[dev] consider zram / zswap

[ihrapsa]

This is a kind of swap that resides on RAM in a compressed form. It will make swapping and ram usage more efficient and it will increase the lifespan of the sd card as well.

Resources:
https://openwrt.org/packages/pkgdata/zram-swap
https://openwrt.org/packages/pkgdata/kmod-zram
https://forum.openwrt.org/t/retracted-compressed-memory-this-project-is-officially-retracted-take-note-about-its-future/49076
https://forum.openwrt.org/t/mounting-swap-on-zram-with-discard/48451
https://forum.openwrt.org/t/possible-to-use-zswap/8916/6
https://stackoverflow.com/questions/24467604/swapon-failed-trying-to-enable-zram

Interesting read:
https://haydenjames.io/linux-performance-almost-always-add-swap-part2-zram/
https://ikarus.sg/using-zram-to-get-more-out-of-your-raspberry-pi/

Building:
kmod-zram kmod-lib-lzo (this is selected by default) kmod-lib-lz4 kmod-lib-zstd
Kernel config:
zswap zbud z3fold

Enabling zswap:
either:
opkg install zram-swap - will allocate half of ram size to zram0
echo 1 > /sys/module/zswap/parameters/enabled; in /etc/rc.local (if not enabled by default in kernel)
or

##inside rc.local

swapoff /dev/zram0;
echo 1 > /sys/block/zram0/reset;
echo lzo > /sys/block/zram0/comp_algorithm              
echo 60M > /sys/block/zram0/disksize;
echo 1 > /sys/module/zswap/parameters/enabled;       #seems to be enabled by default
mkswap /dev/zram0;
swapon -p 5 /dev/zram0;

#echo lz4 > /sys/module/zswap/parameters/compressor;
#echo z3fold > /sys/module/zswap/parameters/zpool;
#echo 20 > /sys/module/zswap/parameters/max_pool_percent;
#echo 75 > /proc/sys/vm/swappiness;

[thomsonOZ]

Updated to my KlipperWRT, will review the performance in next few days.

[ihrapsa]

Updated to my KlipperWRT, will review the performance in next few days.

hmm... Thanks, but actually I configured KlipperWrt as default with zram-swap. I tried experimenting with different compression algorithms and ram sizes as well as zswap (which seems to be a more efficient way of using ram) but that zram-swap package/script configures everything depending on the amount of ram you have and I stuck with that. If you manage to get better performance with a different configuration please share 🙂