Btrfs: Make free space cache code generic

So we can re-use the code to cache free inode numbers.

The change is quite straightforward. Two new structures are introduced.

- struct btrfs_free_space_ctl

  We move those variables that are used for caching free space from
  struct btrfs_block_group_cache to this new struct.

- struct btrfs_free_space_op

  We do block group specific work (e.g. calculation of extents threshold)
  through functions registered in this struct.

And then we can remove references to struct btrfs_block_group_cache.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

4 files changed, 271 insertions, 223 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 2e61fe1b6b8c..d17e4a3b8bf7 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -830,9 +830,6 @@ struct btrfs_block_group_cache {
         u64 bytes_super;
         u64 flags;
         u64 sectorsize;
-        int extents_thresh;
-        int free_extents;
-        int total_bitmaps;
         unsigned int ro:1;
         unsigned int dirty:1;
         unsigned int iref:1;
@@ -847,9 +844,7 @@ struct btrfs_block_group_cache {
         struct btrfs_space_info *space_info;
 
         /* free space cache stuff */
-        spinlock_t tree_lock;
-        struct rb_root free_space_offset;
-        u64 free_space;
+        struct btrfs_free_space_ctl *free_space_ctl;
 
         /* block group cache stuff */
         struct rb_node cache_node;
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 31f33ba56fe8..904eae10ec65 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -105,6 +105,7 @@ void btrfs_put_block_group(struct btrfs_block_group_cache *cache)
                 WARN_ON(cache->pinned > 0);
                 WARN_ON(cache->reserved > 0);
                 WARN_ON(cache->reserved_pinned > 0);
+                kfree(cache->free_space_ctl);
                 kfree(cache);
         }
 }
@@ -4893,7 +4894,7 @@ wait_block_group_cache_progress(struct btrfs_block_group_cache *cache,
                 return 0;
 
         wait_event(caching_ctl->wait, block_group_cache_done(cache) ||
-                   (cache->free_space >= num_bytes));
+                   (cache->free_space_ctl->free_space >= num_bytes));
 
         put_caching_control(caching_ctl);
         return 0;
@@ -8551,10 +8552,16 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                         ret = -ENOMEM;
                         goto error;
                 }
+                cache->free_space_ctl = kzalloc(sizeof(*cache->free_space_ctl),
+                                                GFP_NOFS);
+                if (!cache->free_space_ctl) {
+                        kfree(cache);
+                        ret = -ENOMEM;
+                        goto error;
+                }
 
                 atomic_set(&cache->count, 1);
                 spin_lock_init(&cache->lock);
-                spin_lock_init(&cache->tree_lock);
                 cache->fs_info = info;
                 INIT_LIST_HEAD(&cache->list);
                 INIT_LIST_HEAD(&cache->cluster_list);
@@ -8562,14 +8569,6 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                 if (need_clear)
                         cache->disk_cache_state = BTRFS_DC_CLEAR;
 
-                /*
-                 * 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));
@@ -8580,6 +8579,8 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                 cache->flags = btrfs_block_group_flags(&cache->item);
                 cache->sectorsize = root->sectorsize;
 
+                btrfs_init_free_space_ctl(cache);
+
                 /*
                  * We need to exclude the super stripes now so that the space
                  * info has super bytes accounted for, otherwise we'll think
@@ -8666,6 +8667,12 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
         cache = kzalloc(sizeof(*cache), GFP_NOFS);
         if (!cache)
                 return -ENOMEM;
+        cache->free_space_ctl = kzalloc(sizeof(*cache->free_space_ctl),
+                                        GFP_NOFS);
+        if (!cache->free_space_ctl) {
+                kfree(cache);
+                return -ENOMEM;
+        }
 
         cache->key.objectid = chunk_offset;
         cache->key.offset = size;
@@ -8673,19 +8680,13 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
         cache->sectorsize = root->sectorsize;
         cache->fs_info = root->fs_info;
 
-        /*
-         * 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);
         INIT_LIST_HEAD(&cache->list);
         INIT_LIST_HEAD(&cache->cluster_list);
 
+        btrfs_init_free_space_ctl(cache);
+
         btrfs_set_block_group_used(&cache->item, bytes_used);
         btrfs_set_block_group_chunk_objectid(&cache->item, chunk_objectid);
         cache->flags = type;
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 0e23bbabbba2..d4fb4f077a79 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -29,9 +29,7 @@
 #define BITS_PER_BITMAP         (PAGE_CACHE_SIZE * 8)
 #define MAX_CACHE_BYTES_PER_GIG (32 * 1024)
 
-static void recalculate_thresholds(struct btrfs_block_group_cache
-                                   *block_group);
-static int link_free_space(struct btrfs_block_group_cache *block_group,
+static int link_free_space(struct btrfs_free_space_ctl *ctl,
                            struct btrfs_free_space *info);
 
 struct inode *lookup_free_space_inode(struct btrfs_root *root,
@@ -212,6 +210,7 @@ static int readahead_cache(struct inode *inode)
 int load_free_space_cache(struct btrfs_fs_info *fs_info,
                           struct btrfs_block_group_cache *block_group)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_root *root = fs_info->tree_root;
         struct inode *inode;
         struct btrfs_free_space_header *header;
@@ -417,9 +416,9 @@ int load_free_space_cache(struct btrfs_fs_info *fs_info,
                         }
 
                         if (entry->type == BTRFS_FREE_SPACE_EXTENT) {
-                                spin_lock(&block_group->tree_lock);
-                                ret = link_free_space(block_group, e);
-                                spin_unlock(&block_group->tree_lock);
+                                spin_lock(&ctl->tree_lock);
+                                ret = link_free_space(ctl, e);
+                                spin_unlock(&ctl->tree_lock);
                                 BUG_ON(ret);
                         } else {
                                 e->bitmap = kzalloc(PAGE_CACHE_SIZE, GFP_NOFS);
@@ -431,11 +430,11 @@ int load_free_space_cache(struct btrfs_fs_info *fs_info,
                                         page_cache_release(page);
                                         goto free_cache;
                                 }
-                                spin_lock(&block_group->tree_lock);
-                                ret = link_free_space(block_group, e);
-                                block_group->total_bitmaps++;
-                                recalculate_thresholds(block_group);
-                                spin_unlock(&block_group->tree_lock);
+                                spin_lock(&ctl->tree_lock);
+                                ret = link_free_space(ctl, e);
+                                ctl->total_bitmaps++;
+                                ctl->op->recalc_thresholds(ctl);
+                                spin_unlock(&ctl->tree_lock);
                                 list_add_tail(&e->list, &bitmaps);
                         }
 
