How much swap?

Don't even bother with a SWAP partition. Create an empty file on your / partition so you can grow/shrink it as needed.

    
did if=/dev/zero of=/SWAP bs=1024m count=4
mkswap /SWAP
swapon /SWAP

  

On a desktop or especially laptop case, it should be equal to (or larger than) your RAM if you use hibernation (as RAM gets copied to swap during hibernation)

On my server, I set it up to be 2GBs, mostly arbitrarily. Right now it's at 500MB, but my main memory is also only 600-800MB full out of the total 4GBs available, so I'm not running out of RAM anytime soon.

Swap behavior seems to have changed a while ago, so consider reading https://chrisdown.name/2018/01/02/in-defence-of-swap.html on how it works right now. Hell, even that might be outdated nowadays. Up to date info on how swap works really seems hard to come by.

The 2× recommendation is indeed way old, it stems from a time when computers had 1 or 2 GB of RAM or even less. Nowadays, if you have 16GB of RAM I'd say you're not going to need it (in most use cases).

Chances are your RAM will rarely get so full that your system will need to swap to disk, it's probably going to clear buffer/cached data first. This is data kept in RAM that's not actively used by the system but might be useful soon.

If your RAM does run full you either have some very specific application that demands it (then you probably already know the importance and hopefully wouldn't ask internet randos) or you have a memory leak - that's a problem and I don't believe swapping helps in this case. It's way too slow for that.

If you run VMs and reserve RAM for each those considerations might change.

Personally I don't think swap partitions are particularly useful any more, certainly not 2× your RAM. If you ever want to suspend your system, then it needs to store all your RAM content to disk and it will use your swap for it, so 1× your RAM would be required. But with modern systems and SSDs booting only takes seconds, so I don't think suspend to disk has much utility.

For me swap files are a good compromise. But if a system with 16GB starts swapping, something is not going well.

I believe the swap partition is also used when hibernating. So when you use hibernate you need at least equal swap space as memory size.

As most have pointed, the “always 2x” rule doesn’t have that much of relevance in 2023 as most computers now has more than 4GB of RAM. I would only use that much of a swap when using a low hardware.

For desktop, I would never go swapless, though. In the event of memory pressure, swap would still help in that situation so that OOM Killer do not kick off and unintentionally kill my working process. Plus it helps that Linux can move the least used data to the swap and use the RAM for filesystem cache.

So my rule of thumb, for desktop: If RAM < 8GB: Swap == 2x RAM If RAM => 8GB: Swap == 1x RAM

For servers, I think it depends on the workload. I keep a small amount, like probably 50% of RAM or less. But for stuff like Redis, it doesn’t make sense to have swap. You want to ensure that everything is in the memory.

There's people who make dumb arguments that go "but what if you run out of ram?" And then someone else says "I have enough ram" and then someone else goes "but what if you run out of ram?"

I have a small amount of swap, a few gigs, and enough memory for the application. Moreover I also have my swappiness set to 0 because I don't want stuff swapped out of memory. If I need more memory I need more memory.

I think it's better to think about what swap is, and the right answer might well be zero. If you try to allocate memory and there isn't any available, then existing stuff in memory is transferred to the swap file/partition. This is incredibly slow. If there isn't enough memory or swap available, then at least one process (one hopes the one that made the unfulfillable request for memory) is killed.

If you ever do start swapping memory to disk, your computer will grind to a halt.

Maybe someone will disagree with me, and if someone does I'm curious why, but unless you're in some sort of very high memory utilization situation, processes being killed is probably easier to deal with than the huge delays caused by swapping.

Edit: Didn't notice what community this was. Since it's a webserver, the answer requires some understanding of utilization. You might want to look into swap files rather than swap partitions, since I'm pretty sure they're easier to resize as conditions change.