Swap, ZRAM, Zswap and Hibernate on NixOS

eccgecko

Thanks for this. So weird though - I literally spent the better part of the weekend reading and learning all about the differences between zram and zswap and ultimately deciding to switch out my previous zram config for zswap on my NixOS system! So seeing this pop up on my hackernews feed felt a bit spooky…

gucci-on-fleek

I agree with everything else here, but swap files on btrfs should probably be avoided whenever possible [0]. [0]: https://btrfs.readthedocs.io/en/latest/Swapfile.html

seabrookmx

I've had good luck using zswap+zstd on Ubuntu 26.04. I have a Framework 13 (AMD) with 16GB, and have a 16GB swap file configured (ext4 root partition). I had planned to upgrade the machine to 32GB of RAM but I don't really feel it's necessary at this point. Which is obviously great given the current RAM costs!

linsomniac

I also just recently enabled zswap on my NixOS setup, it's been working fine. I have 32GB of RAM and 64GB of swap, so I really don't need it, but it hasn't hurt. I was expecting some problems with my switch to NixOS back in June, but it's been just superb. Even things like building deb packages for my Ubuntu 26.04 machines at work have not been a problem at all. I had dabbled with NixOS for a year or two before making the switch and had some familiarity with the nixlang and various concepts (SOPS, age, flakes). But, what really smoothed out the switch was using Claude Code to develop the NixOS configs. Everything is easy to do that way, and any issues are easy to back out.

correct_horse

Not on nixOS, but I thought I would weigh in on my preferred value for swappiness. 0. For some reason when I have a month of uptime (and I suspend once a day), doing anything with the desktop environment for the first time in a few hours causes a micro stutter for maybe 100ms, as if having to swap out from disk. Turning swap off and on again (meaning no pages are swapped to disk anymore) immediately fixes it. Opening a new tab, pressing the super key even performing certain actions in a video game cause the stutter. I know the internet tells me that 0 isn't a good value, but my computer becomes noticeably worse to use even with a swappiness of 5. I have enough RAM for anything I want to use this computer for, so swap is just for suspend for me.

teravor

whether to use zram or zswap depends on what your intentions are, hibernation doesn't matter (use priority) if your intention is to have enough compressed ram such that you never reach the limit (compression ratios are usually around 3 with zstd) you can allocate over 100% of your ram in zram. then have 100% of your ram as a swap partition for hibernation. this works extremely well but should you exhaust your zram swap serious problems may begin. zswap will be using your SSD and putting wear on it and also imposing latency spikes on old page access, only makes sense if you are certain your swap usage may spike too high in my opinion.