@@ -471,16 +470,16 @@ next:
                 index++;
         }
 
-        spin_lock(&block_group->tree_lock);
-        if (block_group->free_space != (block_group->key.offset - used -
-                                        block_group->bytes_super)) {
-                spin_unlock(&block_group->tree_lock);
+        spin_lock(&ctl->tree_lock);
+        if (ctl->free_space != (block_group->key.offset - used -
+                                block_group->bytes_super)) {
+                spin_unlock(&ctl->tree_lock);
                 printk(KERN_ERR "block group %llu has an wrong amount of free "
                        "space\n", block_group->key.objectid);
                 ret = 0;
                 goto free_cache;
         }
-        spin_unlock(&block_group->tree_lock);
+        spin_unlock(&ctl->tree_lock);
 
         ret = 1;
 out:
@@ -503,6 +502,7 @@ int btrfs_write_out_cache(struct btrfs_root *root,
                           struct btrfs_block_group_cache *block_group,
                           struct btrfs_path *path)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space_header *header;
         struct extent_buffer *leaf;
         struct inode *inode;
@@ -546,7 +546,7 @@ int btrfs_write_out_cache(struct btrfs_root *root,
                 return 0;
         }
 
-        node = rb_first(&block_group->free_space_offset);
+        node = rb_first(&ctl->free_space_offset);
         if (!node) {
                 iput(inode);
                 return 0;
@@ -851,30 +851,30 @@ out_free:
         return ret;
 }
 
-static inline unsigned long offset_to_bit(u64 bitmap_start, u64 sectorsize,
+static inline unsigned long offset_to_bit(u64 bitmap_start, u32 unit,
                                           u64 offset)
 {
         BUG_ON(offset < bitmap_start);
         offset -= bitmap_start;
-        return (unsigned long)(div64_u64(offset, sectorsize));
+        return (unsigned long)(div_u64(offset, unit));
 }
 
-static inline unsigned long bytes_to_bits(u64 bytes, u64 sectorsize)
+static inline unsigned long bytes_to_bits(u64 bytes, u32 unit)
 {
-        return (unsigned long)(div64_u64(bytes, sectorsize));
+        return (unsigned long)(div_u64(bytes, unit));
 }
 
-static inline u64 offset_to_bitmap(struct btrfs_block_group_cache *block_group,
+static inline u64 offset_to_bitmap(struct btrfs_free_space_ctl *ctl,
                                    u64 offset)
 {
         u64 bitmap_start;
         u64 bytes_per_bitmap;
 
-        bytes_per_bitmap = BITS_PER_BITMAP * block_group->sectorsize;
-        bitmap_start = offset - block_group->key.objectid;
+        bytes_per_bitmap = BITS_PER_BITMAP * ctl->unit;
+        bitmap_start = offset - ctl->start;
         bitmap_start = div64_u64(bitmap_start, bytes_per_bitmap);
         bitmap_start *= bytes_per_bitmap;
-        bitmap_start += block_group->key.objectid;
+        bitmap_start += ctl->start;
 
         return bitmap_start;
 }
@@ -932,10 +932,10 @@ static int tree_insert_offset(struct rb_root *root, u64 offset,
  * offset.
  */
 static struct btrfs_free_space *
-tree_search_offset(struct btrfs_block_group_cache *block_group,
+tree_search_offset(struct btrfs_free_space_ctl *ctl,
                    u64 offset, int bitmap_only, int fuzzy)
 {
-        struct rb_node *n = block_group->free_space_offset.rb_node;
+        struct rb_node *n = ctl->free_space_offset.rb_node;
         struct btrfs_free_space *entry, *prev = NULL;
 
         /* find entry that is closest to the 'offset' */
@@ -1031,8 +1031,7 @@ tree_search_offset(struct btrfs_block_group_cache *block_group,
                                 break;
                         }
                 }
-                if (entry->offset + BITS_PER_BITMAP *
-                    block_group->sectorsize > offset)
+                if (entry->offset + BITS_PER_BITMAP * ctl->unit > offset)
                         return entry;
         } else if (entry->offset + entry->bytes > offset)
                 return entry;
@@ -1043,7 +1042,7 @@ tree_search_offset(struct btrfs_block_group_cache *block_group,
         while (1) {
                 if (entry->bitmap) {
                         if (entry->offset + BITS_PER_BITMAP *
-                            block_group->sectorsize > offset)
+                            ctl->unit > offset)
                                 break;
                 } else {
                         if (entry->offset + entry->bytes > offset)
@@ -1059,42 +1058,47 @@ tree_search_offset(struct btrfs_block_group_cache *block_group,
 }
 
 static inline void
-__unlink_free_space(struct btrfs_block_group_cache *block_group,
+__unlink_free_space(struct btrfs_free_space_ctl *ctl,
                     struct btrfs_free_space *info)
 {
-        rb_erase(&info->offset_index, &block_group->free_space_offset);
-        block_group->free_extents--;
+        rb_erase(&info->offset_index, &ctl->free_space_offset);
+        ctl->free_extents--;
 }
 
-static void unlink_free_space(struct btrfs_block_group_cache *block_group,
+static void unlink_free_space(struct btrfs_free_space_ctl *ctl,
                               struct btrfs_free_space *info)
 {
-        __unlink_free_space(block_group, info);
-        block_group->free_space -= info->bytes;
+        __unlink_free_space(ctl, info);
+        ctl->free_space -= info->bytes;
 }
 
-static int link_free_space(struct btrfs_block_group_cache *block_group,
+static int link_free_space(struct btrfs_free_space_ctl *ctl,
                            struct btrfs_free_space *info)
 {
         int ret = 0;
 
         BUG_ON(!info->bitmap && !info->bytes);
-        ret = tree_insert_offset(&block_group->free_space_offset, info->offset,
+        ret = tree_insert_offset(&ctl->free_space_offset, info->offset,
                                  &info->offset_index, (info->bitmap != NULL));
         if (ret)
                 return ret;
 
-        block_group->free_space += info->bytes;
-        block_group->free_extents++;
+        ctl->free_space += info->bytes;
+        ctl->free_extents++;
         return ret;
 }
 
