Ubuntu 23.10 Is Maxing Out Zstd Compression For Its Kernel Build

Dimitri John Ledkov of the Ubuntu kernel team has written about some of the improvements made for the default kernel build on Ubuntu 23.10. Ubuntu's Linux kernel build is now using much less disk space, lower RAM use, and much faster initrd generation.

In a blog post today Dimitri John Ledkov sums up the Ubuntu 23.10 kernel benefits as:

- 2x less disk space used (1,417MB vs 2,940MB, including initrd)
- 3x less peak RAM usage for the initrd boot (68MB vs 204MB)
- 0.5x increase in download size (949MB vs 600MB)
- 2.5x faster initrd generation (4.5s vs 11.3s)
- approximately the same total time (103s vs 98s, hardware dependent)


For minimal cloud images that do not install either linux-firmware or modules extra the numbers are:
- 1.3x less disk space used (548MB vs 742MB)
- 2.2x less peak RAM usage for initrd boot (27MB vs 62MB)
- 0.4x increase in download size (207MB vs 146MB)

These improvements come from changing around the Debian packaging for their kernel build. Ubuntu is now pre-compressing their kernel modules and firmware files using the maximum level of Zstd compression, actual Debian files are now uncompressed, assembling the initrd using split CPIO archives, enabling in-kernel module decompression support, and various bug fixing.

More details on these Ubuntu 23.10 kernel improvements can be found via this blog post.