I’ve heard a lot of people say your swap should be 2x RAM… but do I really need 32GB of 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
It’s something that Linux users have been saying for 20 years and it’s outdated. It makes sense when maybe your computer came with less than a GB of RAM, but these days I usually configure a server with a small amount of swap (like a couple of GB), and I set swappiness to something very low like 5.
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 Hell, even that might be outdated nowadays.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.
Even if you don’t run into RAM exhaustion, it is always good to have some swap space, as it can be used to move less used pages to swap, and frees up RAM for more filesystem cache.
I always keep a 2GB swap partition.
Personally I don’t think swap partitions are particularly useful any more
This is just wrong. Having swap increases the performance of your applications as it frees up RAM by swapping cold pages out of memory and use that space for caching, which increases hit rates. And this performance increase is both for low and high used memory rates.
So once it gets pushed out of RAM, you read it from disk instead of from disk? I’m not sure that that’s a benefit. If you’re using SSDs, they are fast and don’t have seek times, so I don’t think that having it in swap is any faster than just from disk. Maybe a little overhead for opening the file.
Assuming that you aren’t truly exhausting your RAM, anyway, such that programs start crashing due to being unable to allocate. Or that the data on disk is compressed, for example.
the swap space works as another level of memory hierarchy, the kernel swap pages out before all RAM is used in order to make room for pages that are more likely to be requested. It is very much a benefit, especially when using SSDs.
so I don’t think that having it in swap is any faster than just from disk.
That is still is faster, because even though they have the same physical access times, the data stored in swap space is already mapped to memory pages. By not using swap you are just more likely to face lower hit rates for low memory usage and thrashing for high memory usage. The slowness of the disk won’t affect your overall performance as you’ll get higher cache hit rates.
Right now for example, roughly half of my RAM is being used for caching and all of my swap is used. If I didn’t have swap, most of that space used for caching would instead be used for those cold memory pages.
I have a swap partition in my current system (64GB), I’ve had one on my previous system (which was 11 years old, with 16 GB) - I have seen my system¹ swap at most 5 times, and every time it was software misbehaving so badly that it made the system unusable.
I know this is anecdotal evidence - but my experience is that it’s getting less and less relevant for most desktop systems.
Edit: ¹my old system, the new one has not swapped at all in the past year.
@frustbox @sam I mostly agree, you should always aim to only use ram and not swap with your system. That beeing said you can have swap usage in any kind of system and even if you have terabytes of ram there is still a valid point for having some swap because that’s still better than a kernel panic. Also in desktop computers you can get 16-32GB RAm full while gaming and multitasking some stuff along.
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.
Hibernate and suspend are different. I configure my laptop to suspend for 3 hours before hibernating. That means I can close the lid for lunch or a commute and instantly resume, but if I leave my laptop in my bag over a long weekend, the battery isn’t drained. Does it save much battery? Dunno. A few % over a few days maybe.
