I’ve heard a lot of people say your swap should be 2x RAM… but do I really need 32GB of swap?
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.
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.
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 don’t think swappiness has worked that way for a while now.
I’m one of those people.
I will leave you this: https://chrisdown.name/2018/01/02/in-defence-of-swap.html
This is a nice read from a kernel developer responsible for memory management.
@takeda
Thanks for sharing. Always good to learn more.
@sam @SJ_Zero @selfhosted
Hi there! Looks like you linked to a Lemmy community using an URL instead of its name, which doesn’t work well for people on different instances. Try fixing it like this: !selfhosted@lemmy.world
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.
@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.
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.
depends on what your apps are doing, a lot of the servers ive installed i seem to need to force to use more memory instead of some internal disk cache it already has. its adjustable and youll know when you need it.
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
