-                                path->locks[i] = 0;
+                        if (path->locks[level]) {
+                                btrfs_tree_unlock(path->nodes[level]);
+                                path->locks[level] = 0;
                         }
-                        free_extent_buffer(path->nodes[i]);
-                        path->nodes[i] = NULL;
-                        *level = i + 1;
+                        free_extent_buffer(path->nodes[level]);
+                        path->nodes[level] = NULL;
+                        level++;
                 }
         }
         return 1;
 }
 
 /*
- * drop the reference count on the tree rooted at 'snap'.  This traverses
- * the tree freeing any blocks that have a ref count of zero after being
- * decremented.
+ * drop a subvolume tree.
+ *
+ * this function traverses the tree freeing any blocks that only
+ * referenced by the tree.
+ *
+ * when a shared tree block is found. this function decreases its
+ * reference count by one. if update_ref is true, this function
+ * also make sure backrefs for the shared block and all lower level
+ * blocks are properly updated.
  */
-int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
-                        *root)
+int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref)
 {
-        int ret = 0;
-        int wret;
-        int level;
         struct btrfs_path *path;
-        int update_count;
+        struct btrfs_trans_handle *trans;
+        struct btrfs_root *tree_root = root->fs_info->tree_root;
         struct btrfs_root_item *root_item = &root->root_item;
+        struct walk_control *wc;
+        struct btrfs_key key;
+        int err = 0;
+        int ret;
+        int level;
 
         path = btrfs_alloc_path();
         BUG_ON(!path);
 
-        level = btrfs_header_level(root->node);
+        wc = kzalloc(sizeof(*wc), GFP_NOFS);
+        BUG_ON(!wc);
+
+        trans = btrfs_start_transaction(tree_root, 1);
+
         if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
+                level = btrfs_header_level(root->node);
                 path->nodes[level] = btrfs_lock_root_node(root);
                 btrfs_set_lock_blocking(path->nodes[level]);
                 path->slots[level] = 0;
                 path->locks[level] = 1;
+                memset(&wc->update_progress, 0,
+                       sizeof(wc->update_progress));
         } else {
-                struct btrfs_key key;
-                struct btrfs_disk_key found_key;
-                struct extent_buffer *node;
-
                 btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);
+                memcpy(&wc->update_progress, &key,
+                       sizeof(wc->update_progress));
+
                 level = root_item->drop_level;
+                BUG_ON(level == 0);
                 path->lowest_level = level;
-                wret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
-                if (wret < 0) {
-                        ret = wret;
+                ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+                path->lowest_level = 0;
+                if (ret < 0) {
+                        err = ret;
                         goto out;
                 }
-                node = path->nodes[level];
-                btrfs_node_key(node, &found_key, path->slots[level]);
-                WARN_ON(memcmp(&found_key, &root_item->drop_progress,
-                               sizeof(found_key)));
+                btrfs_node_key_to_cpu(path->nodes[level], &key,
+                                      path->slots[level]);
+                WARN_ON(memcmp(&key, &wc->update_progress, sizeof(key)));
+
                 /*
                  * unlock our path, this is safe because only this
                  * function is allowed to delete this snapshot
                  */
                 btrfs_unlock_up_safe(path, 0);
+
+                level = btrfs_header_level(root->node);
+                while (1) {
+                        btrfs_tree_lock(path->nodes[level]);
+                        btrfs_set_lock_blocking(path->nodes[level]);
+
+                        ret = btrfs_lookup_extent_info(trans, root,
+                                                path->nodes[level]->start,
+                                                path->nodes[level]->len,
+                                                &wc->refs[level],
+                                                &wc->flags[level]);
+                        BUG_ON(ret);
+                        BUG_ON(wc->refs[level] == 0);
+
+                        if (level == root_item->drop_level)
+                                break;
+
+                        btrfs_tree_unlock(path->nodes[level]);
+                        WARN_ON(wc->refs[level] != 1);
+                        level--;
+                }
         }
+
+        wc->level = level;
+        wc->shared_level = -1;
+        wc->stage = DROP_REFERENCE;
+        wc->update_ref = update_ref;
+        wc->keep_locks = 0;
+
         while (1) {
-                unsigned long update;
-                wret = walk_down_tree(trans, root, path, &level);
-                if (wret > 0)
+                ret = walk_down_tree(trans, root, path, wc);
+                if (ret < 0) {
+                        err = ret;
                         break;
-                if (wret < 0)
-                        ret = wret;
+                }
 
