Add ZRAM kernel module

[joshbowyer]

Module or flag. This is pretty standard on ChromeOS as well as most Linux distros now (it has been added to Mobian for Pine devices too)

[SolidHal]

Seems like it would give us some nice performance improvements on these low-ram systems. Could users with ChromeOS report how large of zram partitions are used on 2GB and 4GB models?

[joshbowyer]

I dont use ChromeOS but on Mobian (Debian for Pine) we generally set it to 50% and all cores (4), and it works very well

[SolidHal]

CONFIG_ZRAM was actually already enabled on the armhf kernel. Now enabled on the arm64 kernel as well. Next is to setup the userspace config to take advantage of it.

[joshbowyer]

It isnt on my install and I installed v1.1... to enable in userspace install zramswap and edit /etc/defaults/zramswap

[SolidHal]

PrawnOS/kernel/resources/armhf/config

Line 1478 in f845964

CONFIG_ZRAM=y

shows it is built in to the kernel. Its not a module, so it won't show up in lsmod. Actually, nothing is a module right now. on my veyron-speedy, I see /dev/zram0 which further confirms it is enabled.

By "on all cores (4)" are you saying there is a zram device per core?

[joshbowyer]

Yes, it utilizes all cores which is optimal, otherwise you only get 1/4 the swap capacity/processing.

Ill have to double check the exact error Im getting because when I started it it screamed about the module not existing...

[SolidHal]

ah, so you are talking about cat /sys/block/zram0/max_comp_streams not the number of zram devices to create? From https://www.kernel.org/doc/html/latest/admin-guide/blockdev/zram.html it looks like it automagically creates the right amount of compression streams

[joshbowyer]

Im not sure about how it translates to the /sys blocks, but as far as the config itself those are the variables/values we found to work best. (Im not a dev, Im a linux admin who tries to help as much as he can lol, so sorry if Im missing an obvious link here)

[graves]

Zram takes a parameter to set the number of devices it creates, the default is 1 which is why you only see /dev/zram0 created.

So you'd either need to build it as a module and load it with:

modprobe zram num_devices=4

or add the parameter to the kernel parameters when you build the kernel.

[SolidHal]

@graves thanks but my confusion is around if we want a zram device per cpu or if max_comp_streams is what we want per cpu.
I'm leaning towards max_comp_streams since the documentation mentions it now automatically sets max_comp_streams based on the number of cpus