-static void recalculate_thresholds(struct btrfs_block_group_cache *block_group)
+static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
 {
+        struct btrfs_block_group_cache *block_group = ctl->private;
         u64 max_bytes;
         u64 bitmap_bytes;
         u64 extent_bytes;
         u64 size = block_group->key.offset;
+        u64 bytes_per_bg = BITS_PER_BITMAP * block_group->sectorsize;
+        int max_bitmaps = div64_u64(size + bytes_per_bg - 1, bytes_per_bg);
+
+        BUG_ON(ctl->total_bitmaps > max_bitmaps);
 
         /*
          * The goal is to keep the total amount of memory used per 1gb of space
@@ -1112,10 +1116,10 @@ static void recalculate_thresholds(struct btrfs_block_group_cache *block_group)
          * sure we don't go over our overall goal of MAX_CACHE_BYTES_PER_GIG as
          * we add more bitmaps.
          */
-        bitmap_bytes = (block_group->total_bitmaps + 1) * PAGE_CACHE_SIZE;
+        bitmap_bytes = (ctl->total_bitmaps + 1) * PAGE_CACHE_SIZE;
 
         if (bitmap_bytes >= max_bytes) {
-                block_group->extents_thresh = 0;
+                ctl->extents_thresh = 0;
                 return;
         }
 
@@ -1126,43 +1130,43 @@ static void recalculate_thresholds(struct btrfs_block_group_cache *block_group)
         extent_bytes = max_bytes - bitmap_bytes;
         extent_bytes = min_t(u64, extent_bytes, div64_u64(max_bytes, 2));
 
-        block_group->extents_thresh =
+        ctl->extents_thresh =
                 div64_u64(extent_bytes, (sizeof(struct btrfs_free_space)));
 }
 
-static void bitmap_clear_bits(struct btrfs_block_group_cache *block_group,
+static void bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
                               struct btrfs_free_space *info, u64 offset,
                               u64 bytes)
 {
         unsigned long start, count;
 
-        start = offset_to_bit(info->offset, block_group->sectorsize, offset);
-        count = bytes_to_bits(bytes, block_group->sectorsize);
+        start = offset_to_bit(info->offset, ctl->unit, offset);
+        count = bytes_to_bits(bytes, ctl->unit);
         BUG_ON(start + count > BITS_PER_BITMAP);
 
         bitmap_clear(info->bitmap, start, count);
 
         info->bytes -= bytes;
-        block_group->free_space -= bytes;
+        ctl->free_space -= bytes;
 }
 
-static void bitmap_set_bits(struct btrfs_block_group_cache *block_group,
+static void bitmap_set_bits(struct btrfs_free_space_ctl *ctl,
                             struct btrfs_free_space *info, u64 offset,
                             u64 bytes)
 {
         unsigned long start, count;
 
-        start = offset_to_bit(info->offset, block_group->sectorsize, offset);
-        count = bytes_to_bits(bytes, block_group->sectorsize);
+        start = offset_to_bit(info->offset, ctl->unit, offset);
+        count = bytes_to_bits(bytes, ctl->unit);
         BUG_ON(start + count > BITS_PER_BITMAP);
 
         bitmap_set(info->bitmap, start, count);
 
         info->bytes += bytes;
-        block_group->free_space += bytes;
+        ctl->free_space += bytes;
 }
 
-static int search_bitmap(struct btrfs_block_group_cache *block_group,
+static int search_bitmap(struct btrfs_free_space_ctl *ctl,
                          struct btrfs_free_space *bitmap_info, u64 *offset,
                          u64 *bytes)
 {
@@ -1170,9 +1174,9 @@ static int search_bitmap(struct btrfs_block_group_cache *block_group,
         unsigned long bits, i;
         unsigned long next_zero;
 
-        i = offset_to_bit(bitmap_info->offset, block_group->sectorsize,
+        i = offset_to_bit(bitmap_info->offset, ctl->unit,
                           max_t(u64, *offset, bitmap_info->offset));
-        bits = bytes_to_bits(*bytes, block_group->sectorsize);
+        bits = bytes_to_bits(*bytes, ctl->unit);
 
         for (i = find_next_bit(bitmap_info->bitmap, BITS_PER_BITMAP, i);
              i < BITS_PER_BITMAP;
@@ -1187,29 +1191,25 @@ static int search_bitmap(struct btrfs_block_group_cache *block_group,
         }
 
         if (found_bits) {
-                *offset = (u64)(i * block_group->sectorsize) +
-                        bitmap_info->offset;
-                *bytes = (u64)(found_bits) * block_group->sectorsize;
+                *offset = (u64)(i * ctl->unit) + bitmap_info->offset;
+                *bytes = (u64)(found_bits) * ctl->unit;
                 return 0;
         }
 
         return -1;
 }
 
-static struct btrfs_free_space *find_free_space(struct btrfs_block_group_cache
-                                                *block_group, u64 *offset,
-                                                u64 *bytes, int debug)
+static struct btrfs_free_space *
+find_free_space(struct btrfs_free_space_ctl *ctl, u64 *offset, u64 *bytes)
 {
         struct btrfs_free_space *entry;
         struct rb_node *node;
         int ret;
 
-        if (!block_group->free_space_offset.rb_node)
+        if (!ctl->free_space_offset.rb_node)
                 return NULL;
 
-        entry = tree_search_offset(block_group,
-                                   offset_to_bitmap(block_group, *offset),
-                                   0, 1);
+        entry = tree_search_offset(ctl, offset_to_bitmap(ctl, *offset), 0, 1);
         if (!entry)
                 return NULL;
 
@@ -1219,7 +1219,7 @@ static struct btrfs_free_space *find_free_space(struct btrfs_block_group_cache
                         continue;
 
                 if (entry->bitmap) {
-                        ret = search_bitmap(block_group, entry, offset, bytes);
+                        ret = search_bitmap(ctl, entry, offset, bytes);
                         if (!ret)
                                 return entry;
                         continue;
@@ -1233,33 +1233,28 @@ static struct btrfs_free_space *find_free_space(struct btrfs_block_group_cache
         return NULL;
 }
 
