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This only affects kernel image compression, not any other xz usage. Desktop kernels on x86-64 are already around 60 MiB. Using a dictionary larger than 32 MiB should have no downsides nowadays as anyone building the kernel should have plenty of RAM. 128 MiB dictionary needs 1346 MiB of RAM with xz versions 5.0.x - 5.6.x in single-threaded mode. On archs that use xz_wrap.sh, kernel decompression is done in single-call mode so a larger dictionary doesn't affect boot-time memory requirements. xz >= 5.6.0 uses multithreaded mode by default which compresses slightly worse than single-threaded mode. Kernel compression rarely used more than one thread anyway because with 32 MiB dictionary size the default block size was 96 MiB in multithreaded mode. So only a single thread was used anyway unless the kernel was over 96 MiB. Comparison to CONFIG_KERNEL_LZMA: It uses "lzma -9" which mapped to 32 MiB dictionary in LZMA Utils 4.32.7 (the final release in 2008). Nowadays the lzma tool on most systems is from XZ Utils where -9 maps to 64 MiB dictionary. So using a 32 MiB dictionary with CONFIG_KERNEL_XZ may have compressed big kernels slightly worse than the old LZMA option. Comparison to CONFIG_KERNEL_ZSTD: zstd uses 128 MiB dictionary. Link: https://lkml.kernel.org/r/20240721133633.47721-14-lasse.collin@tukaani.org Signed-off-by: Lasse Collin <lasse.collin@tukaani.org> Reviewed-by: Sam James <sam@gentoo.org> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Emil Renner Berthing <emil.renner.berthing@canonical.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: Joel Stanley <joel@jms.id.au> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Jubin Zhong <zhongjubin@huawei.com> Cc: Jules Maselbas <jmaselbas@zdiv.net> Cc: Krzysztof Kozlowski <krzk@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Rui Li <me@lirui.org> Cc: Simon Glass <sjg@chromium.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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.