For more than a year it’s been talked about adding an option to support Zstd-compressed Linux kernel images while it looks like that Facebook-backed high performance compression algorithm for kernel images could soon finally be mainlined.
Zstd compression is used elsewhere in the Linux kernel but support for compressing the kernel image with Zstandard hasn’t materialized in the tree. On Friday, developer Adam Borowski sent out a set of 17 patches adding kernel compression for Zstd. In the process, he’s also aiming to drop LZMA1 and BZIP2 compression support for kernel images. He briefly wrote, “As new compressors get invented, they tend to find their way into the kernel, yet we never prune superseded ones. It’s time to do so…BZIP2 is drastically slower than other compressors we have, even when they achieve smaller sizes. It takes more memory, too. And, BZIP2 is not used anywhere else in the kernel — just for booting the kernel itself and the initrd…LZMA1 is redundant with XZ (LZMA2), and unlike the latter, it uses its own copy of code that’s not shared with anything else (some drivers use XZ). Let’s drop it as well.“
Borowski is recommending most kernel images be compressed with XZ while for those concerned about speed, Zstd is the recommendation. There are also other compression algorithms supported but they are used elsewhere or not otherwise deemed appropriate for dropping.
We’ll see where this patch series goes in the post-4.20 kernel world.
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