-static void add_new_bitmap(struct btrfs_block_group_cache *block_group,
+static void add_new_bitmap(struct btrfs_free_space_ctl *ctl,
                            struct btrfs_free_space *info, u64 offset)
 {
-        u64 bytes_per_bg = BITS_PER_BITMAP * block_group->sectorsize;
-        int max_bitmaps = (int)div64_u64(block_group->key.offset +
-                                         bytes_per_bg - 1, bytes_per_bg);
-        BUG_ON(block_group->total_bitmaps >= max_bitmaps);
-
-        info->offset = offset_to_bitmap(block_group, offset);
+        info->offset = offset_to_bitmap(ctl, offset);
         info->bytes = 0;
-        link_free_space(block_group, info);
-        block_group->total_bitmaps++;
+        link_free_space(ctl, info);
+        ctl->total_bitmaps++;
 
-        recalculate_thresholds(block_group);
+        ctl->op->recalc_thresholds(ctl);
 }
 
-static void free_bitmap(struct btrfs_block_group_cache *block_group,
+static void free_bitmap(struct btrfs_free_space_ctl *ctl,
                         struct btrfs_free_space *bitmap_info)
 {
-        unlink_free_space(block_group, bitmap_info);
+        unlink_free_space(ctl, bitmap_info);
         kfree(bitmap_info->bitmap);
         kmem_cache_free(btrfs_free_space_cachep, bitmap_info);
-        block_group->total_bitmaps--;
-        recalculate_thresholds(block_group);
+        ctl->total_bitmaps--;
+        ctl->op->recalc_thresholds(ctl);
 }
 
-static noinline int remove_from_bitmap(struct btrfs_block_group_cache *block_group,
+static noinline int remove_from_bitmap(struct btrfs_free_space_ctl *ctl,
                               struct btrfs_free_space *bitmap_info,
                               u64 *offset, u64 *bytes)
 {
@@ -1268,8 +1263,7 @@ static noinline int remove_from_bitmap(struct btrfs_block_group_cache *block_gro
         int ret;
 
 again:
-        end = bitmap_info->offset +
-                (u64)(BITS_PER_BITMAP * block_group->sectorsize) - 1;
+        end = bitmap_info->offset + (u64)(BITS_PER_BITMAP * ctl->unit) - 1;
 
         /*
          * XXX - this can go away after a few releases.
@@ -1284,24 +1278,22 @@ again:
         search_start = *offset;
         search_bytes = *bytes;
         search_bytes = min(search_bytes, end - search_start + 1);
-        ret = search_bitmap(block_group, bitmap_info, &search_start,
-                            &search_bytes);
+        ret = search_bitmap(ctl, bitmap_info, &search_start, &search_bytes);
         BUG_ON(ret < 0 || search_start != *offset);
 
         if (*offset > bitmap_info->offset && *offset + *bytes > end) {
-                bitmap_clear_bits(block_group, bitmap_info, *offset,
-                                  end - *offset + 1);
+                bitmap_clear_bits(ctl, bitmap_info, *offset, end - *offset + 1);
                 *bytes -= end - *offset + 1;
                 *offset = end + 1;
         } else if (*offset >= bitmap_info->offset && *offset + *bytes <= end) {
-                bitmap_clear_bits(block_group, bitmap_info, *offset, *bytes);
+                bitmap_clear_bits(ctl, bitmap_info, *offset, *bytes);
                 *bytes = 0;
         }
 
         if (*bytes) {
                 struct rb_node *next = rb_next(&bitmap_info->offset_index);
                 if (!bitmap_info->bytes)
-                        free_bitmap(block_group, bitmap_info);
+                        free_bitmap(ctl, bitmap_info);
 
                 /*
                  * no entry after this bitmap, but we still have bytes to
@@ -1328,31 +1320,28 @@ again:
                  */
                 search_start = *offset;
                 search_bytes = *bytes;
-                ret = search_bitmap(block_group, bitmap_info, &search_start,
+                ret = search_bitmap(ctl, bitmap_info, &search_start,
                                     &search_bytes);
                 if (ret < 0 || search_start != *offset)
                         return -EAGAIN;
 
                 goto again;
         } else if (!bitmap_info->bytes)
-                free_bitmap(block_group, bitmap_info);
+                free_bitmap(ctl, bitmap_info);
 
         return 0;
 }
 
-static int insert_into_bitmap(struct btrfs_block_group_cache *block_group,
-                              struct btrfs_free_space *info)
+static bool use_bitmap(struct btrfs_free_space_ctl *ctl,
+                      struct btrfs_free_space *info)
 {
-        struct btrfs_free_space *bitmap_info;
-        int added = 0;
-        u64 bytes, offset, end;
-        int ret;
+        struct btrfs_block_group_cache *block_group = ctl->private;
 
         /*
          * If we are below the extents threshold then we can add this as an
          * extent, and don't have to deal with the bitmap
          */
-        if (block_group->free_extents < block_group->extents_thresh) {
+        if (ctl->free_extents < ctl->extents_thresh) {
                 /*
                  * If this block group has some small extents we don't want to
                  * use up all of our free slots in the cache with them, we want
@@ -1361,11 +1350,10 @@ static int insert_into_bitmap(struct btrfs_block_group_cache *block_group,
                  * the overhead of a bitmap if we don't have to.
                  */
                 if (info->bytes <= block_group->sectorsize * 4) {
-                        if (block_group->free_extents * 2 <=
-                            block_group->extents_thresh)
-                                return 0;
+                        if (ctl->free_extents * 2 <= ctl->extents_thresh)
+                                return false;
                 } else {
-                        return 0;
+                        return false;
                 }
         }
 
@@ -1375,31 +1363,42 @@ static int insert_into_bitmap(struct btrfs_block_group_cache *block_group,
          */
         if (BITS_PER_BITMAP * block_group->sectorsize >
             block_group->key.offset)
-                return 0;
+                return false;
+
+        return true;
+}
+
+static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl,
+                              struct btrfs_free_space *info)
+{
+        struct btrfs_free_space *bitmap_info;
+        int added = 0;
+        u64 bytes, offset, end;
+        int ret;
 
         bytes = info->bytes;
         offset = info->offset;
 
+        if (!ctl->op->use_bitmap(ctl, info))
+                return 0;
+
 again:
-        bitmap_info = tree_search_offset(block_group,
-                                         offset_to_bitmap(block_group, offset),
+        bitmap_info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                                          1, 0);
         if (!bitmap_info) {
                 BUG_ON(added);
                 goto new_bitmap;
         }
 
