Experience has shown me over and over that you just want to feel the limits of the machine hard and fast so you can change what you're asking of it rather than thinking that there is some perf issue or weird bug.
It's the idea that swap is somehow useful that's old. It's not, it never worked right for interactive systems. It's a mainframe thing that needs to die.
Lots of the stuff you're using is backed by disk anyway -- and will be removed from RAM when there's any memory pressure, whether or not you have any swap. If you've got swap then the system can put anonymous pages in it, otherwise it'll need to evict named files more frequently.
Unless you have enough RAM that you're literally never evicting anything from your page cache, in which case swap still doesn't hurt you.
I'll absolutely agree that swapping out part of the working set is unwanted, but most swapping is benign and genuinely helps performance by allowing the system to retain more useful data in RAM. You don't want to get into a state where you're paging code in and out of RAM because there's nowhere to put data that's not being used.
Other random semi-related thoughts:
- Rust having to define a new stdlib to be used in Linux kernel because of explicit allocation failure requirements. Why wasn't this possibility factored in from the beginning?
- Most software nowadays just abstracts memory costs, partly explaining why a word processor that used to work fine with 64mb of RAM now takes a gig to get anything done.
- Embedded development experience should be a requirement for any serious software engineer.
This is phrased in a way that’s a bit more extreme than in reality. Some new features are in the process of being added.
> Why wasn't this possibility factored in from the beginning?
So, there’s a few ways to talk about this. The first is… it was! Rust has three major layers to its standard library: core, alloc, and std. core, the lowest level, is a freestanding library. Alloc introduces memory allocations, and std introduces stuff that builds on top of OS functionality, like filesystems. What’s going on here is the kernel wanting to use the alloc layer in the kernel itself. So it’s naturally a bit higher level, and so needs some more work to fit in. Just normal software development stuff.
Why didn’t alloc have fallible APIs? Because of Linux, ironically. The usual setup there means you won’t ever observe an allocation failure. So there hasn’t been a lot of pressure to add those APIs, as they’re less useful then you might imagine at first. And it also goes the other way; a lot of embedded systems do not allocate dynamically at all, so for stuff smaller or lower level than Linux, there hasn’t been any pressure there either.
Also, I use the word “pressure” on purpose: like any open source project, work gets done when someone that needs a feature drives that feature forward. These things have been considered, for essentially forever, it’s just that finishing the work was never prioritized by anyone, because there’s an infinite amount of work to do and a finite number of people doing it. The Rust for Linux folks are now those people coming along and driving that upstream work. Which benefits all who come later.
Steve has responded to your comment about Rust; to your other comments:
Modern applications do a lot more than old ones. Even if you only use 20% of the features, you probably use a different 20% from any arbitrary other person. You also probably benefit from the OS being able to map everything into virtual memory but only actually load the bits you use :).
And I strongly disagree with your stance on being "serious". I'm sure you don't mean to gate-keep, but we need to teach people where they are rather than giving them hoops to jump through.
In my experience, some of the best software engineers have very little development background. And I say that as someone who implemented 64-bit integer support for the compiler and RTL for a DSP part back in the day. It's useful to have people around with a variety of backgrounds, it's not necessary for everyone to share any particular experience.
As the gas-powered engine people will say: "there's no replacement for displacement" (I wont push the analogy comparing zram to turbocharging but, you know, they both deal with "compression"...)
