Chris Down

Depends on your usage patterns. On 8GB I gave it (ZRAM) between 512MB to 768MB RAM, and later on just using whatever values for the relevant sysctls AntiX was using(or their scripts created dynamically during setup/startup) at the time. It isn't just vm.swappiness, there are others, and they changed, or got removed, and replaced by others, over the years. And all of them sort of interwoven, influencing each other via what's happening in vm-subsystem. Can have bad feedback loops if you do it wrong, and be counterproductive. So you have to experiment, and measure with different settings, for what you're running.

Where measure can be anything from htop/atop over https://github.com/cdown/psi-notify , to https://github.com/noiseonwires/memory-pressure and so on.

To understand what these sysctls are about, how they are related to each other, and to ZRAM, I'd recommend reading, or at least skimming https://chrisdown.name/2018/01/02/in-defence-of-swap.html , https://chrisdown.name/2019/07/18/linux-memory-management-at-scale.html , https://linuxblog.io/linux-performance-almost-always-add-swap-space , https://linuxblog.io/linux-performance-almost-always-add-swap-part2-zram , https://linuxblog.io/linux-performance-no-swap-space , https://linuxblog.io/running-out-of-ram-linux-add-zram , https://github.com/ValveSoftware/SteamOS/issues/899 , https://lonesysadmin.net/2013/12/22/better-linux-disk-caching-performance-vm-dirty_ratio , https://github.com/CachyOS/CachyOS-Settings/pull/19 ,…

You're right, I probably should have said "some operating systems". I was generalizing based on my own education, which used Linux. I believe Windows does not do this either, but I'm not sure how many OS 101 classes teach Windows kernel :)

> The advantage is that you find out if you don't have enough memory when you make the system call to request it, not by having the program killed.

I wonder how much of an advantage this is. Memory availability is constantly in flux, and Linux at least, goes to great lengths to reclaim memory before invoking the OOM killer, which is a last resort. What if memory frees up immediately after the application gets the error return, but before the app touches it?

I'd trust the kernel more to manage this than applications themselves, because the kernel can make much better decisions on how to juggle things (evicting caches and whatnot). Plus, we all know how well we all test our error handling paths :)

> (It may be time for paging out to disk to go away. It's a huge performance hit. Mobile doesn't do it. And RAM is so cheap.)

In case anyone is interested in learning more, this is an excellent article discussing the nuances of paging to disk: https://chrisdown.name/2018/01/02/in-defence-of-swap.html

Re: mobile, does Android disable paging file mappings to disk, which happens even if swap is disabled? (Swap only affects anonymous mappings).

>You have a buggy program.

As in memory leak? No.

> Zswap has been available for quite a while.

Zsawp is not Zram, which is a distant relative of the macOS on-the-fly compression I was talking about. Zram is buggy and still advised against regular use (https://www.reddit.com/r/AsahiLinux/comments/1i3mdrw/comment/m7plkkx, https://chrisdown.name/2026/03/24/zswap-vs-zram-when-to-use-what.html). Zsawp itself is enabled by default in Asahi.

Zram and Zsawp are mutually exclusive on Linux. On macOS, both concepts coexist – except macOS is able to compress individual memory pages (https://news.ycombinator.com/item?id=38300432) on the fly. Zram is a compressed RAM block device with a hard capacity limit.

There is really no comparison here at this point. macOS is vastly superior in that regard.

I have some questions.

I started reading about systemd-oomd, then followed the link to its manpage (at https://www.man7.org/linux/man-pages/man8/systemd-oomd.8.html) then followed a link from there to this page: "In defence of swap: common misconceptions" at https://chrisdown.name/2018/01/02/in-defence-of-swap.html).

The first line of the tl;dr is: "Having swap is a reasonably important part of a well functioning system. Without it, sane memory management becomes harder to achieve."

Now, afaik linux as a kernel is pretty much designed to have swap memory and really not meant to be ran without it. Except disabling swap is required to run kubernetes, so much so that the kubelet will plain refuse to start if it detects swap memory enabled.

Why?

Most people think of swap as "emergency memory in case I run out of memory" and while it's true that it can get used in this way, it usually serves a much more critical purpose in your OS's ability to reason about and use memory.

For a good article on why this is true for Linux: https://chrisdown.name/2018/01/02/in-defence-of-swap.html

I believe that most operating systems are going to make use of memory in a similar manner.

With that said, I'll turn off swap on devices that have unreliable storage. (Anything using an SD card)

Fair points overall. I think KSM is still useful and worth the overhead for things like sprawling browser tabs and densely deployed microservices.

I disagree that swap is only (or even primarily) for situations where you're running out of memory, though. It is useful for reducing I/O contention and improving memory utilization by replacing underutilized pages with file cache when it makes sense to do so. See this for more details: https://chrisdown.name/2018/01/02/in-defence-of-swap.html