[PATCH 2/2] btrfs: only reserve metadata_size for inodes

[Josef Bacik <josef@toxicpanda.com>]

Historically we reserved worst case for every btree operation, and
generally speaking we want to do that in cases where it could be the
worst case.  However for updating inodes we know the inode items are
already in the tree, so it will only be an update operation and never an
insert operation.  This allows us to always reserve only the
metadata_size amount for inode updates rather than the
insert_metadata_size amount.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/delalloc-space.c | 21 +++++++++++++++++----
 fs/btrfs/delayed-inode.c  |  2 +-
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/delalloc-space.c b/fs/btrfs/delalloc-space.c
index 2412be4a3de2..d949d7d2abed 100644
--- a/fs/btrfs/delalloc-space.c
+++ b/fs/btrfs/delalloc-space.c
@@ -251,9 +251,16 @@ static void btrfs_calculate_inode_block_rsv_size(struct btrfs_fs_info *fs_info,
 
 	lockdep_assert_held(&inode->lock);
 	outstanding_extents = inode->outstanding_extents;
-	if (outstanding_extents)
+
+	/*
+	 * Insert size for the number of outstanding extents, 1 normal size for
+	 * updating the inode.
+	 */
+	if (outstanding_extents) {
 		reserve_size = btrfs_calc_insert_metadata_size(fs_info,
-						outstanding_extents + 1);
+						outstanding_extents);
+		reserve_size += btrfs_calc_metadata_size(fs_info, 1);
+	}
 	csum_leaves = btrfs_csum_bytes_to_leaves(fs_info,
 						 inode->csum_bytes);
 	reserve_size += btrfs_calc_insert_metadata_size(fs_info,
@@ -278,10 +285,16 @@ static void calc_inode_reservations(struct btrfs_fs_info *fs_info,
 {
 	u64 nr_extents = count_max_extents(num_bytes);
 	u64 csum_leaves = btrfs_csum_bytes_to_leaves(fs_info, num_bytes);
+	u64 inode_update = btrfs_calc_metadata_size(fs_info, 1);
 
-	/* We add one for the inode update at finish ordered time */
 	*meta_reserve = btrfs_calc_insert_metadata_size(fs_info,
-						nr_extents + csum_leaves + 1);
+						nr_extents + csum_leaves);
+
+	/*
+	 * finish_ordered_io has to update the inode, so add the space required
+	 * for an inode update.
+	 */
+	*meta_reserve += inode_update;
 	*qgroup_reserve = nr_extents * fs_info->nodesize;
 }
 
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index de87ea7ce84d..9318cf761a07 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -612,7 +612,7 @@ static int btrfs_delayed_inode_reserve_metadata(
 	src_rsv = trans->block_rsv;
 	dst_rsv = &fs_info->delayed_block_rsv;
 
-	num_bytes = btrfs_calc_insert_metadata_size(fs_info, 1);
+	num_bytes = btrfs_calc_metadata_size(fs_info, 1);
 
 	/*
 	 * btrfs_dirty_inode will update the inode under btrfs_join_transaction
-- 
2.21.0