__le64 device_id;
 } __attribute__ ((__packed__));
 
+/* tag for the radix tree of block groups in ram */
+#define BTRFS_BLOCK_GROUP_DIRTY 0
+#define BTRFS_BLOCK_GROUP_HINTS 8
+#define BTRFS_BLOCK_GROUP_SIZE (256 * 1024 * 1024)
+struct btrfs_block_group_item {
+       __le64 used;
+} __attribute__ ((__packed__));
+
+struct btrfs_block_group_cache {
+       struct btrfs_key key;
+       struct btrfs_block_group_item item;
+};
+
 struct crypto_hash;
 struct btrfs_fs_info {
        struct btrfs_root *extent_root;
        struct radix_tree_root pending_del_radix;
        struct radix_tree_root pinned_radix;
        struct radix_tree_root dev_radix;
+       struct radix_tree_root block_group_radix;
 
        u64 extent_tree_insert[BTRFS_MAX_LEVEL * 3];
        int extent_tree_insert_nr;
  * info about object characteristics.  There is one for every file and dir in
  * the FS
  */
-#define BTRFS_INODE_ITEM_KEY   1
+#define BTRFS_INODE_ITEM_KEY           1
+
+/* reserve 2-15 close to the inode for later flexibility */
 
 /*
  * dir items are the name -> inode pointers in a directory.  There is one
  * for every name in a directory.
  */
-#define BTRFS_DIR_ITEM_KEY     2
-#define BTRFS_DIR_INDEX_KEY    3
+#define BTRFS_DIR_ITEM_KEY     16
+#define BTRFS_DIR_INDEX_KEY    17
 /*
- * inline data is file data that fits in the btree.
+ * extent data is for file data
  */
-#define BTRFS_INLINE_DATA_KEY  4
-/*
- * extent data is for data that can't fit in the btree.  It points to
- * a (hopefully) huge chunk of disk
- */
-#define BTRFS_EXTENT_DATA_KEY  5
+#define BTRFS_EXTENT_DATA_KEY  18
 /*
  * csum items have the checksums for data in the extents
  */
-#define BTRFS_CSUM_ITEM_KEY    6
+#define BTRFS_CSUM_ITEM_KEY    19
+
+/* reserve 20-31 for other file stuff */
 
 /*
  * root items point to tree roots.  There are typically in the root
  * tree used by the super block to find all the other trees
  */
-#define BTRFS_ROOT_ITEM_KEY    7
+#define BTRFS_ROOT_ITEM_KEY    32
 /*
  * extent items are in the extent map tree.  These record which blocks
  * are used, and how many references there are to each block
  */
-#define BTRFS_EXTENT_ITEM_KEY  8
+#define BTRFS_EXTENT_ITEM_KEY  33
+
+/*
+ * block groups give us hints into the extent allocation trees.  Which
+ * blocks are free etc etc
+ */
+#define BTRFS_BLOCK_GROUP_ITEM_KEY 34
 
 /*
  * dev items list the devices that make up the FS
  */
-#define BTRFS_DEV_ITEM_KEY     9
+#define BTRFS_DEV_ITEM_KEY     35
 
 /*
  * string items are for debugging.  They just store a short string of
  * data in the FS
  */
-#define BTRFS_STRING_ITEM_KEY  10
+#define BTRFS_STRING_ITEM_KEY  253
+
+
+static inline u64 btrfs_block_group_used(struct btrfs_block_group_item *bi)
+{
+       return le64_to_cpu(bi->used);
+}
+
+static inline void btrfs_set_block_group_used(struct
+                                                  btrfs_block_group_item *bi,
+                                                  u64 val)
+{
+       bi->used = cpu_to_le64(val);
+}
 
 static inline u64 btrfs_inode_generation(struct btrfs_inode_item *i)
 {
 int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root,
                                u64 blocknr, u64 num_blocks);
+int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
+                                   struct btrfs_root *root);
+int btrfs_free_block_groups(struct btrfs_fs_info *info);
+int btrfs_read_block_groups(struct btrfs_root *root);
 /* ctree.c */
 int btrfs_extend_item(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_path *path, u32 data_size);
 
