[BUG]
There is a bug report of unexpected ENOSPC from btrfs-convert, issue #123.
After some debugging, even when we have enough unallocated space, we
still hit ENOSPC at btrfs_reserve_extent().
[CAUSE]
Btrfs-progs relies on chunk preallocator to make enough space for
data/metadata.
However after the introduction of delayed-ref, it's no longer reliable
to rely on btrfs_space_info::bytes_used and
btrfs_space_info::bytes_pinned to calculate used metadata space.
For a running transaction with a lot of allocated tree blocks,
btrfs_space_info::bytes_used stays its original value, and will only be
updated when running delayed ref.
This makes btrfs-progs chunk preallocator completely useless. And for
btrfs-convert/mkfs.btrfs --rootdir, if we're going to have enough
metadata to fill a metadata block group in one transaction, we will hit
ENOSPC no matter whether we have enough unallocated space.
[FIX]
This patch will introduce btrfs_space_info::bytes_reserved to track how
many space we have reserved but not yet committed to extent tree.
To support this change, this commit also introduces the following
modification:
- More comment on btrfs_space_info::bytes_*
To make code a little easier to read
- Export update_space_info() to preallocate empty data/metadata space
info for mkfs.
For mkfs, we only have a temporary fs image with SYSTEM chunk only.
Export update_space_info() so that we can preallocate empty
data/metadata space info before we start a transaction.
- Proper btrfs_space_info::bytes_reserved update
The timing is the as kernel (except we don't need to update
bytes_reserved for data extents)
* Increase bytes_reserved when call alloc_reserved_tree_block()
* Decrease bytes_reserved when running delayed refs
With the help of head->must_insert_reserved to determine whether we
need to decrease.
Issue: #123
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
c31edf610c