*8GB of RAM without use of ZRAM or Swap isn’t enough for even most day-to day tasks. MacOS uses swap, which is slower than RAM and incurs precious write-cycles to the SSD. Also, the typical usage of memory by the MacOS is more than twice than on Linux even without any optimizations on Linux side.
ZRAM is a wonderful piece of technology that compresses the inactive section of RAM to increase the amount of available memory on a system. Typically, RAM is compressible upto 4 times using zstd, which is a sweet algorithm that balances compression and speed.
Let’s say you have 16GB of RAM. Let’s dedicate 3/4 of the RAM to zram. Assuming compression ratio of 1:4, we use store, 56 (124 + 8) GB of RAM. If you don’t use swap, your system responsiveness won’t take a hit and your CPU usage will increase by whatever the zram uses to compress and decompress your memory pages. Similarly, for 8GB RAM, we can extend it upto 26 (64+2) GB of RAM.
This isn’t helpful if you’re using the same pages again and again, compressing and decompressing, like running a Large Language model (LLM), video editing or gaming. While editing video or large photo, you will need to have it in memory or very fast SSD to have quick seeking capability. Having it in ZRAM means you will need to compress and decompress it frequently. It won’t be a problem if the file is small. But at some point, you can’t beat physics (and Math in this case). In LLM as well, almost all the weights need to be loaded and used in small amount of time. So if you’re mostly using zram for that, there is large amount of compression and decompression going around.
But if you consider a typical usage, where you load loads of apps in memory but will only be using only couple of them at a time, you can just compress the unused apps and decompress and use it as needed. Typical browsing experiece such as web-browser, word editing, programming, slack, teams, etc. won’t be impacted because you’re most likely using only a small fraction of them at a time.
Configuration
Fine tune some values for zram.
# /etc/sysctl.d/99-vm-zram-parameters.conf
vm.swappiness=200
vm.vfs_cache_pressure=200
vm.page-cluster=0
vm.dirty_ratio=2
vm.dirty_background_ratio=1
vm.watermark_boost_factor = 0
vm.watermark_scale_factor = 125# /etc/systemd/zram-generator.conf.d/01-zram0.conf
[zram0]
# zram with zstd compression ratio is about 1:4.
# 3/4 - zram and 1/4 - apps and system
zram-size = ram * 3
compression-algorithm = zstd