9 ms·

Nope. Those are not the only answers I am seeing. I’m still curious though. 2x was nice because nobody really questioned it. Now that we have there doesn’t seem

Nope. Those are not the only answers I am seeing. I’m still curious though. 2x was nice because nobody really questioned it. Now that we have there doesn’t seem to be one “answer”. This is a fun/interesting question that comes up every now and then here and elsewhere :-) I suspect someone smarter than me about system tuning will have a much smarter and nuanced answer than “just use 2x”

kgwxd 7mo ago
I thought the modern advice was you don't need it at all. No more spinning disks, so the there's no speed gain using the inner-most ring, and modern OSes manage memory in more advanced, and dynamic ways. That's what I choose to believe anyway, I don't need anymore hard choices when setting up Linux :)
- klempner 7mo ago
  The main downside to not having swap is that Linux may start discarding clean file backed pages under memory pressure, when if you had swap available it could go after anonymous pages that are actually cold. On a related note, your program code is very likely (mostly) clean file backed pages. Of course, in the modern era of SSDs this isn't as big of a problem, but in the late days of running serious systems with OS/programs on spinning rust I regularly saw full blown collapse this way, like processes getting stuck for tens of seconds as every process on the system was contending on a single disk pagefaulting as they execute code.
- anyfoo 7mo ago
  I don't think that's correct. Having swap still allows you to page out rarely-used pages from RAM, and letting that RAM be used for things that positively impact performance, like caching actually used filesystem objects. Pages that are backed by disk (e.g. files) don't need that, but anonymous memory that e.g. has only been touched once and then never even read afterwards should have a place to go as well. Also, without swap space you have to write out file backed pages, instead of including anonymous memory in that choice. For that reason, I always set up swap space. Nowadays, some systems also have compression in the virtual memory layer, i.e. rarely used pages get compressed in RAM to use up less space there, without necessarily being paged out (= written to swap). Note that I don't know much about modern virtual memory and how exactly compression interacts with paging out.
  - fluoridation 7mo ago
    Every time I've ran out of physical memory on Linux I've had to just reboot the machine, being unable to issue any kind of commands by input devices. I don't know what it is, but Linux just doesn't seem to be able to deal with that situation cleanly.
    - anyfoo 7mo ago
      The mentioned situation is not running out of memory, but being able to use memory more efficiently. Running out of memory is a hard problem, because in some ways we still assume that computers are turing machines with an infinite tape. (And in some ways, theoretically, we have to.) But it's not clear at all which memory to free up (by killing processes). If you are lucky, there's one giant with tens of GB of resident memory usage to kill to put your system back into a usable state, but that's not the only case.
      - fluoridation 7mo ago
        Windows doesn't do that, though. If a process starts thrashing the performance goes to shit, but you can still operate the machine to kill it manually. Linux though? Utterly impossible. Usually even the desktop environment dies and I'm left with a blinking cursor. What good is it to get marginally better performance under low memory pressure at the cost of having to reboot the machine under extremely high memory pressure?
        anyfoo 7mo ago
        In my experience the situations where you run into thrashing are rather rare nowadays. I personally wouldn't give up a good optimization for the rare worst case. (There's probably some knobs to turn as well, but I haven't had the need to figure that out.)
        fluoridation 7mo ago
        Try doing cargo build on a large Rust codebase with a matching number of CPU cores and GBs of RAM.
- vlovich123 7mo ago
  It’s still beneficial so that unused data pages are evicted in favor of more disk cache
man8alexd 7mo ago
I'm the OP. I got myself into collecting falsehoods people believe about Linux swap and OOM[1]. There is an entry about this 2x rule in this collection, with my answer on how to select swap size. My question on Retrocomputing.StackExchange is my attempt to add some historical background to this entry. [1]:https://alexeydemidov.com/2025/05/15/falsehoods-people-and-LLMs-believe-about-Linux-swap-and-OOM/ https://alexeydemidov.com/2025/05/15/falsehoods-people-and-L...

kgwxd 7mo ago

I thought the modern advice was you don't need it at all. No more spinning disks, so the there's no speed gain using the inner-most ring, and modern OSes manage memory in more advanced, and dynamic ways. That's what I choose to believe anyway, I don't need anymore hard choices when setting up Linux :)

klempner 7mo ago
The main downside to not having swap is that Linux may start discarding clean file backed pages under memory pressure, when if you had swap available it could go after anonymous pages that are actually cold. On a related note, your program code is very likely (mostly) clean file backed pages. Of course, in the modern era of SSDs this isn't as big of a problem, but in the late days of running serious systems with OS/programs on spinning rust I regularly saw full blown collapse this way, like processes getting stuck for tens of seconds as every process on the system was contending on a single disk pagefaulting as they execute code.
anyfoo 7mo ago
I don't think that's correct. Having swap still allows you to page out rarely-used pages from RAM, and letting that RAM be used for things that positively impact performance, like caching actually used filesystem objects. Pages that are backed by disk (e.g. files) don't need that, but anonymous memory that e.g. has only been touched once and then never even read afterwards should have a place to go as well. Also, without swap space you have to write out file backed pages, instead of including anonymous memory in that choice. For that reason, I always set up swap space. Nowadays, some systems also have compression in the virtual memory layer, i.e. rarely used pages get compressed in RAM to use up less space there, without necessarily being paged out (= written to swap). Note that I don't know much about modern virtual memory and how exactly compression interacts with paging out.
- fluoridation 7mo ago
  Every time I've ran out of physical memory on Linux I've had to just reboot the machine, being unable to issue any kind of commands by input devices. I don't know what it is, but Linux just doesn't seem to be able to deal with that situation cleanly.
  - anyfoo 7mo ago
    The mentioned situation is not running out of memory, but being able to use memory more efficiently. Running out of memory is a hard problem, because in some ways we still assume that computers are turing machines with an infinite tape. (And in some ways, theoretically, we have to.) But it's not clear at all which memory to free up (by killing processes). If you are lucky, there's one giant with tens of GB of resident memory usage to kill to put your system back into a usable state, but that's not the only case.
    - fluoridation 7mo ago
      Windows doesn't do that, though. If a process starts thrashing the performance goes to shit, but you can still operate the machine to kill it manually. Linux though? Utterly impossible. Usually even the desktop environment dies and I'm left with a blinking cursor. What good is it to get marginally better performance under low memory pressure at the cost of having to reboot the machine under extremely high memory pressure?
      - anyfoo 7mo ago
        In my experience the situations where you run into thrashing are rather rare nowadays. I personally wouldn't give up a good optimization for the rare worst case. (There's probably some knobs to turn as well, but I haven't had the need to figure that out.)
        fluoridation 7mo ago
        Try doing cargo build on a large Rust codebase with a matching number of CPU cores and GBs of RAM.
vlovich123 7mo ago
It’s still beneficial so that unused data pages are evicted in favor of more disk cache

man8alexd 7mo ago

I'm the OP. I got myself into collecting falsehoods people believe about Linux swap and OOM[1]. There is an entry about this 2x rule in this collection, with my answer on how to select swap size. My question on Retrocomputing.StackExchange is my attempt to add some historical background to this entry. [1]:https://alexeydemidov.com/2025/05/15/falsehoods-people-and-LLMs-believe-about-Linux-swap-and-OOM/ https://alexeydemidov.com/2025/05/15/falsehoods-people-and-L...