Clarifying the ZRAM Implementation: dom0 vs. AppVMs

[queen]

Continuing the discussion from Memes about Qubes OS:

@alimirjamali

I am working with @Atrate and others to make this possible:
Assigning then unassigning ZRAM devices in Qubes Devices widget causes system lockup · Issue #9255 · QubesOS/qubes-issues · GitHub

@queen

What is the current status of the ZRAM project?

@Atrate

In my experience ZRAM works well, though you have to install it yourself for now.

Yes, I’m now using zram inside my AppVMs. It works.
But as I understand the project that alimirjamali linked to, zram is set up within dom0. Or did I misunderstand?

[Atrate]

You can (and in my opinion should) set up zram in both AppVMs and dom0.

[Atrate]

Also see

Consider installing the zram generator package by default in Qubes templates

[corporateblush]

How To Set And Use ZRAM swap

I’d like to remind that zram has a cost when used and it’s not a magic bullet that generates usable memory out of nowhere. It reserves some memory where it’s running, so it means your system has less memory to run, and it compresses unused memory on the fly when you run out of memory. This is setup as a swap device with a higher priority than a disk backed swap, so memory goes in there. The CPU cost is real and introduce lag that could be higher than swapping to a fast SSD. I tend to o prefer …

I find it good, when having plenty of RAM, to also prevent SSD wearing off this way.

[queen]

Where do you use ZRAM: AppVM and/or dom0?

[corporateblush]

In all Linux qubes, while not any swap in dom0 since assigned enough of RAM for otherwise not heavy loaded dom0 actions anyway.

For example:

[user@personal ~]$ swapon --show
NAME TYPE SIZE USED PRIO
/dev/xvdc1 partition 1024M 0B -1
/dev/zram0 partition 732M 61.2M 100
[user@personal ~]$ cat /sys/module/zswap/parameters/enabled
N

Meaning, no hibernation, but sleep is enough. It’s probably reflex from the past where hibernation doesn’t work with Qubes reliably anyway. In addition I always strongly disliked hibernation in any kind of shape and form. Walt Disney obviously disagreed with me.