ZSTD compressed kernel.

[cedws]

Is your feature request related to a problem? Please describe.
No problem.

Describe the solution you'd like
As far as I can tell, the initrd is currently XZ compressed. I checked this by mounting the boot partition of clear-26430-live.img, navigating to /EFI/org.clearlinux/, and running binwalk kernel-org.clearlinux.native.4.19.2-662 (I think this is the initrd...), which displayed:

DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
0             0x0             Microsoft executable, portable (PE)
17841         0x45B1          xz compressed data
7703056       0x758A10        xz compressed data
7704684       0x75906C        Unix path: /arch/x86/boot/compressed/kaslr_64.c!?

Instead, it could be compressed with ZSTD to yield faster boot times.

Describe alternatives you've considered
I think ZSTD was only recently supported, so LZ4 is an alternative compression option.

Additional context
None.

[bryteise]

That's the kernel, generally our installations/images don't use an initrd unless required (encrypted rootfs for instance).

[cedws]

Ah okay, I thought having an initrd was universal. Since this is compressed with XZ, can other algorithms be used? I had a look and found this relevant patch for ZSTD support.

[bryteise]

@thiagomacieira has looked at using zstd more in the distro I think, any thoughts here?

[fenrus75]

the patch in question is interesting but not quite merged upstream yet... we'll need to keep an eye on it as it matures

…

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[thiagomacieira]

We should benchmark it. Zstd does decompress faster which could help in our objectives for fast boot times. It does compress less than Xz, but given the file sizes in question, it shouldn't affect regular SSDs.

Slow devices (eMMC and SD cards) may want to opt to Xz to minimise I/O.

[ms178]

FYI, the relevant kernel patch series was revised one month ago: http://lkml.iu.edu/hypermail/linux/kernel/1811.1/02341.html

[puneetse]

Just adding a marker here that the ZSTD patch hasn't been merged upstream yet.

[romulasry]

Update?

[romulasry]

https://www.phoronix.com/forums/forum/software/general-linux-open-source/1186412-linux-5-8-rc1-arrives-as-one-of-the-biggest-releases-of-all-time?p=1186528#post1186528

"Still no zstd support for kernel or initrd. Sigh. "

Both of those would be nice to have.

[romulasry]

xanmod made one, here are the patches: https://sourceforge.net/projects/xanmod/files/patches/linux-5.7.y-xanmod/kernel_zstd/

[romulasry]

Now That The Linux Kernel Can Be Zstd-Compressed, The Next Step Is The Firmware
https://www.phoronix.com/scan.php?page=news_item&px=Zstd-Firmware-Compress-Patch

[romulasry]

With Linux 5.9 comes the ability to compress the Linux kernel image / initrd with Zstd
https://phoronix.com/scan.php?page=news_item&px=Linux-Zstd-Compression-Close

Source: https://www.phoronix.com/scan.php?page=news_item&px=Zstd-Firmware-Compress-Patch

[romulasry]

Now that it is updated, it just needs to be compressed with zstd. Great job.