        return 0;
 }
 
+static int write_one_cache_group(struct btrfs_trans_handle *trans,
+                                struct btrfs_root *root,
+                                struct btrfs_path *path,
+                                struct btrfs_block_group_cache *cache)
+{
+       int ret;
+       int pending_ret;
+       struct btrfs_root *extent_root = root->fs_info->extent_root;
+       struct btrfs_block_group_item *bi;
+       struct btrfs_key ins;
+
+       find_free_extent(trans, extent_root, 0, 0, (u64)-1, &ins);
+       ret = btrfs_search_slot(trans, extent_root, &cache->key, path, 0, 1);
+       BUG_ON(ret);
+       bi = btrfs_item_ptr(btrfs_buffer_leaf(path->nodes[0]), path->slots[0],
+                           struct btrfs_block_group_item);
+       memcpy(bi, &cache->item, sizeof(*bi));
+       mark_buffer_dirty(path->nodes[0]);
+       btrfs_release_path(extent_root, path);
+
+       finish_current_insert(trans, extent_root);
+       pending_ret = del_pending_extents(trans, extent_root);
+       if (ret)
+               return ret;
+       if (pending_ret)
+               return pending_ret;
+       return 0;
+
+}
+
+int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
+                                   struct btrfs_root *root)
+{
+       struct btrfs_block_group_cache *cache[8];
+       int ret;
+       int err = 0;
+       int werr = 0;
+       struct radix_tree_root *radix = &root->fs_info->block_group_radix;
+       int i;
+       struct btrfs_path *path;
+
+       path = btrfs_alloc_path();
+       if (!path)
+               return -ENOMEM;
+
+       while(1) {
+               ret = radix_tree_gang_lookup_tag(radix, (void **)cache,
+                                                0, ARRAY_SIZE(cache),
+                                                BTRFS_BLOCK_GROUP_DIRTY);
+               if (!ret)
+                       break;
+               for (i = 0; i < ret; i++) {
+                       radix_tree_tag_clear(radix, cache[i]->key.objectid +
+                                            cache[i]->key.offset - 1,
+                                            BTRFS_BLOCK_GROUP_DIRTY);
+                       err = write_one_cache_group(trans, root,
+                                                   path, cache[i]);
+                       if (err)
+                               werr = err;
+               }
+       }
+       btrfs_free_path(path);
+       return werr;
+}
+
+static int update_block_group(struct btrfs_trans_handle *trans,
+                             struct btrfs_root *root,
+                             u64 blocknr, u64 num, int alloc)
+{
+       struct btrfs_block_group_cache *cache;
+       struct btrfs_fs_info *info = root->fs_info;
+       u64 total = num;
+       u64 old_val;
+       u64 block_in_group;
+       int ret;
+       while(total) {
+               ret = radix_tree_gang_lookup(&info->block_group_radix,
+                                            (void **)&cache, blocknr, 1);
+               if (!ret)
+                       return -1;
+               block_in_group = blocknr - cache->key.objectid;
+               WARN_ON(block_in_group > cache->key.offset);
+               radix_tree_tag_set(&info->block_group_radix,
+                                  cache->key.objectid + cache->key.offset - 1,
+                                  BTRFS_BLOCK_GROUP_DIRTY);
+
+               old_val = btrfs_block_group_used(&cache->item);
+               num = min(total, cache->key.offset - block_in_group);
+               total -= num;
+               blocknr += num;
+               if (alloc)
+                       old_val += num;
+               else
+                       old_val -= num;
+               btrfs_set_block_group_used(&cache->item, old_val);
+       }
+       return 0;
+}
+
 int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans, struct
                               btrfs_root *root)
 {
                ret = btrfs_del_item(trans, extent_root, path);
                if (ret)
                        BUG();
+               ret = update_block_group(trans, root, blocknr, num_blocks, 0);
+               BUG_ON(ret);
        }
        btrfs_release_path(extent_root, path);
        btrfs_free_path(path);
                num_blocks = 1;
                total_needed = min(level + 2, BTRFS_MAX_LEVEL) * 3;
        }
-       if (info->last_insert.objectid == 0 && search_end == (u64)-1) {
-               struct btrfs_disk_key *last_key;
-               btrfs_init_path(path);
-               ins->objectid = (u64)-1;
-               ins->offset = (u64)-1;
-               ret = btrfs_search_slot(trans, root, ins, path, 0, 0);
-               if (ret < 0)
-                       goto error;
-               BUG_ON(ret == 0);
-               if (path->slots[0] > 0)
-                       path->slots[0]--;
-               l = btrfs_buffer_leaf(path->nodes[0]);
-               last_key = &l->items[path->slots[0]].key;
-               search_start = btrfs_disk_key_objectid(last_key);
-       }
        if (info->last_insert.objectid > search_start)
                search_start = info->last_insert.objectid;
 