-        end = bitmap_info->offset +
-                (u64)(BITS_PER_BITMAP * block_group->sectorsize);
+        end = bitmap_info->offset + (u64)(BITS_PER_BITMAP * ctl->unit);
 
         if (offset >= bitmap_info->offset && offset + bytes > end) {
-                bitmap_set_bits(block_group, bitmap_info, offset,
-                                end - offset);
+                bitmap_set_bits(ctl, bitmap_info, offset, end - offset);
                 bytes -= end - offset;
                 offset = end;
                 added = 0;
         } else if (offset >= bitmap_info->offset && offset + bytes <= end) {
-                bitmap_set_bits(block_group, bitmap_info, offset, bytes);
+                bitmap_set_bits(ctl, bitmap_info, offset, bytes);
                 bytes = 0;
         } else {
                 BUG();
@@ -1413,19 +1412,19 @@ again:
 
 new_bitmap:
         if (info && info->bitmap) {
-                add_new_bitmap(block_group, info, offset);
+                add_new_bitmap(ctl, info, offset);
                 added = 1;
                 info = NULL;
                 goto again;
         } else {
-                spin_unlock(&block_group->tree_lock);
+                spin_unlock(&ctl->tree_lock);
 
                 /* no pre-allocated info, allocate a new one */
                 if (!info) {
                         info = kmem_cache_zalloc(btrfs_free_space_cachep,
                                                  GFP_NOFS);
                         if (!info) {
-                                spin_lock(&block_group->tree_lock);
+                                spin_lock(&ctl->tree_lock);
                                 ret = -ENOMEM;
                                 goto out;
                         }
@@ -1433,7 +1432,7 @@ new_bitmap:
 
                 /* allocate the bitmap */
                 info->bitmap = kzalloc(PAGE_CACHE_SIZE, GFP_NOFS);
-                spin_lock(&block_group->tree_lock);
+                spin_lock(&ctl->tree_lock);
                 if (!info->bitmap) {
                         ret = -ENOMEM;
                         goto out;
@@ -1451,7 +1450,7 @@ out:
         return ret;
 }
 
-bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
+bool try_merge_free_space(struct btrfs_free_space_ctl *ctl,
                           struct btrfs_free_space *info, bool update_stat)
 {
         struct btrfs_free_space *left_info;
@@ -1465,18 +1464,18 @@ bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
          * are adding, if there is remove that struct and add a new one to
          * cover the entire range
          */
-        right_info = tree_search_offset(block_group, offset + bytes, 0, 0);
+        right_info = tree_search_offset(ctl, offset + bytes, 0, 0);
         if (right_info && rb_prev(&right_info->offset_index))
                 left_info = rb_entry(rb_prev(&right_info->offset_index),
                                      struct btrfs_free_space, offset_index);
         else
-                left_info = tree_search_offset(block_group, offset - 1, 0, 0);
+                left_info = tree_search_offset(ctl, offset - 1, 0, 0);
 
         if (right_info && !right_info->bitmap) {
                 if (update_stat)
-                        unlink_free_space(block_group, right_info);
+                        unlink_free_space(ctl, right_info);
                 else
-                        __unlink_free_space(block_group, right_info);
+                        __unlink_free_space(ctl, right_info);
                 info->bytes += right_info->bytes;
                 kmem_cache_free(btrfs_free_space_cachep, right_info);
                 merged = true;
@@ -1485,9 +1484,9 @@ bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
         if (left_info && !left_info->bitmap &&
             left_info->offset + left_info->bytes == offset) {
                 if (update_stat)
-                        unlink_free_space(block_group, left_info);
+                        unlink_free_space(ctl, left_info);
                 else
-                        __unlink_free_space(block_group, left_info);
+                        __unlink_free_space(ctl, left_info);
                 info->offset = left_info->offset;
                 info->bytes += left_info->bytes;
                 kmem_cache_free(btrfs_free_space_cachep, left_info);
@@ -1500,6 +1499,7 @@ bool try_merge_free_space(struct btrfs_block_group_cache *block_group,
 int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
                          u64 offset, u64 bytes)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *info;
         int ret = 0;
 
@@ -1510,9 +1510,9 @@ int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
         info->offset = offset;
         info->bytes = bytes;
 
-        spin_lock(&block_group->tree_lock);
+        spin_lock(&ctl->tree_lock);
 
-        if (try_merge_free_space(block_group, info, true))
+        if (try_merge_free_space(ctl, info, true))
                 goto link;
 
         /*
@@ -1520,7 +1520,7 @@ int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
          * extent then we know we're going to have to allocate a new extent, so
          * before we do that see if we need to drop this into a bitmap
          */
-        ret = insert_into_bitmap(block_group, info);
+        ret = insert_into_bitmap(ctl, info);
         if (ret < 0) {
                 goto out;
         } else if (ret) {
@@ -1528,11 +1528,11 @@ int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
                 goto out;
         }
 link:
-        ret = link_free_space(block_group, info);
+        ret = link_free_space(ctl, info);
         if (ret)
                 kmem_cache_free(btrfs_free_space_cachep, info);
 out:
-        spin_unlock(&block_group->tree_lock);
+        spin_unlock(&ctl->tree_lock);
 
         if (ret) {
                 printk(KERN_CRIT "btrfs: unable to add free space :%d\n", ret);
@@ -1545,21 +1545,21 @@ out:
 int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,
                             u64 offset, u64 bytes)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *info;
         struct btrfs_free_space *next_info = NULL;
         int ret = 0;
 
-        spin_lock(&block_group->tree_lock);
+        spin_lock(&ctl->tree_lock);
 
 again:
-        info = tree_search_offset(block_group, offset, 0, 0);
+        info = tree_search_offset(ctl, offset, 0, 0);
         if (!info) {
                 /*
                  * oops didn't find an extent that matched the space we wanted
                  * to remove, look for a bitmap instead
                  */
-                info = tree_search_offset(block_group,
-                                          offset_to_bitmap(block_group, offset),
+                info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                                           1, 0);
                 if (!info) {
                         WARN_ON(1);
@@ -1574,8 +1574,8 @@ again:
                                              offset_index);
 
                 if (next_info->bitmap)
-                        end = next_info->offset + BITS_PER_BITMAP *
-                                block_group->sectorsize - 1;
+                        end = next_info->offset +
+                              BITS_PER_BITMAP * ctl->unit - 1;
                 else
                         end = next_info->offset + next_info->bytes;
 
