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[BUG] Since the support of block size (sector size) < page size for btrfs, test case generic/563 fails with 4K block size and 64K page size: --- tests/generic/563.out 2024-04-25 18:13:45.178550333 +0930 +++ /home/adam/xfstests-dev/results//generic/563.out.bad 2024-09-30 09:09:16.155312379 +0930 @@ -3,7 +3,8 @@ read is in range write is in range write -> read/write -read is in range +read has value of 8388608 +read is NOT in range -33792 .. 33792 write is in range ... [CAUSE] The test case creates a 8MiB file, then does buffered write into the 8MiB using 4K block size, to overwrite the whole file. On 4K page sized systems, since the write range covers the full block and page, btrfs will not bother reading the page, just like what XFS and EXT4 do. But on 64K page sized systems, although the 4K sized write is still block aligned, it's not page aligned anymore, thus btrfs will read the full page, which will be accounted by cgroup and fail the test. As the test case itself expects such 4K block aligned write should not trigger any read. Such expected behavior is an optimization to reduce folio reads when possible, and unfortunately btrfs does not implement such optimization. [FIX] To skip the full page read, we need to do the following modification: - Do not trigger full page read as long as the buffered write is block aligned This is pretty simple by modifying the check inside prepare_uptodate_page(). - Skip already uptodate blocks during full page read Or we can lead to the following data corruption: 0 32K 64K |///////| | Where the file range [0, 32K) is dirtied by buffered write, the remaining range [32K, 64K) is not. When reading the full page, since [0,32K) is only dirtied but not written back, there is no data extent map for it, but a hole covering [0, 64k). If we continue reading the full page range [0, 64K), the dirtied range will be filled with 0 (since there is only a hole covering the whole range). This causes the dirtied range to get lost. With this optimization, btrfs can pass generic/563 even if the page size is larger than fs block size. Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.