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.
It's a broken idea, throughput über alles isn't true of an interactive system, latency matters. There's a calculator app I use every now and then. Linux always thinks it's a good idea to swap it out since I'm not using it all the time, which means that every time I want to calculate something there's lag as it's swapped in again.
Another aspect I'd wonder about for relatively simple tasks is just freeing it from memory and being prepared to pay the cost of loading it again, it's probably already on disk. Latency matters, but it seems there will be limits especially considering the transfer speed and latency improvements we've seen to storage commonly installed in most systems over the past 15 years or so.
Then comes the challenge of deciding what processes/data to free or page, whether that's flagged by the system as it's running or at coding/compile time. And that seems similar to the issue of picking a swap strategy for a distro/OS, which will depend on the user's demands or system, setting a good default and exposing how to change the configuration to a better match if needed.
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.
kryptiskt · · focus · HN ↗
keyringlight · · focus · HN ↗
Then comes the challenge of deciding what processes/data to free or page, whether that's flagged by the system as it's running or at coding/compile time. And that seems similar to the issue of picking a swap strategy for a distro/OS, which will depend on the user's demands or system, setting a good default and exposing how to change the configuration to a better match if needed.