Btrfs: don't use global block reservation for inode cache truncation

It is very likely that there are lots of subvolumes/snapshots in the filesystem,
so if we use global block reservation to do inode cache truncation, we may hog
all the free space that is reserved in global rsv. So it is better that we do
the free space reservation for inode cache truncation by ourselves.

Cc: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/btrfs/inode-map.c b/fs/btrfs/inode-map.c
index 9818d4a3f829..2c66ddbbe670 100644
--- a/fs/btrfs/inode-map.c
+++ b/fs/btrfs/inode-map.c
@@ -429,11 +429,12 @@ int btrfs_save_ino_cache(struct btrfs_root *root,
         num_bytes = trans->bytes_reserved;
         /*
          * 1 item for inode item insertion if need
-         * 3 items for inode item update (in the worst case)
+         * 4 items for inode item update (in the worst case)
+         * 1 items for slack space if we need do truncation
          * 1 item for free space object
          * 3 items for pre-allocation
          */
-        trans->bytes_reserved = btrfs_calc_trans_metadata_size(root, 8);
+        trans->bytes_reserved = btrfs_calc_trans_metadata_size(root, 10);
         ret = btrfs_block_rsv_add(root, trans->block_rsv,
                                   trans->bytes_reserved,
                                   BTRFS_RESERVE_NO_FLUSH);