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btrfs-progs: Fix false ENOSPC alert by tracking used space correctly
[BUG] There is a bug report of unexpected ENOSPC from btrfs-convert. kdave#123 After some debug, 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 relie 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 trace 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: kdave#123 Signed-off-by: Qu Wenruo <email@example.com>
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