Why is my server using all my Swap but I have RAM to spare?

Submitted ⁨⁨1⁩ ⁨week⁩ ago⁩ by ⁨mesamunefire@lemmy.world⁩ to ⁨selfhosted@lemmy.world⁩

https://lemmy.world/pictrs/image/ff619d4a-5d29-4866-b269-8bf60dd1c4cd.png

This is an old desktop I use for some small self hosting services. I never use all my RAM and I dont see any RAM spikes other than when I install/comile things which I havent done in months. I restarted the machine a couple of times, but the SWAP will evenually go right back up to 100%.

I have an Ubuntu server/yunohost setup and found: askubuntu.com/…/why-is-swap-being-used-even-thoug…

My cat /proc/sys/vm/swappiness value is indeed 60. Im not sure what would reduce the SWAP space usage.

Would changing this swappiness value help? Anyone come across this issue before?

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naomi@lemmy.amethyst.name ⁨1⁩ ⁨week⁩ ago
The naive approach of thinking of swap as “extra ram that is slow” and so “why is my system using swap when I have ram” is not really the best analogy. It’s better to think of ram as a place that holds memory pages, and disk as a place that holds file blocks/extents. Ram happens to be very fast and disk happens to be very slow, but conceptually programs access both memory pages and file blocks as they are running.

There is no reason that memory pages must live in ram, and no reason that file blocks must live on disk, especially in the modern world with virtual memory, and so sometimes it is more efficient for the kernel to say “hey, this memory page is never used and this file block is used a lot, so I’m going to put the memory page on disk and the file block in memory and everything will be faster.”

When a memory page is moved to disk, this is called swapping and the place it is stored on disk is swapspace. When a file block is stored in memory, this is called cache (or in some cases, buffers). So if you have plenty of ram free, it can still be beneficial for the kernel to move unused memory pages to swap to make space for cache. And once it is in swap, there’s no good reason to move it back until you need it, so even if space frees up in ram, the kernel won’t preemptively move it back into ram.

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- sugar_in_your_tea@sh.itjust.works ⁨1⁩ ⁨week⁩ ago
  It also takes a while to move stuff between RAM and disk, so it’ll park stuff in swap of it’s not used much to make room for burst RAM needs.
  
  Generally speaking, don’t worry about it as long as the system is responsive, but if things start sucking, consider closing stuff so the kernel can free it.
  
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- WhyJiffie@sh.itjust.works ⁨1⁩ ⁨week⁩ ago
  
  “hey, this memory page is never used and this file block is used a lot, so I’m going to put the memory page on disk and the file block in memory and everything will be faster.”
  
  except when not, like when I just copied a multi GB file, it was cached in RAM to be not read again for long, but at least half of my running programs are swapped out. Additionally if swap is o SSD, it has put totally unnecessary wear into it by doing this
  
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  - mlfh@lemmy.sdf.org ⁨1⁩ ⁨week⁩ ago
    That’s why you can adjust swappiness, or designate a different high-endurance storage device for it.
    
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Shimitar@downonthestreet.eu ⁨1⁩ ⁨week⁩ ago
1gb swap is way too small…

I usually setup swap to be 2x the total ram size. So, 32gb swap in your case.

Nothing wrong here, seems normal. With such little swap.

Actually Linux kernel works better with swap, the more the better. It will lalso perform better than zero swap. Counterintuitive indeed, but that’s how it works.

If you don’t want swap, use zram.

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- sugar_in_your_tea@sh.itjust.works ⁨1⁩ ⁨week⁩ ago
  32GB of swap is huge, I wouldn’t bother with that much unless you’re suspending to disk regularly. I personally just suspend to RAM and call it a day.
  
  On my laptop with 24GB RAM, I have about 20GB swap, which matches the system memory (rest is dedicated to my APU). On my desktop with 16GB RAM, I have 16GB swap, because that’s what my OS picked (I would otherwise go with 10GB). On both systems, I usually only have 2-3GB in swap anyway.
  
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- DasFaultier@sh.itjust.works ⁨1⁩ ⁨week⁩ ago
  +1 for zramswap, especially if you’re tight on RAM but have a few CPU cycles to spare.
  
