I never saw any issues doing this, but I learned that linux ideally wants some swap space, which it will use for some kind of housekeeping stuff.
But I've found that even with no/little swap, the system can get into high memory pressure situations (even easier because it can't swap out unused pages of libraries and the like), and still go into a sort of thrashing state even though it isn't swapping.
My main workstation is a Dell XPS15 with 32GB of RAM and I had 8GB of swap on it. About every month the system load would skyrocket even though it had plenty of mem+cache+swap available. If I killed off my browser and slack, load would return to normal, and I could use the system for a few more days or a week before it happened again.
I struggled with this for a year or more, before (for reason's I don't remember), I added another 8GB of swap. Within the next day 80% of the extra swap was used right up. I decided to swapoff that new file and create a 64GB swapfile and just see what happened. It got to around 20-30GB IIRC before it leveled off. And, more importantly, over the next 100+ days I never had that thrashing happen again.
That was with Ubuntu 22.04. I just recently (May-ish) switched over to a NixOS setup with 64GB of swapfile, and it's been very stable.
That's probably not right with today's RAM sizes but I'm not sure what the current rule is. I just go with the Ubuntu installer default but I don't know if that's just a fixed number or computed in some way from amount of RAM available.
Which was always a dumbass rule that made no logical sense.
Like, I remember a time when I had 4 GB of RAM and had my swap set to 8 GB. Then I upgraded to 16 GB of RAM. Theoretically, I shouldn't even need a swap file anymore, since my old setup would max at 12 GB and yet I never had OOM problems, but that "rule of thumb" would dictate that I should increase my swap to 32 GB.
I remember when I first came across this rule when getting into Linux for the first time. If memory serves, I had 256MB of RAM, so I set swap for 512MB, which seems perfectly cromulent.
The other part was that it kinda matched the money you were spending on the machine.
The guy with 128MB of ram could likely afford to spend the extra disk space on a swap partition then the guy stuck with just 32MB.
(They obviously don’t page out, they are just discarded and read again when needed)
But while I don't have any hard data, I imagine that depending on the workload, there can be a punch of pages that are read during initialization, or a one-off workload, and never being read or freed up afterwards.
Just try activating a swap file, and see if it gets any usage, despite memory pressure being low.
Not as big of a problem as it used to be. Both because OOM killer has gotten better and also web servers are such a commodity that remotely cycling them isn't going to cause a outage and is the quickest and cleanest way to get them back into production.
The OOM killer looking at processes and seeing a giant one, using 90% of the physical memory and growing fast and deciding "Oh, that's ok because it is working hard, I'm going to go kill this little tiny thing that hasn't been used recently called sshd". Inoculating sshd against the oom killer is SOP now.
Note that RAM is much, much more expensive than disk space. If I can sacrifice some of the latter to potentially get some of the former, it's usually a nice trade for me.
Even if you have plenty of ram, having swap can help with performance.
Why? Because the OS can page rarely used or seemingly downright unused dirty pages to swap, freeing up precious RAM for caches.
I'd hazard a guess that especially if you run a ton of containers this can help, as there's probably a lot of memory getting dirtied on initialization of containers and their processes, which ends up never read afterwards.
I always set up swap, because sacrificing some disk space in potential exchange of free RAM, which is orders of magnitudes more expensive, is a nice prospect.
So, the typical saving is tiny, and the cost in unpredictable performance is quite bad.
If you really do have an issue with “lost” dirty memory, your time is best spent addressing that directly.
I get the hibernation argument, but not the arguments implying swap is always better.
Actively using 60GB RAM and moving 4GB of unused pages to swap (60+4), is somehow faster than actively using 60GB RAM and keeping unused pages in the remaining 4GB RAM (64+0)?
EDIT: If you prefer more round numbers, feel free to replace them with "32GB RAM + 32GB swap" and "64GB RAM + no swap" respectively.
Say you have 64GB of RAM, of which 4GB are dirty pages that are never, or at least very rarely, accessed. With 64GB RAM + 4GB swap, you filled up your swap with them and have 64GB RAM left to use actively. With 64GB RAM + 0GB swap, you only have 60GB RAM left to use actively.
Use the 32+32 numbers if you're more comfortable with those round numbers.
If I have a system running comfortably with 32GB RAM + 32GB swap (no OOM, no swap thrashing), and I upgrade to 64GB RAM + 0 swap, what actual negative effects would I be getting for the lack of swap?
That's my question, to know if swap has any benefits other than being additional slow RAM.
We use swap because we have plenty of disk space, but (comparably) very little DRAM.
The same goes for another level on the hierarchy: If you could choose between 1GB of DRAM vs. 1GB of SRAM (which your CPU cache is), you’d definitely choose the SRAM. But you’d be paying out of your nose both with money and area, it’s not economical at all. My CPU has 96MB of cache, and that’s considered massive.
What does the OS do differently with swap vs RAM? What can I do with swap that I cannot do with RAM? Things like that.
If it's killing your email editor then your email editor is bloated or you just need more RAM - or swap.
In consequence, I always give swap. Even on the off-chance it ends up unused, disk space is orders of magnitude cheaper than RAM, so I don't mind sacrificing it for potential gains.
Not a big deal. Being efficient isn't really all it is cracked up to be. Sometimes having a big server that sits mostly idle is a good trade off for what you want to accomplish.