Thursday, 30 May 2019

Re: Supporting LZ4 as initramfs compressor

Am Donnerstag, den 30.05.2019, 11:46 +0100 schrieb Dimitri John Ledkov:
> On Thu, 30 May 2019 at 11:35, Dimitri John Ledkov <>
> wrote:
> >
> > I see a lot of code in livecd-rootfs that tries hard to use lzma
> > compression for the initaller (first-boot) initrd.
> > On the classic, subsequent initrds get rebuild as gzip, and on core
> > lzma persists.
> > I do wonder what compression we should use by default for the
> > installer media, Ubuntu Core, cloud images.
> >
> > Is the rationale for lzma installer initrds still valid? And what
> > was
> > it? Smallest size initrd?
> >
> Note subiquity dropped using lzma for the installer image to improve
> boot speed.
> Which I find confusing from the spreadsheet graphs....
> gzip is fast at kernel, but not initrd
> lzma fast at initrd, but not kernel
> As if lz4 kernel & xz initrd would yield the fastest boot time? That
> sounds counter-intuitive. Unless for initrd, only the compressed size
> matters and initrd decompression time does not matter?
> Measurements until break=bottom is reached would be nice.
> --
> Regards,
> Dimitri.

I initially suggested lz4 support a few years back in LP #1488620. I
do not have insight in all the projects at Canonical/Ubuntu and what is
state of the art regarding compressors. If you ask me today I would
recommend zstd, it is not intended to be as fast as lz4 and comparable
high speed decompressors, but faster than lzma and gzip. I recently
found 7-Zip zstd[1] while looking for a solution that supports zstd on
Windows, may be the graphs in the project repository help you to find a
better solution and learn about recently developed compressors.


Best regards,

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