1 files changed, 9 insertions, 36 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 9ef8f99d5a2a..7c644f810816 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5615,48 +5615,21 @@ void btrfs_block_rsv_release(struct btrfs_root *root,
                                 num_bytes);
 }
 
-/*
- * helper to calculate size of global block reservation.
- * the desired value is sum of space used by extent tree,
- * checksum tree and root tree
- */
-static u64 calc_global_metadata_size(struct btrfs_fs_info *fs_info)
-{
-        struct btrfs_space_info *sinfo;
-        u64 num_bytes;
-        u64 meta_used;
-        u64 data_used;
-        int csum_size = btrfs_super_csum_size(fs_info->super_copy);
-
-        sinfo = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_DATA);
-        spin_lock(&sinfo->lock);
-        data_used = sinfo->bytes_used;
-        spin_unlock(&sinfo->lock);
-
-        sinfo = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);
-        spin_lock(&sinfo->lock);
-        if (sinfo->flags & BTRFS_BLOCK_GROUP_DATA)
-                data_used = 0;
-        meta_used = sinfo->bytes_used;
-        spin_unlock(&sinfo->lock);
-
-        num_bytes = (data_used >> fs_info->sb->s_blocksize_bits) *
-                    csum_size * 2;
-        num_bytes += div_u64(data_used + meta_used, 50);
-
-        if (num_bytes * 3 > meta_used)
-                num_bytes = div_u64(meta_used, 3);
-
-        return ALIGN(num_bytes, fs_info->extent_root->nodesize << 10);
-}
-
 static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
 {
         struct btrfs_block_rsv *block_rsv = &fs_info->global_block_rsv;
         struct btrfs_space_info *sinfo = block_rsv->space_info;
         u64 num_bytes;
 
-        num_bytes = calc_global_metadata_size(fs_info);
+        /*
+         * The global block rsv is based on the size of the extent tree, the
+         * checksum tree and the root tree.  If the fs is empty we want to set
+         * it to a minimal amount for safety.
+         */
+        num_bytes = btrfs_root_used(&fs_info->extent_root->root_item) +
+                btrfs_root_used(&fs_info->csum_root->root_item) +
+                btrfs_root_used(&fs_info->tree_root->root_item);
+        num_bytes = max_t(u64, num_bytes, SZ_16M);
 
         spin_lock(&sinfo->lock);
         spin_lock(&block_rsv->lock);