@@ -1595,20 +1595,20 @@ again:
         }
 
         if (info->bytes == bytes) {
-                unlink_free_space(block_group, info);
+                unlink_free_space(ctl, info);
                 if (info->bitmap) {
                         kfree(info->bitmap);
-                        block_group->total_bitmaps--;
+                        ctl->total_bitmaps--;
                 }
                 kmem_cache_free(btrfs_free_space_cachep, info);
                 goto out_lock;
         }
 
         if (!info->bitmap && info->offset == offset) {
-                unlink_free_space(block_group, info);
+                unlink_free_space(ctl, info);
                 info->offset += bytes;
                 info->bytes -= bytes;
-                link_free_space(block_group, info);
+                link_free_space(ctl, info);
                 goto out_lock;
         }
 
@@ -1622,13 +1622,13 @@ again:
                  * first unlink the old info and then
                  * insert it again after the hole we're creating
                  */
-                unlink_free_space(block_group, info);
+                unlink_free_space(ctl, info);
                 if (offset + bytes < info->offset + info->bytes) {
                         u64 old_end = info->offset + info->bytes;
 
                         info->offset = offset + bytes;
                         info->bytes = old_end - info->offset;
-                        ret = link_free_space(block_group, info);
+                        ret = link_free_space(ctl, info);
                         WARN_ON(ret);
                         if (ret)
                                 goto out_lock;
@@ -1638,7 +1638,7 @@ again:
                          */
                         kmem_cache_free(btrfs_free_space_cachep, info);
                 }
-                spin_unlock(&block_group->tree_lock);
+                spin_unlock(&ctl->tree_lock);
 
                 /* step two, insert a new info struct to cover
                  * anything before the hole
@@ -1649,12 +1649,12 @@ again:
                 goto out;
         }
 
-        ret = remove_from_bitmap(block_group, info, &offset, &bytes);
+        ret = remove_from_bitmap(ctl, info, &offset, &bytes);
         if (ret == -EAGAIN)
                 goto again;
         BUG_ON(ret);
 out_lock:
-        spin_unlock(&block_group->tree_lock);
+        spin_unlock(&ctl->tree_lock);
 out:
         return ret;
 }
@@ -1662,11 +1662,12 @@ out:
 void btrfs_dump_free_space(struct btrfs_block_group_cache *block_group,
                            u64 bytes)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *info;
         struct rb_node *n;
         int count = 0;
 
-        for (n = rb_first(&block_group->free_space_offset); n; n = rb_next(n)) {
+        for (n = rb_first(&ctl->free_space_offset); n; n = rb_next(n)) {
                 info = rb_entry(n, struct btrfs_free_space, offset_index);
                 if (info->bytes >= bytes)
                         count++;
@@ -1681,6 +1682,30 @@ void btrfs_dump_free_space(struct btrfs_block_group_cache *block_group,
                "\n", count);
 }
 
+static struct btrfs_free_space_op free_space_op = {
+        .recalc_thresholds      = recalculate_thresholds,
+        .use_bitmap             = use_bitmap,
+};
+
+void btrfs_init_free_space_ctl(struct btrfs_block_group_cache *block_group)
+{
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
+
+        spin_lock_init(&ctl->tree_lock);
+        ctl->unit = block_group->sectorsize;
+        ctl->start = block_group->key.objectid;
+        ctl->private = block_group;
+        ctl->op = &free_space_op;
+
+        /*
+         * 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
+         */
+        ctl->extents_thresh = ((1024 * 32) / 2) /
+                                sizeof(struct btrfs_free_space);
+}
+
 /*
  * for a given cluster, put all of its extents back into the free
  * space cache.  If the block group passed doesn't match the block group
@@ -1692,6 +1717,7 @@ __btrfs_return_cluster_to_free_space(
                              struct btrfs_block_group_cache *block_group,
                              struct btrfs_free_cluster *cluster)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *entry;
         struct rb_node *node;
 
@@ -1713,8 +1739,8 @@ __btrfs_return_cluster_to_free_space(
 
                 bitmap = (entry->bitmap != NULL);
                 if (!bitmap)
-                        try_merge_free_space(block_group, entry, false);
-                tree_insert_offset(&block_group->free_space_offset,
+                        try_merge_free_space(ctl, entry, false);
+                tree_insert_offset(&ctl->free_space_offset,
                                    entry->offset, &entry->offset_index, bitmap);
         }
         cluster->root = RB_ROOT;
@@ -1727,12 +1753,13 @@ out:
 
 void btrfs_remove_free_space_cache(struct btrfs_block_group_cache *block_group)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *info;
         struct rb_node *node;
         struct btrfs_free_cluster *cluster;
         struct list_head *head;
 
-        spin_lock(&block_group->tree_lock);
+        spin_lock(&ctl->tree_lock);
         while ((head = block_group->cluster_list.next) !=
                &block_group->cluster_list) {
                 cluster = list_entry(head, struct btrfs_free_cluster,
@@ -1741,57 +1768,58 @@ void btrfs_remove_free_space_cache(struct btrfs_block_group_cache *block_group)
                 WARN_ON(cluster->block_group != block_group);
                 __btrfs_return_cluster_to_free_space(block_group, cluster);
                 if (need_resched()) {
-                        spin_unlock(&block_group->tree_lock);
+                        spin_unlock(&ctl->tree_lock);
                         cond_resched();
-                        spin_lock(&block_group->tree_lock);
+                        spin_lock(&ctl->tree_lock);
                 }
         }
 
-        while ((node = rb_last(&block_group->free_space_offset)) != NULL) {
+        while ((node = rb_last(&ctl->free_space_offset)) != NULL) {
                 info = rb_entry(node, struct btrfs_free_space, offset_index);
-                unlink_free_space(block_group, info);
+                unlink_free_space(ctl, info);
                 if (info->bitmap)
                         kfree(info->bitmap);
                 kmem_cache_free(btrfs_free_space_cachep, info);
                 if (need_resched()) {
-                        spin_unlock(&block_group->tree_lock);
+                        spin_unlock(&ctl->tree_lock);
                         cond_resched();
-                        spin_lock(&block_group->tree_lock);
+                        spin_lock(&ctl->tree_lock);
                 }
         }
 
-        spin_unlock(&block_group->tree_lock);
+        spin_unlock(&ctl->tree_lock);
 }
 
 u64 btrfs_find_space_for_alloc(struct btrfs_block_group_cache *block_group,
                                u64 offset, u64 bytes, u64 empty_size)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *entry = NULL;
         u64 bytes_search = bytes + empty_size;
         u64 ret = 0;
 
