zram: Use "ram / 2" instead of hardcoded value

[technobirb]

describe the request

Is there a reason zram-size is calculated & hard-coded at install time, instead of using ram / 2? What if the user's RAM size changes later?

Also I wish there is a "default" option for compression-algorithm (which just corresponds to not writing anything for it) to track kernel defaults.

[h8d13]

It does use ram / 2 :)

ram_kb = SysInfo.mem_total()
# Convert KB to MB and divide by 2, with minimum of 4096 MB
size_mb = max(ram_kb // 2048, 4096)

About your second point it is a fair one !

[technobirb]

What I mean is that it can just write zram-size = ram / 2 instead of calculating it and writing something like zram-size = 8192 in the config.

zram-size=
Sets the size of the zram device as a function of MemTotal, available as the ram variable.

[h8d13]

You are 100% correct, I did not see this is actually already default: Defaults to min(ram / 2, 4096). From https://man.archlinux.org/man/zram-generator.conf.5

So basically you could also just not write anything

[technobirb]

So basically you could also just not write anything

Hang on, the default says min not max, so it caps the zram at 4GiB. 😅

[technobirb]

@svartkanin As said in the previous comment, the default is min(ram / 2, 4096) not max(ram / 2, 4096):

By default the zram device will use half the RAM size but no more than 4 GiB: e.g. it will create a 2 GiB zram device if you have 4 GiB of RAM, but only a 4 GiB zram device if you have 8 GiB of memory or more.

https://wiki.archlinux.org/title/Zram#Using_zram-generator

While this commit's intention is max(ram / 2, 4096):

• Systems with 8 GB RAM or less will get 4096 MB zram
• Systems with more than 8 GB RAM will get half their RAM as zram

[svenstaro]

Why do you highlight me?

[svartkanin]

My change will remove the size being written to the configuration and use whatever default zram generator provides

[technobirb]

Why do you highlight me?

Oops so sorry wrong user name... Comment edited.

[technobirb]

I see, yeah. My second thought about the current max(ram / 2, 4096): What if the user's RAM is small, e.g. 1GB?

Even a /dev/zram0 of 200% RAM is not unreasonable if the compression ratio is at least 2:1. However, it's possible a system can get "stuck" in a kind of swap thrashing similar to conventional swap-on-drive

assuming that zstd only achieves a conservative 1:2 compression ratio (real world data shows a common ratio of 1:3)

Fedora currently use zram-size = min(ram, 8192). Checked with Live ISO.

https://fedoraproject.org/wiki/Changes/SwapOnZRAM#Why_not_a_bigger_zram_device?
https://wiki.archlinux.org/title/Zram#Usage_as_swap
https://fedoraproject.org/wiki/Changes/Scale_ZRAM_to_full_memory_size

[svartkanin]

The stance of archinstall hs mainly been to stuck to defaults where'er possible to avoid opinionated implementations