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ಠ_ಠ

SWAP RAM is useful for hibernation mode and fall back ram incase you have low memory.

I basically never used swap until I used some script that was supposed to de-duplicate text messages from SMS backups.

Turns out feeding it a 100,000 message archive spanning back 15 years will somehow eat up ~80GB of RAM. I doubt it should, I guess it probably just wasn’t optimized for such a large amount.

So I made a 64GB swap file and it completed fine.

Swap is there an emergency relief for when a runaway process starts to eat all the resources. The system gets slow the user says hey what’s that? They look and see oh wow this one process is really eating a lot of resources that’s bad, can I kill it or do I need to gracefully try to shut it down. Swap buys you time when it could matter. When you don’t have swap OOM killer takes out whatever it wants and for a desktop user that may not be that big of a deal but for a server the database is likely the first target that is taken out.

I used to be this guy. We have huge amount of memory in our storage server. Why would we need swap? Well, once the system started killing programs I read up on swap and how the system handles its caches, especially ZFS ARC.

Short version is that while the system can evict its caches syncronously, it can only async notify ZFS that it should also shrink its caches, but the out-of-memory killer will start killing before ZFS and its kernel counterpart can start to free up memory.

A tiny bit of swap completely solved this, since swapping is sync for the kernel and the OOM killer will wait for it.

ZFS chuckles darkly in the corner

No

It turns out the computer mostly freezes once you go past 200% RAM used.

“I’m not a friggin bear, I don’t hibernate!”

There are good use cases for swap. I work with very performance sensitive memory hogging applications that tend to process in bursts as incoming batched data arrives. We also have a lot of required background “security” applications.

Having the idle applications move out to swap so that a significant amount of free RAM to allow for the active, real-time applications to expand into is a major boon. RAM is expensive now, so it’s become even more critical to not waste it.

But even in self-hosting at home I take advantage of it since I have a limited number of servers with limited RAM and a bunch of applications and/or docker containers running, many of which don’t need to be active at all times, but if they were all active, would have trouble with the limited RAM. Swap allows for inactive applications to free up RAM for the active ones and leave enough available at all times to allow an application to quickly spin up new jobs.

Anyway, sure, for a simple desktop computer without a bunch of junk background applications running for “security” or whatever, and an overabundance of RAM installed, it’s probably not useful. But for high performance, memory hungry applications with lots of background stuff running, it can be a big help.

That said, there are use cases where the opposite is useful and using a RAM drive is better than writing to disk for cache and temporary logs when you have enough RAM. My opnsense router for instance uses a RAM drive to store cache and logs (logs are mirrored to the NAS for long term storage, so just the local copy is lost on reboot). That system has enough RAM and I’d rather reduce disk wear, and I don’t plan to add too many other applications to that server that it would run low.

Everyone defending swap like crazy in the comments… so let me give a counter argument specifically for desktop:

Many years ago I stopped using swap on all my computers (I exclusively use linux) and the reason is: every time anything regarding interactivity went to swap, my system would freeze and literally become unusable for a really long time until I killed something. Since I got tired if that behaviour I decided I prefer for random shit to die but my computer still be usable.

It wasn’t very often, but I don’t get OOM killer often either (as in I don’t remember the last time it happened and I use linux every day for both work and fun), and the freezing situation was way more annoying, to the point I sometimes ended up cold switching off the computer. I’m surprised on how many people run out of memory constantly. I guess you all are just using linux for servers and have crazy processing of infinite data…

All I know is that I had 16GB RAM and 4GB swap and I used to get crashes sometimes.

Set that fucker to 32GB out of spite, now no crashes. No idea why that helped. But I guess I do have like 15 tabs open on the regular (web dev)

The trick is to first create a RAM disk. Then put the swap file on there and it’s about as fast as RAM. Then, with the new memory you have created, make another RAM disk. Yep, then make more swap space on there.

I have solved both the memory and SSD availability issues with this infinite RAM and disk space trick.

I dislike swap solely because it gets used and when I accidentally open the same file twice then I regularly encounter problems with swap files when opening the file again later.

Definitely configure swap, but I don’t think there is much benefit of a swap partition over a swap file these days and swap files are trivial to configure.

People still use swap partitions instead of swap files?