RFE: enable zram support

Describe your issue

What's the expected behaviour?

I'm not sure what process there is to request additional kernel knobs ; more rationale at the end of the post.

main/linux-postmarketos-allwinner/config-postmarketos-allwinner.aarch64 would have CONFIG_ZRAM=m

What device are you using?

pine64-pinephone (2GB version)

On what postmarketOS version did you encounter the issue?

• edge (master branch)
• stable (v20.05 branch)

On what environment did you encounter the issue?

Phone environments

• Phosh
• Plasma Mobile
• Sxmo

Other

• No environment
• GNOME
• KDE Plasma
• Kodi
• MATE
• Shelli
• Sway
• Weston
• Xfce4
• fbkeyboard
• i3wm

How did you get postmarketOS image?

• from https://images.postmarketos.org
• I built it using pmbootstrap
• It was preinstalled on my device

Additional information

Some more rationale:

zram is a mechanism to make a block device backed by compressed ram.

A common usage pattern nowadays is swap on zram, which basically means that paged out memory will be compressed and still in ram.

It may look a bit weird but most memory are fairly compressible and this is still very good latency, so when used appropriately it allows e.g. in my case building memory hungry (c++) apps on devices with limited memory but in general it can be seen as just freeing a bit more memory for page cache or whatever you want to use it for.

alpine (in edge/community) has zram-init (and zram-init-openrc) packages that can help using zram; default use it as swap device and tries to mount extra devices to /tmp and /var/tmp but that's easy enough to tune in /etc/conf.d/zram-init

It's also pretty straightforward to use with zramctl (util-linux), e.g.:

# modprobe zram
# zramctl -f -a zstd -s 1G
/dev/zram0
# mkswap /dev/zram0
(priority helps if you have multiple swap devices)
# swapon -p 32767 /dev/zram0
# zramctl
NAME       ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 zstd            1G   4K   58B    4K       4 [SWAP]
(... after a while... Not very convincing I'll admit, would need to sample
 during some memory hogging compilation or something... But at least the
 compression ratio is very good!)
# zramctl
NAME       ALGORITHM DISKSIZE  DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 zstd            1G 24.8M  5.7M  6.3M       4 [SWAP]

(FWIW, fedora IoT uses 50% of the device's ram as zram device size for swap enabled by default; folks seem happy with it)