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.
Agree. I tried using a swapfile last year-ish, as the internet experts tell you to. I have 64GB of RAM. If I fresh boot and start a few apps I'll be using maybe 16GB RAM + 0GB swap. Then a few hours later I see I'm using 8GB of RAM + 8GB of swap... why? Why did Linux waste IO moving data to disk when there's no memory pressure?
Generally the idea is that regions of memory that aren't being used are swapped out to disk, then other more useful things are brought into memory.
For example: you have a background program that you're not using and in the foreground you're crunching data from disk. In this scenario the most efficient use of your memory is to swap the background program out and pull the disk data into RAM.
But why should it swap things out even when I'm not crunching data and there's no memory pressure? I'd rather everything stay in memory and stay fast, since I have enough RAM.
Maybe not what's happening in your case, but stuff that is in swap will not be moved back to memory unless there's a need for it, so if you did have memory pressure at time 1, which resolved at time 2, then you might still see a lot of swap in use at time 3.
correct_horse · · focus · HN ↗
nvme0n1p1 · · focus · HN ↗
That's why I don't use swap.
franticgecko3 · · focus · HN ↗
For example: you have a background program that you're not using and in the foreground you're crunching data from disk. In this scenario the most efficient use of your memory is to swap the background program out and pull the disk data into RAM.
nvme0n1p1 · · focus · HN ↗
stdbrouw · · focus · HN ↗