-        spin_lock(&block_group->tree_lock);
-        entry = find_free_space(block_group, &offset, &bytes_search, 0);
+        spin_lock(&ctl->tree_lock);
+        entry = find_free_space(ctl, &offset, &bytes_search);
         if (!entry)
                 goto out;
 
         ret = offset;
         if (entry->bitmap) {
-                bitmap_clear_bits(block_group, entry, offset, bytes);
+                bitmap_clear_bits(ctl, entry, offset, bytes);
                 if (!entry->bytes)
-                        free_bitmap(block_group, entry);
+                        free_bitmap(ctl, entry);
         } else {
-                unlink_free_space(block_group, entry);
+                unlink_free_space(ctl, entry);
                 entry->offset += bytes;
                 entry->bytes -= bytes;
                 if (!entry->bytes)
                         kmem_cache_free(btrfs_free_space_cachep, entry);
                 else
-                        link_free_space(block_group, entry);
+                        link_free_space(ctl, entry);
         }
 
 out:
-        spin_unlock(&block_group->tree_lock);
+        spin_unlock(&ctl->tree_lock);
 
         return ret;
 }
@@ -1808,6 +1836,7 @@ int btrfs_return_cluster_to_free_space(
                                struct btrfs_block_group_cache *block_group,
                                struct btrfs_free_cluster *cluster)
 {
+        struct btrfs_free_space_ctl *ctl;
         int ret;
 
         /* first, get a safe pointer to the block group */
@@ -1826,10 +1855,12 @@ int btrfs_return_cluster_to_free_space(
         atomic_inc(&block_group->count);
         spin_unlock(&cluster->lock);
 
+        ctl = block_group->free_space_ctl;
+
         /* now return any extents the cluster had on it */
-        spin_lock(&block_group->tree_lock);
+        spin_lock(&ctl->tree_lock);
         ret = __btrfs_return_cluster_to_free_space(block_group, cluster);
-        spin_unlock(&block_group->tree_lock);
+        spin_unlock(&ctl->tree_lock);
 
         /* finally drop our ref */
         btrfs_put_block_group(block_group);
@@ -1841,6 +1872,7 @@ static u64 btrfs_alloc_from_bitmap(struct btrfs_block_group_cache *block_group,
                                    struct btrfs_free_space *entry,
                                    u64 bytes, u64 min_start)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         int err;
         u64 search_start = cluster->window_start;
         u64 search_bytes = bytes;
@@ -1849,13 +1881,12 @@ static u64 btrfs_alloc_from_bitmap(struct btrfs_block_group_cache *block_group,
         search_start = min_start;
         search_bytes = bytes;
 
-        err = search_bitmap(block_group, entry, &search_start,
-                            &search_bytes);
+        err = search_bitmap(ctl, entry, &search_start, &search_bytes);
         if (err)
                 return 0;
 
         ret = search_start;
-        bitmap_clear_bits(block_group, entry, ret, bytes);
+        bitmap_clear_bits(ctl, entry, ret, bytes);
 
         return ret;
 }
@@ -1869,6 +1900,7 @@ u64 btrfs_alloc_from_cluster(struct btrfs_block_group_cache *block_group,
                              struct btrfs_free_cluster *cluster, u64 bytes,
                              u64 min_start)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *entry = NULL;
         struct rb_node *node;
         u64 ret = 0;
@@ -1929,20 +1961,20 @@ out:
         if (!ret)
                 return 0;
 
-        spin_lock(&block_group->tree_lock);
+        spin_lock(&ctl->tree_lock);
 
-        block_group->free_space -= bytes;
+        ctl->free_space -= bytes;
         if (entry->bytes == 0) {
-                block_group->free_extents--;
+                ctl->free_extents--;
                 if (entry->bitmap) {
                         kfree(entry->bitmap);
-                        block_group->total_bitmaps--;
-                        recalculate_thresholds(block_group);
+                        ctl->total_bitmaps--;
+                        ctl->op->recalc_thresholds(ctl);
                 }
                 kmem_cache_free(btrfs_free_space_cachep, entry);
         }
 
-        spin_unlock(&block_group->tree_lock);
+        spin_unlock(&ctl->tree_lock);
 
         return ret;
 }
@@ -1952,6 +1984,7 @@ static int btrfs_bitmap_cluster(struct btrfs_block_group_cache *block_group,
                                 struct btrfs_free_cluster *cluster,
                                 u64 offset, u64 bytes, u64 min_bytes)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         unsigned long next_zero;
         unsigned long i;
         unsigned long search_bits;
@@ -2006,7 +2039,7 @@ again:
 
         cluster->window_start = start * block_group->sectorsize +
                 entry->offset;
-        rb_erase(&entry->offset_index, &block_group->free_space_offset);
+        rb_erase(&entry->offset_index, &ctl->free_space_offset);
         ret = tree_insert_offset(&cluster->root, entry->offset,
                                  &entry->offset_index, 1);
         BUG_ON(ret);
@@ -2021,6 +2054,7 @@ static int setup_cluster_no_bitmap(struct btrfs_block_group_cache *block_group,
                                    struct btrfs_free_cluster *cluster,
                                    u64 offset, u64 bytes, u64 min_bytes)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *first = NULL;
         struct btrfs_free_space *entry = NULL;
         struct btrfs_free_space *prev = NULL;
@@ -2031,7 +2065,7 @@ static int setup_cluster_no_bitmap(struct btrfs_block_group_cache *block_group,
         u64 max_extent;
         u64 max_gap = 128 * 1024;
 
-        entry = tree_search_offset(block_group, offset, 0, 1);
+        entry = tree_search_offset(ctl, offset, 0, 1);
         if (!entry)
                 return -ENOSPC;
 
@@ -2097,7 +2131,7 @@ static int setup_cluster_no_bitmap(struct btrfs_block_group_cache *block_group,
                 if (entry->bitmap)
                         continue;
 
-                rb_erase(&entry->offset_index, &block_group->free_space_offset);
+                rb_erase(&entry->offset_index, &ctl->free_space_offset);
                 ret = tree_insert_offset(&cluster->root, entry->offset,
                                          &entry->offset_index, 0);
                 BUG_ON(ret);
@@ -2116,16 +2150,15 @@ static int setup_cluster_bitmap(struct btrfs_block_group_cache *block_group,
                                 struct btrfs_free_cluster *cluster,
                                 u64 offset, u64 bytes, u64 min_bytes)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *entry;
         struct rb_node *node;
         int ret = -ENOSPC;
 