-                wret = walk_up_tree(trans, root, path, &level,
-                                    BTRFS_MAX_LEVEL);
-                if (wret > 0)
+                ret = walk_up_tree(trans, root, path, wc, BTRFS_MAX_LEVEL);
+                if (ret < 0) {
+                        err = ret;
                         break;
-                if (wret < 0)
-                        ret = wret;
-                if (trans->transaction->in_commit ||
-                    trans->transaction->delayed_refs.flushing) {
-                        ret = -EAGAIN;
+                }
+
+                if (ret > 0) {
+                        BUG_ON(wc->stage != DROP_REFERENCE);
                         break;
                 }
-                for (update_count = 0; update_count < 16; update_count++) {
+
+                if (wc->stage == DROP_REFERENCE) {
+                        level = wc->level;
+                        btrfs_node_key(path->nodes[level],
+                                       &root_item->drop_progress,
+                                       path->slots[level]);
+                        root_item->drop_level = level;
+                }
+
+                BUG_ON(wc->level == 0);
+                if (trans->transaction->in_commit ||
+                    trans->transaction->delayed_refs.flushing) {
+                        ret = btrfs_update_root(trans, tree_root,
+                                                &root->root_key,
+                                                root_item);
+                        BUG_ON(ret);
+
+                        btrfs_end_transaction(trans, tree_root);
+                        trans = btrfs_start_transaction(tree_root, 1);
+                } else {
+                        unsigned long update;
                         update = trans->delayed_ref_updates;
                         trans->delayed_ref_updates = 0;
                         if (update)
-                                btrfs_run_delayed_refs(trans, root, update);
-                        else
-                                break;
+                                btrfs_run_delayed_refs(trans, tree_root,
+                                                       update);
                 }
         }
+        btrfs_release_path(root, path);
+        BUG_ON(err);
+
+        ret = btrfs_del_root(trans, tree_root, &root->root_key);
+        BUG_ON(ret);
+
+        free_extent_buffer(root->node);
+        free_extent_buffer(root->commit_root);
+        kfree(root);
 out:
+        btrfs_end_transaction(trans, tree_root);
+        kfree(wc);
         btrfs_free_path(path);
-        return ret;
+        return err;
 }
 
+/*
+ * drop subtree rooted at tree block 'node'.
+ *
+ * NOTE: this function will unlock and release tree block 'node'
+ */
 int btrfs_drop_subtree(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root,
                         struct extent_buffer *node,
                         struct extent_buffer *parent)
 {
         struct btrfs_path *path;
+        struct walk_control *wc;
         int level;
         int parent_level;
         int ret = 0;
         int wret;
 
+        BUG_ON(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID);
+
         path = btrfs_alloc_path();
         BUG_ON(!path);
 
+        wc = kzalloc(sizeof(*wc), GFP_NOFS);
+        BUG_ON(!wc);
+
         btrfs_assert_tree_locked(parent);
         parent_level = btrfs_header_level(parent);
         extent_buffer_get(parent);
@@ -4817,24 +5243,33 @@ int btrfs_drop_subtree(struct btrfs_trans_handle *trans,
 
         btrfs_assert_tree_locked(node);
         level = btrfs_header_level(node);
-        extent_buffer_get(node);
         path->nodes[level] = node;
         path->slots[level] = 0;
+        path->locks[level] = 1;
+
+        wc->refs[parent_level] = 1;
+        wc->flags[parent_level] = BTRFS_BLOCK_FLAG_FULL_BACKREF;
+        wc->level = level;
+        wc->shared_level = -1;
+        wc->stage = DROP_REFERENCE;
+        wc->update_ref = 0;
+        wc->keep_locks = 1;
 
         while (1) {
-                wret = walk_down_tree(trans, root, path, &level);
-                if (wret < 0)
+                wret = walk_down_tree(trans, root, path, wc);
+                if (wret < 0) {
                         ret = wret;
-                if (wret != 0)
                         break;
+                }
 
-                wret = walk_up_tree(trans, root, path, &level, parent_level);
+                wret = walk_up_tree(trans, root, path, wc, parent_level);
                 if (wret < 0)
                         ret = wret;
                 if (wret != 0)
                         break;
         }
 
+        kfree(wc);
         btrfs_free_path(path);
         return ret;
 }
@@ -6739,11 +7174,16 @@ int btrfs_free_block_groups(struct btrfs_fs_info *info)
                          &info->block_group_cache_tree);
                 spin_unlock(&info->block_group_cache_lock);
 
-                btrfs_remove_free_space_cache(block_group);
                 down_write(&block_group->space_info->groups_sem);
                 list_del(&block_group->list);
                 up_write(&block_group->space_info->groups_sem);
 
+                if (block_group->cached == BTRFS_CACHE_STARTED)
+                        wait_event(block_group->caching_q,
+                                   block_group_cache_done(block_group));
+
+                btrfs_remove_free_space_cache(block_group);
+
                 WARN_ON(atomic_read(&block_group->count) != 1);
                 kfree(block_group);
 
