From: Qu Wenruo <wqu@suse.com>
To: linux-btrfs@vger.kernel.org
Subject: [PATCH v3 0/3] btrfs: more explaination on extent_map members
Date: Fri, 5 Apr 2024 13:57:10 +1030 [thread overview]
Message-ID: <cover.1712287421.git.wqu@suse.com> (raw)
[REPO]
https://github.com/adam900710/linux.git/ em_cleanup
[CHANGELOG]
v3:
- Rebased to latest for-next branch
- Further comments polishment
- Coding style update to follow the guideline
v2:
- Add Filipe's cleanup on mod_start/mod_len
These two members are no longer utilized, saving me quite some time on
digging into their usage.
- Update the comments of the extent_map structure
To make them more readable and less confusing.
- Further cleanup for inline extent_map reading
- A new patch to do extra sanity checks for create_io_em()
Firstly pure NOCOW writes should not call create_io_em(), secondly
with the new knowledge of extent_map, it's easier to do extra sanity
checks for the already pretty long parameter list.
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.
- 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 (3):
btrfs: add extra comments on extent_map members
btrfs: simplify the inline extent map creation
btrfs: add extra sanity checks for create_io_em()
fs/btrfs/extent_map.h | 52 ++++++++++++++++++++++++++++++++++++++++++-
fs/btrfs/file-item.c | 20 ++++++++---------
fs/btrfs/inode.c | 40 ++++++++++++++++++++++++++++++++-
3 files changed, 100 insertions(+), 12 deletions(-)
--
2.44.0
next reply other threads:[~2024-04-05 3:27 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-05 3:27 Qu Wenruo [this message]
2024-04-05 3:27 ` [PATCH v3 1/3] btrfs: add extra comments on extent_map members Qu Wenruo
2024-04-05 12:24 ` Filipe Manana
2024-04-05 21:36 ` Qu Wenruo
2024-04-08 11:11 ` Filipe Manana
2024-04-08 22:05 ` Qu Wenruo
2024-04-05 3:27 ` [PATCH v3 2/3] btrfs: simplify the inline extent map creation Qu Wenruo
2024-04-05 12:25 ` Filipe Manana
2024-04-05 3:27 ` [PATCH v3 3/3] btrfs: add extra sanity checks for create_io_em() Qu Wenruo
2024-04-05 12:27 ` Filipe Manana
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