Arch Linux

xerxes_

Member

Registered: 2018-04-29

Posts: 815

zswap: compressor lz4 not available

Why I see that error in journalctl (red, -p3) after update to arch linux kernel 6.3.4 from 6.3.2:

zswap: compressor lz4 not available, using default zstd

Is lz4 not supported any more?

Last edited by xerxes_ (2023-05-26 09:01:38)

seth

Member

Registered: 2012-09-03

Posts: 59,882

Re: zswap: compressor lz4 not available

Switch to zstd default:
https://gitlab.archlinux.org/archlinux/ … _1052_1054

https://wiki.archlinux.org/title/zswap# … _algorithm

Can you still https://wiki.archlinux.org/title/Zswap#Using_sysfs ?

modinfo lz4
lsinitcpio /boot/initramfs-linux.img | grep lz4

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xerxes_

Member

Registered: 2018-04-29

Posts: 815

Re: zswap: compressor lz4 not available

Is this zstd compression better/faster, so is that switch?
It has many level of compression (1-22), default 3 says man page, but I don't know how does it apply to this version in kernel.

I didn't know what level of compression was used for lz4.
Can level of compression be set somewhere? How can I find out what is current level of compression?

What is default compression for current lts kernel? If I delete lz4 from boot params for lts, will be zstd used by default?

Last edited by xerxes_ (2023-05-26 09:25:26)

seth

Member

Registered: 2012-09-03

Posts: 59,882

Re: zswap: compressor lz4 not available

I've no idea why the default was changed. Historically zstd has better but slightly slower compression.
You didn't answer whether you can still change the compressor at runtime.

What is default compression for current lts kernel?

zgrep -i zswap /proc/config.gz # when booting the lts kernel

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xerxes_

Member

Registered: 2018-04-29

Posts: 815

Re: zswap: compressor lz4 not available

For now, for lts kernel lz4 is still default zswap compressor.
And yes, I can still change the compressor at runtime, but I will leave it as it is for now and see... I've just remove force any compressor from boot params.

It looks like on kernel 6.3 also zsmalloc is the default instead of z3fold as zswap zpool (which is still on lts kernel), at least in kernel config, but I have set in boot params z3fold, so it thankfully does not apply to me (maybe because zpool can't be changed at runtime).

Last edited by xerxes_ (2023-05-26 19:10:32)

seth

Member

Registered: 2012-09-03

Posts: 59,882

Re: zswap: compressor lz4 not available

And yes, I can still change the compressor at runtime

Did you see the 1st wiki paragraph I linked?
Did you add lz4 to the initramfs MODULES?

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xerxes_

Member

Registered: 2018-04-29

Posts: 815

Re: zswap: compressor lz4 not available

Yes, I saw that links, but I want to check that zstd compression on new kernel under my loads and try to see the difference. If I will be unhappy I will switch back to lz4.
I also think about this new zpool zsmalloc default, but it's complicated and I don't understand how it work, so I wont try it for now. Also checking one thing at a time.