[Aardwolf]

In defence against swap on my personal computer:

-PCs have a lot of RAM now

-When you allocate that much memory it's usually a bug in your own code like a size_t that overflowed. I never saw programs I would actually want to use try to allocate that much

-When using swap instead of ram, everything becomes so slow that you're screwed anyway. The UI doesn't even respond fast enough to kill whatever tries to use all that memory.

-How common is a situation where you need more memory than your ram size yet less than ram+swap size in a useful way? Usually if something needs a lot, it's really lot (and as mentioned above not desirable)

-Added complexity of making extra partition

-Added complexity if you want to use full disk encryption

-I do the opposite of using disk as ram: I put /tmp in a ramdisk of a few gigs

-Disks are slow and fast ssd's are expensive so you would't want to sacrifice their space (maybe if this changes some day...)

[mort96]

Regarding the complexity of making an extra partition: I completely agree, having a separate partition for swap is annoying. Luckily, Linux supports swap files; all my systems (where I had to manually set up swap), I just create a file called /swapfile.

I imagine this would solve the full disk encryption complexity too.

[znep]

The reasons I couldn't live happily without swap on my development machine:

- Macbook Pro's don't have a lot of RAM. Still. (Let's not get into that whole discussion as valid as it may be, that is far from the biggest issue I have with current macbooks...)

- Macbook Pro's have no user facing complexity to use swap or to have it encrypted. Heck, they even give you a middle ground as well by default of compressed RAM.

- I have to run a lot of services to run our development stack. Most of the time I'm only using a few but don't want to have to go manually start and stop services all the time. Also, even within a service typically access to most of the memory isn't required for every request. Swap handles this quite well.

- There are parts of our development stack that, simply put, are extremely bloated in terms of memory use. Four gig webpack process, I'm looking at you. Yup, that is ridiculous and should be fixed and maybe there is a fix out there we haven't figured out ... but I don't care, isn't my problem, and I don't have to fight it because it seldom accesses most of that bloated memory so it lives great in swap.

- I like being able to switch to working on something else without having to shut down and restart all the applications I'm using as required for the new task. Swap is a great fit for that. For example, if I have to switch from developing code to analyzing a large Java heap dump, which requires lots of memory, I don't have to go shut everything down, it just quickly gets paged out to swap and comes back when I need it. I don't care if it takes an extra 30 seconds for switch between these two tasks, it already takes much longer than that to load the heap dump regardless.

I think often people give swap a bad name because they never see what it does well for them unless they go looking for it, they only see it when they are asking their machine to do something where the working set is actually too big for memory and blame swap.

That said, no need for swap if you can live fine without it. I just don't think that is good general advice.

[cdown]

> I never saw programs I would actually want to use try to allocate that much

What about applications that have memory-bound performance characteristics? In these cases, saving a bit of memory often directly translates into throughput, which translates into $$$.

This isn't a theoretical, a bunch of services which I've run in the past and currently literally make more money because of swap. By using memory more efficiently and monitoring memory pressure metrics instead of just "freeness" (which is not really measurable anyway), we allow more efficient use of the machine overall.

[IncRnd]

Exactly! Also, the person who goes from 32G of RAM to 256G of RAM is going to run without swap.

[Symbiote]

I have 4GiB swapfiles on the cluster nodes I manage, which have 512GiB RAM.

It's hardly used, around 300MiB at present, probably things like the mail daemon. It's been useful to have a very slow node, which I can SSH into (after 10 minutes) and kill a chosen process, rather than a dead/OOMed node. But I think the difference is marginal, and perhaps 512MiB would have been a more appropriate size for the partition.

(Swappiness is set to 1.)

[IncRnd]

We run without swap, and haven't noticed an issue. Did you see any practical benefit to running swap vs not?

[Symbiote]

Other than a couple of occasions where things have run slowly, giving me time to kill the process I choose, I've not noticed any benefit.

Picking a random machine, there is 600MB of swap used. "top" shows where about 50MB is used (Hadoop daemons, systemd bits) but I don't know what the rest is. I guess it could backfire, since logind is swapped out, and I might want to log in on the serial console if the machine is very busy.