@@ -6809,9 +7249,19 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                 atomic_set(&cache->count, 1);
                 spin_lock_init(&cache->lock);
                 spin_lock_init(&cache->tree_lock);
-                mutex_init(&cache->cache_mutex);
+                cache->fs_info = info;
+                init_waitqueue_head(&cache->caching_q);
                 INIT_LIST_HEAD(&cache->list);
                 INIT_LIST_HEAD(&cache->cluster_list);
+
+                /*
+                 * we only want to have 32k of ram per block group for keeping
+                 * track of free space, and if we pass 1/2 of that we want to
+                 * start converting things over to using bitmaps
+                 */
+                cache->extents_thresh = ((1024 * 32) / 2) /
+                        sizeof(struct btrfs_free_space);
+
                 read_extent_buffer(leaf, &cache->item,
                                    btrfs_item_ptr_offset(leaf, path->slots[0]),
                                    sizeof(cache->item));
@@ -6820,6 +7270,26 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                 key.objectid = found_key.objectid + found_key.offset;
                 btrfs_release_path(root, path);
                 cache->flags = btrfs_block_group_flags(&cache->item);
+                cache->sectorsize = root->sectorsize;
+
+                remove_sb_from_cache(root, cache);
+
+                /*
+                 * check for two cases, either we are full, and therefore
+                 * don't need to bother with the caching work since we won't
+                 * find any space, or we are empty, and we can just add all
+                 * the space in and be done with it.  This saves us _alot_ of
+                 * time, particularly in the full case.
+                 */
+                if (found_key.offset == btrfs_block_group_used(&cache->item)) {
+                        cache->cached = BTRFS_CACHE_FINISHED;
+                } else if (btrfs_block_group_used(&cache->item) == 0) {
+                        cache->cached = BTRFS_CACHE_FINISHED;
+                        add_new_free_space(cache, root->fs_info,
+                                           found_key.objectid,
+                                           found_key.objectid +
+                                           found_key.offset);
+                }
 
                 ret = update_space_info(info, cache->flags, found_key.offset,
                                         btrfs_block_group_used(&cache->item),
@@ -6863,10 +7333,19 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
         cache->key.objectid = chunk_offset;
         cache->key.offset = size;
         cache->key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
+        cache->sectorsize = root->sectorsize;
+
+        /*
+         * we only want to have 32k of ram per block group for keeping track
+         * of free space, and if we pass 1/2 of that we want to start
+         * converting things over to using bitmaps
+         */
+        cache->extents_thresh = ((1024 * 32) / 2) /
+                sizeof(struct btrfs_free_space);
         atomic_set(&cache->count, 1);
         spin_lock_init(&cache->lock);
         spin_lock_init(&cache->tree_lock);
-        mutex_init(&cache->cache_mutex);
+        init_waitqueue_head(&cache->caching_q);
         INIT_LIST_HEAD(&cache->list);
         INIT_LIST_HEAD(&cache->cluster_list);
 
@@ -6875,6 +7354,12 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
         cache->flags = type;
         btrfs_set_block_group_flags(&cache->item, type);
 
+        cache->cached = BTRFS_CACHE_FINISHED;
+        remove_sb_from_cache(root, cache);
+
+        add_new_free_space(cache, root->fs_info, chunk_offset,
+                           chunk_offset + size);
+
         ret = update_space_info(root->fs_info, cache->flags, size, bytes_used,
                                 &cache->space_info);
         BUG_ON(ret);
@@ -6933,7 +7418,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
         rb_erase(&block_group->cache_node,
                  &root->fs_info->block_group_cache_tree);
         spin_unlock(&root->fs_info->block_group_cache_lock);
-        btrfs_remove_free_space_cache(block_group);
+
         down_write(&block_group->space_info->groups_sem);
         /*
          * we must use list_del_init so people can check to see if they
@@ -6942,11 +7427,18 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
         list_del_init(&block_group->list);
         up_write(&block_group->space_info->groups_sem);
 
+        if (block_group->cached == BTRFS_CACHE_STARTED)
+                wait_event(block_group->caching_q,
+                           block_group_cache_done(block_group));
+
+        btrfs_remove_free_space_cache(block_group);
+
         spin_lock(&block_group->space_info->lock);
         block_group->space_info->total_bytes -= block_group->key.offset;
         block_group->space_info->bytes_readonly -= block_group->key.offset;
         spin_unlock(&block_group->space_info->lock);
-        block_group->space_info->full = 0;
+
+        btrfs_clear_space_info_full(root->fs_info);
 
         btrfs_put_block_group(block_group);
         btrfs_put_block_group(block_group);