                        goto check_pending;
                }
                btrfs_disk_key_to_cpu(&key, &l->items[slot].key);
+               if (btrfs_key_type(&key) != BTRFS_EXTENT_ITEM_KEY)
+                       goto next;
                if (key.objectid >= search_start) {
                        if (start_found) {
                                if (last_block < search_start)
                }
                start_found = 1;
                last_block = key.objectid + key.offset;
+next:
                path->slots[0]++;
        }
        // FIXME -ENOSPC
        btrfs_free_path(path);
        return ret;
 }
-
 /*
  * finds a free extent and does all the dirty work required for allocation
  * returns the key for the extent through ins, and a tree buffer for
                ins->objectid = info->extent_tree_prealloc[nr];
                info->extent_tree_insert[info->extent_tree_insert_nr++] =
                        ins->objectid;
+               ret = update_block_group(trans, root,
+                                        ins->objectid, ins->offset, 1);
+               BUG_ON(ret);
                return 0;
        }
        /* do the real allocation */
                return ret;
        if (pending_ret)
                return pending_ret;
+       ret = update_block_group(trans, root, ins->objectid, ins->offset, 1);
        return 0;
 }
 
                BUG();
                return NULL;
        }
+       BUG_ON(ret);
        buf = btrfs_find_create_tree_block(root, ins.objectid);
        set_buffer_uptodate(buf);
        return buf;
        btrfs_free_path(path);
        return ret;
 }
+
+int btrfs_free_block_groups(struct btrfs_fs_info *info)
+{
+       int ret;
+       struct btrfs_block_group_cache *cache[8];
+       int i;
+
+       while(1) {
+               ret = radix_tree_gang_lookup(&info->block_group_radix,
+                                            (void **)cache, 0,
+                                            ARRAY_SIZE(cache));
+               if (!ret)
+                       break;
+               for (i = 0; i < ret; i++) {
+                       radix_tree_delete(&info->block_group_radix,
+                                         cache[i]->key.objectid +
+                                         cache[i]->key.offset - 1);
+                       kfree(cache[i]);
+               }
+       }
+       return 0;
+}
+
+int btrfs_read_block_groups(struct btrfs_root *root)
+{
+       struct btrfs_path *path;
+       int ret;
+       int err = 0;
+       struct btrfs_block_group_item *bi;
+       struct btrfs_block_group_cache *cache;
+       struct btrfs_key key;
+       struct btrfs_key found_key;
+       struct btrfs_leaf *leaf;
+       u64 group_size_blocks = BTRFS_BLOCK_GROUP_SIZE / root->blocksize;
+
+       root = root->fs_info->extent_root;
+       key.objectid = 0;
+       key.offset = group_size_blocks;
+       key.flags = 0;
+       btrfs_set_key_type(&key, BTRFS_BLOCK_GROUP_ITEM_KEY);
+
+       path = btrfs_alloc_path();
+       if (!path)
+               return -ENOMEM;
+
+       while(1) {
+               ret = btrfs_search_slot(NULL, root->fs_info->extent_root,
+                                       &key, path, 0, 0);
+               if (ret != 0) {
+                       err = ret;
+                       break;
+               }
+               leaf = btrfs_buffer_leaf(path->nodes[0]);
+               btrfs_disk_key_to_cpu(&found_key,
+                                     &leaf->items[path->slots[0]].key);
+               cache = kmalloc(sizeof(*cache), GFP_NOFS);
+               if (!cache) {
+                       err = -1;
+                       break;
+               }
+               bi = btrfs_item_ptr(leaf, path->slots[0],
+                                   struct btrfs_block_group_item);
+               memcpy(&cache->item, bi, sizeof(*bi));
+               memcpy(&cache->key, &found_key, sizeof(found_key));
+               key.objectid = found_key.objectid + found_key.offset;
+               btrfs_release_path(root, path);
+               ret = radix_tree_insert(&root->fs_info->block_group_radix,
+                                       found_key.objectid +
+                                       found_key.offset - 1,
+                                       (void *)cache);
+               BUG_ON(ret);
+               if (key.objectid >=
+                   btrfs_super_total_blocks(root->fs_info->disk_super))
+                       break;
+       }
+
+       btrfs_free_path(path);
+       return 0;
+}