From: Qu Wenruo <wqu@suse.com>
To: linux-btrfs@vger.kernel.org
Subject: [PATCH 0/2] btrfs: more explaination on extent_map members
Date: Tue, 2 Apr 2024 16:53:18 +1030 [thread overview]
Message-ID: <cover.1712038308.git.wqu@suse.com> (raw)
Btrfs uses extent_map to represent a in-memory file extent.
There are severam members that are 1:1 mappe in on-disk file extent
items and extent maps:
- extent_map::start == key.offset
- extent_map::len == file_extent_num_bytes
- extent_map::ram_bytes == file_extent_ram_bytes
But that's all, the remaining are pretty different:
- Use block_start to indicate holes/inline extents
Meanwhile btrfs on-disk file extent items go with a dedicated type for
inline extents, and disk_bytenr 0 for holes.
- Extra members for fsync optimization
I'm still not 100% sure how mod_start and mod_len really works though.
- Weird block_start/orig_block_len/orig_start
In theory we can directly go with the same file_extent_disk_bytenr,
file_extent_disk_num_bytes and file_extent_offset to calculate the
remaining members (block_start/orig_start/orig_block_len/block_len).
But for whatever reason, we didn't go that path and have a hell of
weird and inconsistent calculation for them.
I do not have the confidence to handle the mess yet, but as the first
step, I would add comments for those members mostly according to
btrfs_extent_item_to_extent_map(), and hopefully we can improve the
situation in not-far-away future.
Qu Wenruo (2):
btrfs: add extra comments on extent_map members
btrfs: simplify the inline extent map creation
fs/btrfs/extent_map.h | 62 ++++++++++++++++++++++++++++++++++++++++++-
fs/btrfs/file-item.c | 14 ++++++----
2 files changed, 70 insertions(+), 6 deletions(-)
--
2.44.0
next reply other threads:[~2024-04-02 6:23 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-02 6:23 Qu Wenruo [this message]
2024-04-02 6:23 ` [PATCH 1/2] btrfs: add extra comments on extent_map members Qu Wenruo
2024-04-02 7:33 ` Andrea Gelmini
2024-04-02 8:25 ` Qu Wenruo
2024-04-02 15:45 ` Filipe Manana
2024-04-02 6:23 ` [PATCH 2/2] btrfs: simplify the inline extent map creation Qu Wenruo
2024-04-02 15:50 ` Filipe Manana
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