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- N0x0n@lemmy.ml ⁨1⁩ ⁨week⁩ ago
  I though that the recommended swap partition was to double until 16 GB? So at 32GB of ram use 32GB of swap?
  
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  - GnuLinuxDude@lemmy.ml ⁨1⁩ ⁨week⁩ ago
    You should just maintain awareness of how much you’re using. I think 32gb ram + 32gb swap is ridiculous, frankly. Fedora by default sets zram up to 8gb, with no other swap space configured. Works very well that way.
    
    Personally I’d also probably not ever set up more than 16gb of swap space. If I’m somehow hitting that limit it’s because I actually just need to buy more RAM.
    
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- mesamunefire@lemmy.world ⁨1⁩ ⁨week⁩ ago
  Yeah I was thinking of adding swap as my other systems have lots more.
  
  This is just the default on yunohost.
  
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ianhclark510@lemmy.blahaj.zone ⁨1⁩ ⁨week⁩ ago
You’re not likely to get far with a 16x RAM -> swap ratio

Also all a full swap means is that your computer has determined that it has 976M of cold pages that were eligible to be swapped out

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irotsoma@lemmy.blahaj.zone ⁨1⁩ ⁨week⁩ ago
Note that often it’s more efficient to move infrequently accessed memory for background tasks to swap rather than having to move that out to swap when something requires the memory causing a delay in loading the application trying to get the RAM, especially on a system with lower total RAM. This is the typical behavior.

However, if you need background tasks to have more priority than foreground tasks, or it truly is a specific application that shouldn’t be using swap and should be quickly accessible at all times, or if you need the disk space, then you might benefit from reducing the swap usage. Otherwise, let it swap out and keep memory available.

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just_another_person@lemmy.world ⁨1⁩ ⁨week⁩ ago
What do you think it’s going to help? You sound like you’re absolutely sure there is something wrong here. You sure there’s something wrong?

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- mesamunefire@lemmy.world ⁨1⁩ ⁨week⁩ ago
  Might not be, it’s just strange.
  
  My other Linux machines use much less. And using Linux for as long as I have, swap space is usually reserved when there is a huge increase in ram usage.
  
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  - just_another_person@lemmy.world ⁨1⁩ ⁨week⁩ ago
    No, not a huge increase. It’s whatever is deemed to be most efficient at the time. You should get more familiar with how RAM is committed and used if you’re suspecting something. Perhaps in this case it’s all just committed cache memory and not contiguous tracts being reserved.
    
    Get the output of free -m
    
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InvertedParallax@lemm.ee ⁨1⁩ ⁨week⁩ ago
It pushes stuff when they’re really really cold, so for instance init services and libs that have basically never been touched since boot but still technically need to be in memory.

They might have been pushed out because the page cache thought it had something more interesting, or if you have VMs, because the system wanted to make some huge pages.

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possiblylinux127@lemmy.zip ⁨1⁩ ⁨week⁩ ago
I would turn swap off honestly. Chances are you aren’t going to have issues with 16GB.

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- joshcodes@programming.dev ⁨1⁩ ⁨week⁩ ago
  Counter point, set the ‘swappiness’ lower than the default 60. I’ve set mine to 30 and the system boots a lot faster. You could research and consider 10-20.
  
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  - possiblylinux127@lemmy.zip ⁨1⁩ ⁨week⁩ ago
    What are you using swap for? On Fedora installs the swap is just zram.
    
    The worst case without swap is that oom gets triggered. If 16GB gets eaten up chances are it is a single app.
    
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MTK@lemmy.world ⁨1⁩ ⁨week⁩ ago
Maybe he… Swaped them! 👍😎👌

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LodeMike@lemmy.today ⁨1⁩ ⁨week⁩ ago
No reason to remove something from swap which is already there. It does this for files too.

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RedWeasel@lemmy.world ⁨1⁩ ⁨week⁩ ago
Swap is used to defrag ram on linux. Could be related to that. In any case this is pretty normal. I have 43Gi available and it is used 700Mi of swap.

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drkt_@lemmy.dbzer0.com ⁨1⁩ ⁨week⁩ ago
Change swappiness to 10 and ensure that you don’t have anything dynamically adjusting it.

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neidu3@sh.itjust.works ⁨1⁩ ⁨week⁩ ago
Any way of having this study an existing database (or dump thereof) and build the graph?

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