1 files changed, 794 insertions, 302 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index edc7d20..72a2b9c 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);