3 ms·

Both Canonical and Microsoft recommend enabling swap file for Ubuntu cloud images, even if you allocate plenty of RAM to the VM. Any thoughts on that?

man8alexd 9mo ago
https://chrisdown.name/2018/01/02/in-defence-of-swap.html https://chrisdown.name/2018/01/02/in-defence-of-swap.html
- AtlasBarfed 9mo ago
  I get we want a magical OS that reads minds and abstracts itself from users, but these days low mem situations are technical events for people trying to optimize resources use and balance uptime. So not being able to mark apps processes as kill me first and leave others like ssh bash up is a missing feature. Shouldn't the os have a bunch of auto hooks to invoke for machines under duress? Yes you might be able to do it in userspace but .. userspace will probably get unpredictability nuked in stress situations. The WMs should have a "freeze all apps desktop except this one shell window" mode. Didn't NeXT have that? Having some swap basically required has always seemed like a smell. A legacy from the 640k oops wasn't enough days. I can see emergency memory swap system as a feature, which it currently isn't...
  - man8alexd 9mo ago
    > So not being able to mark apps processes as kill me first and leave others like ssh bash up is a missing feature. systemd OOMScoreAdjust has existed for at least a decade. /proc/*/oom_adj since Linux kernel 2.6.11 - two decades. cgroups are also two decades old. SSH by default has OOMScoreAdjust=-1000 and is entirely protected from OOM.
IshKebab 9mo ago
Yeah because Linux's memory management is quite poor and running out of RAM without swap will often mean a hard reboot. Swap definitely helps a lot, even if it doesn't fully solve the problem. To be honest I don't know why it's such an issue on Linux. Mac and Windows don't have this issue at all. Windows presumably because it doesn't over-commit memory. I'm not sure why Mac is so much better than Linux at memory management. My eventual solution was to just buy a PC with a ton of RAM (128 GB). Haven't had any hard reboots due to OOM since then!
- direwolf20 9mo ago
  My experience is different. Running out of RAM without swap will cause the most memory–hungry process to die, whereupon systemd restarts it. Running out of RAM with swap causes thrashing and you can't serve any requests or ssh logins. Someone has to press the reset button then.
  - rustyhancock 9mo ago
    I suppose there are two common scenarios roughly. If I did something (like try and decompress an archive) and I run out of memory I want that process to be killed. If my system/config is simply not up to scratch and the normal services are causing thrashing that needs to be addressed directly and OOM kill isn't intended to help I don't think.
- NekkoDroid 9mo ago
  > To be honest I don't know why it's such an issue on Linux. Mac and Windows don't have this issue at all. Windows presumably because it doesn't over-commit memory To be fair, my Windows system grinds to a halt (not really, but it becomes very noticably less responsive in basically anything) when JetBrains is installing an update (mind you I only have SSDs with all JetBrains stuff being on an NVMe). I don't know what JetBrains is doing, but it consistently makes itself noticable when it is updating.
  - IshKebab 9mo ago
    I have had this happen in the past (not very often though), and another saving grave of Windows is you can press ctrl-alt-del, which somehow seems to pause the rest of the system activity, and then see a process list and choose which one to kill. Linux doesn't have anything like that. KDE seems to have a somewhat functional Ctrl-alt-del menu - I have been able to access it when the rest of the shell gets screwed up (not due to OOM). But inexplicably the only options it has are Sleep, Restart, Shutdown or Log out!! Where is the "emergency shell", or "process manager" or even "run a program"? Ridiculous. I think Linux GUIs often have this weird fetish with designing as if nothing will ever go wrong, which is clearly not how the real world works. Especially on Linux. I've genuinely heard people claim that most Linux users will never need to use a terminal for example.
secondcoming 9mo ago
would that mean swapping involves network calls?

man8alexd 9mo ago

https://chrisdown.name/2018/01/02/in-defence-of-swap.html https://chrisdown.name/2018/01/02/in-defence-of-swap.html

AtlasBarfed 9mo ago
I get we want a magical OS that reads minds and abstracts itself from users, but these days low mem situations are technical events for people trying to optimize resources use and balance uptime. So not being able to mark apps processes as kill me first and leave others like ssh bash up is a missing feature. Shouldn't the os have a bunch of auto hooks to invoke for machines under duress? Yes you might be able to do it in userspace but .. userspace will probably get unpredictability nuked in stress situations. The WMs should have a "freeze all apps desktop except this one shell window" mode. Didn't NeXT have that? Having some swap basically required has always seemed like a smell. A legacy from the 640k oops wasn't enough days. I can see emergency memory swap system as a feature, which it currently isn't...
- man8alexd 9mo ago
  > So not being able to mark apps processes as kill me first and leave others like ssh bash up is a missing feature. systemd OOMScoreAdjust has existed for at least a decade. /proc/*/oom_adj since Linux kernel 2.6.11 - two decades. cgroups are also two decades old. SSH by default has OOMScoreAdjust=-1000 and is entirely protected from OOM.

IshKebab 9mo ago

Yeah because Linux's memory management is quite poor and running out of RAM without swap will often mean a hard reboot. Swap definitely helps a lot, even if it doesn't fully solve the problem. To be honest I don't know why it's such an issue on Linux. Mac and Windows don't have this issue at all. Windows presumably because it doesn't over-commit memory. I'm not sure why Mac is so much better than Linux at memory management. My eventual solution was to just buy a PC with a ton of RAM (128 GB). Haven't had any hard reboots due to OOM since then!

direwolf20 9mo ago
My experience is different. Running out of RAM without swap will cause the most memory–hungry process to die, whereupon systemd restarts it. Running out of RAM with swap causes thrashing and you can't serve any requests or ssh logins. Someone has to press the reset button then.
- rustyhancock 9mo ago
  I suppose there are two common scenarios roughly. If I did something (like try and decompress an archive) and I run out of memory I want that process to be killed. If my system/config is simply not up to scratch and the normal services are causing thrashing that needs to be addressed directly and OOM kill isn't intended to help I don't think.
NekkoDroid 9mo ago
> To be honest I don't know why it's such an issue on Linux. Mac and Windows don't have this issue at all. Windows presumably because it doesn't over-commit memory To be fair, my Windows system grinds to a halt (not really, but it becomes very noticably less responsive in basically anything) when JetBrains is installing an update (mind you I only have SSDs with all JetBrains stuff being on an NVMe). I don't know what JetBrains is doing, but it consistently makes itself noticable when it is updating.
- IshKebab 9mo ago
  I have had this happen in the past (not very often though), and another saving grave of Windows is you can press ctrl-alt-del, which somehow seems to pause the rest of the system activity, and then see a process list and choose which one to kill. Linux doesn't have anything like that. KDE seems to have a somewhat functional Ctrl-alt-del menu - I have been able to access it when the rest of the shell gets screwed up (not due to OOM). But inexplicably the only options it has are Sleep, Restart, Shutdown or Log out!! Where is the "emergency shell", or "process manager" or even "run a program"? Ridiculous. I think Linux GUIs often have this weird fetish with designing as if nothing will ever go wrong, which is clearly not how the real world works. Especially on Linux. I've genuinely heard people claim that most Linux users will never need to use a terminal for example.

secondcoming 9mo ago

would that mean swapping involves network calls?