Comment on Help with understanding memory usage discrepancy

• eager_eagle@lemmy.world ⁨1⁩ ⁨day⁩ ago

  if my system touches SWAP at all, it’s run out of memory

  That’s a swap myth. Swap is not an emergency memory, it’s about creating a memory reclamation space on disk for anonymous pages (pages that are not file-backed) so that the OS can more efficiently use the main memory.

  The swapping algorithm does take into account the higher cost of putting pages in swap. Touching swap may just mean that a lot of system files are being cached, but that’s reclaimable space and it doesn’t mean the system is running out of memory.

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  • a_fancy_kiwi@lemmy.world ⁨22⁩ ⁨hours⁩ ago

    From what I can tell, my system isn’t currently using swap at all but it does have 8GB of available swap if needed.

    To make sure I’m following what you are saying, if I upgraded my system to 64GB and changed nothing else, and let’s assume ZFS didn’t trying caching more stuff, would there still be a potential for my system to use swap just because the system wanted to even if it wasn’t memory constrained?

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    • eager_eagle@lemmy.world ⁨21⁩ ⁨hours⁩ ago

      yes, the system will likely use some swap if available even when there’s plenty of free RAM left:

      The casual reader1 may think that with a sufficient amount of memory, swap is unnecessary but this brings us to the second reason. A significant number of the pages referenced by a process early in its life may only be used for initialisation and then never used again. It is better to swap out those pages and create more disk buffers than leave them resident and unused.

      Src: www.kernel.org/doc/gorman/…/understand014.html

      In my recently booted system with 32GB and half of that free (not even “available”), I can already see 10s of MB of swap used.

      As rule of thumb, it’s only a concern or indication that the system is/was starved of memory if a significant share of swap is in use. But even then, it might just be some cached pages hanging around because the kernel decided to keep instead of evicting them.

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      • a_fancy_kiwi@lemmy.world ⁨15⁩ ⁨hours⁩ ago

        TIL. Thanks for the information

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• EarMaster@lemmy.world ⁨1⁩ ⁨day⁩ ago

  If that’s the case you should look into your swappiness settings. You can set this to zero meaning the swap will only be used if you’re actually out of memory, but as others have noted that is maybe not a healthy decision…

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  • a_fancy_kiwi@lemmy.world ⁨22⁩ ⁨hours⁩ ago

    I’m currently not in a situation where swap is being used so I think my system is doing fine right now. I’m not against swap, I get it’s better to have it than not but my intention was to figure out how close is my system getting to using swap. If it went from not using swap at all to using it constantly, I’d probably want to upgrade my ram, right? If nothing else just to avoid system slow downs and unneeded wear on my SSD

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• victorz@lemmy.world ⁨1⁩ ⁨day⁩ ago

  It’s just that the system freezes for me when I used to run out of memory when I had only 32 GB of memory. Then I couldn’t do anything and had to hard reset the computer with its reset button. Then it would be nice to have a little bit of swap to kill some stuff before literally everything just stops working.

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  • B0rax@feddit.org ⁨1⁩ ⁨day⁩ ago

    Was that on Linux?

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    • victorz@lemmy.world ⁨1⁩ ⁨day⁩ ago

      Yeah, on multiple computers. Linux I feel will just happily hand out memory on loan like a bank rather than from what’s actually available. Then when it runs out, the next request for more memory will just freeze the system. ☠️

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