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35478d053a
In btrfs_lookup_bio_sums() if the bio is pretty large, we want to start readahead in the csum tree. However the threshold is an immediate number, (PAGE_SIZE * 8), from the initial btrfs merge. The meaning of the value is pretty hard to guess, especially when the immediate number is from the times when 4K sectorsize was the default and only CRC32C was supported. For the most common btrfs setup, CRC32 csum and 4K sectorsize, it means just 32K read would kick readahead, while the csum itself is only 32 bytes in size. Now let's be more reasonable by taking both csum size and node size into consideration. If the csum size for the bio is larger than one leaf, then we kick the readahead. This means for current default btrfs, the threshold will be 16M. This change should not change performance observably, thus this is mostly a readability enhancement. Reviewed-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: Qu Wenruo <wqu@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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 Restructured Text 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.