In defence of swap: common misconceptions

On windows I have found it necessary to disable swap to keep myself efficient. Many times Ive had applications decide to allocate massive amounts of memory and then it leads to my system slowing down with tons of swap activity. In nearly all cases, I didn't want my system to try its best to handle these massive memory requests but rather it should have just killed the offending application. Often in these failure scenarios the swap goes nuts and my computer becomes unresponsive that it takes a long time to even get to kill the bad actor.

Thus I disabled swap and I never had these unresponsive issues. I run with 32GB of ram so generally well behaved applications never run into memory issues.

Some applications that would cause issues would be too many VirtualBox instances that use more than available memory. A text editor that chocks trying to open a >1GB text file (looking at you, the new JS-based editors.)

So, in other words, if you have enough memory for your workload that you won't run out, there's no benefit to having swap space (i.e. you've wasted money on memory you don't need).

But if you DO have swap space, there won't be a performance hit (at least not under Linux) because it will only swap out some rarely used pages and then sit there doing nothing.

So, in the general case, it's better to have it and not need it than need it and not have it.

I have an older Chromebook (c720), which is really quite memory starved (2GB RAM), and have experienced ChromeOS completely frying the SSD simply through prolonged tab-heavy swapping.

Now, I've replaced the SSD and installed a non-Google Linux distro, and would like to limit the amount of swapping Firefox can do.

I had been planning to simply use cgroups' memory features to limit the amount of memory consumed by Firefox processes, but if I am to understand the article (which I admit I didn't read in full detail), I should also be able to tune swapping to limit the actual amount of swapping that takes place, avoiding a drastic uptick in SSD wear whenever open too many tabs.

That, and perhaps a Firefox extension that suspends background tabs in memory (which I've used before with a certain amount of effectiveness in the pre-WebExtension days).

This is an informative and well written article, but seems incomplete in this day and age. In public cloud environments, network attached storage is far more prevalent, so the swap story may be different there (I honestly don't know though). Since the author works at Facebook, he probably lacks experience in this regard.

Even for those who understand this well, it's historically been really hard to coerce the Linux kernel into applying the right swap policies to your application.

As the author notes much of this has been improve by cgroups, and there's always been big hammers like mlock(), even with those things it can be hard to prevent memory thrashing in extreme cases. I've seen swap disabled completely by people who understood how it worked as a last result because of that.

It's always seemed to me that this was mainly a problem of the kernel configuration being too opaque. Why can't you configure on a system-wide basis that you can use swap e.g. only for anonymous pages and for nothing else?

Similarly it would be nice to have a facility for the OOMkiller to call out to userspace (it would need dedicated reserved memory for this) to ask a configured user program "what should I kill?". You might also want to do that when you have 10G left, not 0 bytes.