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That structure records needed info for block verification (either data checksum pointer, or expected tree block generation). But there is also a boolean to tell if this block belongs to a metadata or not, as the data checksum pointer and expected tree block generation is already a union, we need a dedicated bit to tell if this block is a metadata or not. However such layout means we're wasting 63 bits for x86_64, which is a huge memory waste. Thanks to the recent bitmap aggregation, we can easily move this single-bit-per-block member to a new sub-bitmap. And since we already have six 16 bits long bitmaps, adding another bitmap won't even increase any memory usage for x86_64, as we need two 64 bits long anyway. This will reduce the following memory usages: - sizeof(struct scrub_sector_verification) From 16 bytes to 8 bytes on x86_64. - scrub_stripe::sectors From 16 * 16 to 16 * 8 bytes. - Per-device scrub_ctx memory usage From 128 * (16 * 16) to 128 * (16 * 8), which saves 16KiB memory. Reviewed-by: Filipe Manana <fdmanana@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 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.