I think the key here is what you mean by using swap. Having a lot of data swapped out is not bad in and of itself - if the machine genuinely isn't using those pages much, then now you have more space available for everything else.
What's bad is a high frequency of moving pages in and out of swap. This is something that can cause your machine to be functionally unavailable. But it is important to note that you can easily trigger somewhat-similar behaviour even with swap disabled, per my previous comment. I've seen machines without swap go functionally unavailable for > 10 minutes when they get low on RAM - with the primary issue being that they were grinding on disk reloading dropped executable pages.
I agree that in low memory situations killing off something ASAP is often the best approach, my main point here is that relying on the Linux OOM killer is not a good way to kill something off ASAP. It kills things off as a last resort after trashing your machine's performance - userspace OOM killers in concert with swap typically give a much better availability profile.
In a situation where a bunch of memory is being used by something that is literally not needed and won’t be needed in a hurry, then it’s not a big deal.
In my experience though, it’s just a landmine waiting to explode, and someone will touch it and bam useless and often difficult to fix machine, usually at the most inconvenient time. But I also don’t keep things running that aren’t necessary.
If someone puts swap on something with sufficiently high performance, then obviously this is less of a concern too. Have a handful of extra NVMe or fast SSD lying around? Then ok.
I tend to be using those already though for other things (and sometimes maxing those out, and if I am, almost always when I have max memory pressure), so meh.
I’ve had better experience having it fail early and often so I can fix the underlying issue.
What's bad is a high frequency of moving pages in and out of swap. This is something that can cause your machine to be functionally unavailable. But it is important to note that you can easily trigger somewhat-similar behaviour even with swap disabled, per my previous comment. I've seen machines without swap go functionally unavailable for > 10 minutes when they get low on RAM - with the primary issue being that they were grinding on disk reloading dropped executable pages.
I agree that in low memory situations killing off something ASAP is often the best approach, my main point here is that relying on the Linux OOM killer is not a good way to kill something off ASAP. It kills things off as a last resort after trashing your machine's performance - userspace OOM killers in concert with swap typically give a much better availability profile.