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Currently reading an inline data extent will zero out the remaining range in the page. This is not yet causing problems even for block size < page size (subpage) cases because: 1) An inline data extent always starts at file offset 0 Meaning at page read, we always read the inline extent first, before any other blocks in the page. Then later blocks are properly read out and re-fill the zeroed out ranges. 2) Currently btrfs will read out the whole page if a buffered write is not page aligned So a page is either fully uptodate at buffered write time (covers the whole page), or we will read out the whole page first. Meaning there is nothing to lose for such an inline extent read. But it's still not ideal: - We're zeroing out the page twice Once done by read_inline_extent()/uncompress_inline(), once done by btrfs_do_readpage() for ranges beyond i_size. - We're touching blocks that don't belong to the inline extent In the incoming patches, we can have a partial uptodate folio, of which some dirty blocks can exist while the page is not fully uptodate: The page size is 16K and block size is 4K: 0 4K 8K 12K 16K | | |/////////| | And range [8K, 12K) is dirtied by a buffered write, the remaining blocks are not uptodate. If range [0, 4K) contains an inline data extent, and we try to read the whole page, the current behavior will overwrite range [8K, 12K) with zero and cause data loss. So to make the behavior more consistent and in preparation for future changes, limit the inline data extents read to only zero out the range inside the first block, not the whole page. 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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| README | ||
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.