d9891ae28b
The index_cnt field of struct btrfs_inode is used only for two purposes: 1) To store the index for the next entry added to a directory; 2) For the data relocation inode to track the logical start address of the block group currently being relocated. For the relocation case we use index_cnt because it's not used for anything else in the relocation use case - we could have used other fields that are not used by relocation such as defrag_bytes, last_unlink_trans or last_reflink_trans for example (among others). Since the csum_bytes field is not used for directories, do the following changes: 1) Put index_cnt and csum_bytes in a union, and index_cnt is only initialized when the inode is a directory. The csum_bytes is only accessed in IO paths for regular files, so we're fine here; 2) Use the defrag_bytes field for relocation, since the data relocation inode is never used for defrag purposes. And to make the naming better, alias it to reloc_block_group_start by using a union. This reduces the size of struct btrfs_inode by 8 bytes in a release kernel, from 1056 bytes down to 1048 bytes. Reviewed-by: Qu Wenruo <wqu@suse.com> Signed-off-by: Filipe Manana <fdmanana@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 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.