btrfs: allow to run delayed refs by bytes to be released instead of count

When running delayed references, through btrfs_run_delayed_refs(), we can
specify how many to run, run all existing delayed references and keep
running delayed references while we can find any. This is controlled with
the value of the 'count' argument, where a value of 0 means to run all
delayed references that exist by the time btrfs_run_delayed_refs() is
called, (unsigned long)-1 means to keep running delayed references while
we are able find any, and any other value to run that exact number of
delayed references.

Typically a specific value other than 0 or -1 is used when flushing space
to try to release a certain amount of bytes for a ticket. In this case
we just simply calculate how many delayed reference heads correspond to a
specific amount of bytes, with calc_delayed_refs_nr(). However that only
takes into account the space reserved for the reference heads themselves,
and does not account for the space reserved for deleting checksums from
the csum tree (see add_delayed_ref_head() and update_existing_head_ref())
in case we are going to delete a data extent. This means we may end up
running more delayed references than necessary in case we process delayed
references for deleting a data extent.

So change the logic of btrfs_run_delayed_refs() to take a bytes argument
to specify how many bytes of delayed references to run/release, using the
special values of 0 to mean all existing delayed references and U64_MAX
(or (u64)-1) to keep running delayed references while we can find any.

This prevents running more delayed references than necessary, when we have
delayed references for deleting data extents, but also makes the upcoming
changes/patches simpler and it's preparatory work for them.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/btrfs/extent-tree.h b/fs/btrfs/extent-tree.h
index dd31ee85f360..397cccafc885 100644
--- a/fs/btrfs/extent-tree.h
+++ b/fs/btrfs/extent-tree.h
@@ -92,8 +92,8 @@ int btrfs_get_extent_inline_ref_type(const struct extent_buffer *eb,
 				     enum btrfs_inline_ref_type is_data);
 u64 hash_extent_data_ref(u64 root_objectid, u64 owner, u64 offset);
 
-int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans, unsigned long count);
-void btrfs_cleanup_ref_head_accounting(struct btrfs_fs_info *fs_info,
+int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans, u64 min_bytes);
+u64 btrfs_cleanup_ref_head_accounting(struct btrfs_fs_info *fs_info,
 				  struct btrfs_delayed_ref_root *delayed_refs,
 				  struct btrfs_delayed_ref_head *head);
 int btrfs_lookup_data_extent(struct btrfs_fs_info *fs_info, u64 start, u64 len);