-        if (block_group->total_bitmaps == 0)
+        if (ctl->total_bitmaps == 0)
                 return -ENOSPC;
 
-        entry = tree_search_offset(block_group,
-                                   offset_to_bitmap(block_group, offset),
-                                   0, 1);
+        entry = tree_search_offset(ctl, offset_to_bitmap(ctl, offset), 0, 1);
         if (!entry)
                 return -ENOSPC;
 
@@ -2158,6 +2191,7 @@ int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
                              struct btrfs_free_cluster *cluster,
                              u64 offset, u64 bytes, u64 empty_size)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         u64 min_bytes;
         int ret;
 
@@ -2177,14 +2211,14 @@ int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
         } else
                 min_bytes = max(bytes, (bytes + empty_size) >> 2);
 
-        spin_lock(&block_group->tree_lock);
+        spin_lock(&ctl->tree_lock);
 
         /*
          * If we know we don't have enough space to make a cluster don't even
          * bother doing all the work to try and find one.
          */
-        if (block_group->free_space < min_bytes) {
-                spin_unlock(&block_group->tree_lock);
+        if (ctl->free_space < min_bytes) {
+                spin_unlock(&ctl->tree_lock);
                 return -ENOSPC;
         }
 
@@ -2210,7 +2244,7 @@ int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
         }
 out:
         spin_unlock(&cluster->lock);
-        spin_unlock(&block_group->tree_lock);
+        spin_unlock(&ctl->tree_lock);
 
         return ret;
 }
@@ -2231,6 +2265,7 @@ void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster)
 int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
                            u64 *trimmed, u64 start, u64 end, u64 minlen)
 {
+        struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
         struct btrfs_free_space *entry = NULL;
         struct btrfs_fs_info *fs_info = block_group->fs_info;
         u64 bytes = 0;
@@ -2240,52 +2275,50 @@ int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
         *trimmed = 0;
 
         while (start < end) {
-                spin_lock(&block_group->tree_lock);
+                spin_lock(&ctl->tree_lock);
 
-                if (block_group->free_space < minlen) {
-                        spin_unlock(&block_group->tree_lock);
+                if (ctl->free_space < minlen) {
+                        spin_unlock(&ctl->tree_lock);
                         break;
                 }
 
-                entry = tree_search_offset(block_group, start, 0, 1);
+                entry = tree_search_offset(ctl, start, 0, 1);
                 if (!entry)
-                        entry = tree_search_offset(block_group,
-                                                   offset_to_bitmap(block_group,
-                                                                    start),
+                        entry = tree_search_offset(ctl,
+                                                   offset_to_bitmap(ctl, start),
                                                    1, 1);
 
                 if (!entry || entry->offset >= end) {
-                        spin_unlock(&block_group->tree_lock);
+                        spin_unlock(&ctl->tree_lock);
                         break;
                 }
 
                 if (entry->bitmap) {
-                        ret = search_bitmap(block_group, entry, &start, &bytes);
+                        ret = search_bitmap(ctl, entry, &start, &bytes);
                         if (!ret) {
                                 if (start >= end) {
-                                        spin_unlock(&block_group->tree_lock);
+                                        spin_unlock(&ctl->tree_lock);
                                         break;
                                 }
                                 bytes = min(bytes, end - start);
-                                bitmap_clear_bits(block_group, entry,
-                                                  start, bytes);
+                                bitmap_clear_bits(ctl, entry, start, bytes);
                                 if (entry->bytes == 0)
-                                        free_bitmap(block_group, entry);
+                                        free_bitmap(ctl, entry);
                         } else {
                                 start = entry->offset + BITS_PER_BITMAP *
                                         block_group->sectorsize;
-                                spin_unlock(&block_group->tree_lock);
+                                spin_unlock(&ctl->tree_lock);
                                 ret = 0;
                                 continue;
                         }
                 } else {
                         start = entry->offset;
                         bytes = min(entry->bytes, end - start);
-                        unlink_free_space(block_group, entry);
+                        unlink_free_space(ctl, entry);
                         kfree(entry);
                 }
 
-                spin_unlock(&block_group->tree_lock);
+                spin_unlock(&ctl->tree_lock);
 
                 if (bytes >= minlen) {
                         int update_ret;
@@ -2297,8 +2330,7 @@ int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
                                                          bytes,
                                                          &actually_trimmed);
 
-                        btrfs_add_free_space(block_group,
-                                             start, bytes);
+                        btrfs_add_free_space(block_group, start, bytes);
                         if (!update_ret)
                                 btrfs_update_reserved_bytes(block_group,
                                                             bytes, 0, 1);
diff --git a/fs/btrfs/free-space-cache.h b/fs/btrfs/free-space-cache.h
index 12b2b5165f8a..a64a23fae1eb 100644
--- a/fs/btrfs/free-space-cache.h
+++ b/fs/btrfs/free-space-cache.h
@@ -27,6 +27,25 @@ struct btrfs_free_space {
         struct list_head list;
 };
 
+struct btrfs_free_space_ctl {
+        spinlock_t tree_lock;
+        struct rb_root free_space_offset;
+        u64 free_space;
+        int extents_thresh;
+        int free_extents;
+        int total_bitmaps;
+        int unit;
+        u64 start;
+        struct btrfs_free_space_op *op;
+        void *private;
+};
+
+struct btrfs_free_space_op {
+        void (*recalc_thresholds)(struct btrfs_free_space_ctl *ctl);
+        bool (*use_bitmap)(struct btrfs_free_space_ctl *ctl,
+                           struct btrfs_free_space *info);
+};
+
 struct inode *lookup_free_space_inode(struct btrfs_root *root,
                                       struct btrfs_block_group_cache
                                       *block_group, struct btrfs_path *path);
@@ -45,6 +64,7 @@ int btrfs_write_out_cache(struct btrfs_root *root,
                           struct btrfs_trans_handle *trans,
                           struct btrfs_block_group_cache *block_group,
                           struct btrfs_path *path);
+void btrfs_init_free_space_ctl(struct btrfs_block_group_cache *block_group);
 int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
                          u64 bytenr, u64 size);
 int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,