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This is dangerous advice. At least on Ubuntu 16.04 with stock kernel running due to memory pressure into swap kills the systems. Basically everything times out

by nisa 9y ago

This is dangerous advice. At least on Ubuntu 16.04 with stock kernel running due to memory pressure into swap kills the systems. Basically everything times out and you can only hard-reboot. Without swap you have an OOM at least something you can recover from. If you need swap just add a little like 1-4gb - because if you have spinning disks 64gb swap won't help you at all because every request to swap is magnitudes more slower. Might be different with NVMe but it's still noticable.

ausjke 9y ago
indeed on ubuntu 16.04 64bit, when my chrome has 20+ tabs, some new tab could trigger a memory thrashing, that uses up all the memory and eats up a few GB disk, cpu load jumps up to 10x, the computer basically becomes unusable. i would rather a OOM kill the chrome process in this case, it wastes less time on me, a re-open of chrome will keep all the histories anyways. also on embedded system where the RAM is fairly limited, and no hard drive attached, and its storage is measured by MB instead of GB, you simply can not have the swap partition. I want to run the system without swap actually.
- warrenm 9y ago
  >when my chrome has 20+ tabs That's not a swap problem, that's a Chrome problem.
  - AstralStorm 9y ago
    It is a swap problem. Swap is supposed to make things work and not stop. I suppose this is actually a problem of Linux optimistic malloc policy.
tfha 9y ago
Not just ubuntu. We tell our engineers to remove their swap partitions because sometimes the test suite will consume all remaining memory and push into swap. If that happens, pretty much the only thing you can do is a hard poweroff. If you're fast, you can Ctrl+C and only lose a minute or two, but often you're just completely stuck. Much better to OOM and have the test suite killed early.
- Matt3o12_ 9y ago
  Wouldn’t it make much more sense to limit the maximum amount of memory available to something like (system memory-500MB) using CGroups? I know configuring CGroups can be difficult because there is no command line script but it might be worth it if it’s such a common problem with your test suits. An easy way to configure CGroups would be to use docker but that adds a lot of overhead in management (not in performance - but you need to have every dev install docker and test the suit using docker). I use swap quite a lot, though, I’m not sure what my system moves to swap though. A large portion seems to be inactive google chrome tabs (whenever I open an inactive tab, chrome freezes for a second and I suddenly use ~70MB less swap.
- cat199 9y ago
  > If that happens, pretty much the only thing you can do is a hard poweroff. Sounds like a non-swap system/kernel tuning issue - you should still be able to slowly switch to a virtual console or ssh in, etc, and kill the test suite.. Also, most linux distros run without any real usage of user/group resource limiting - setting up these appropriately is useful to limit the overall impact of runaway jobs
- cosarara97 9y ago
  Can ulimit help here?
  - AstralStorm 9y ago
    Ulimit is per process, it won't do. vm.overcommit_memory=2 with some setting of vm.overcommit_ratio or bytes will help though. I'd say overcommit heuristics break applications and cause them to eat too much memory since they don't know when to stop. The only trouble is KVM which for some reason takes double of process space allocated to the VM for no good reason and perhaps memory intensive Java. You need to tune the latter anyway.
warrenm 9y ago
Sorry, but this is just patently not true. See this list of many reasons why you're incorrect - https://news.ycombinator.com/item?id=15952447 https://news.ycombinator.com/item?id=15952447
- hyperpape 9y ago
  Thanks for the list of resources--I've been struggling to find good information about whether to use swap. A friendly suggestion: you obviously care a lot about this, and want to bring people around to your point of view. I think you'd be more effective at that, if you wrote this up as a blog post, or a github gist. Cite the relevant information from those links (or leave some of them as further reading). As it stands, there are 16 links, and I'm anticipating slogging through them, with no idea what I'm getting out of it.
  - jacquesm 9y ago
    > with no idea what I'm getting out of it. Not a whole lot. I've looked at them and they are for the most part outdated, do not make the case for 'some swap' or are simply fluff to make the list look more impressive.
    - warrenm 9y ago
      Half of them are older, half are new/current In short, unless you really know you don't need it, you should be running it

by nisa 9y ago

ausjke 9y ago

indeed on ubuntu 16.04 64bit, when my chrome has 20+ tabs, some new tab could trigger a memory thrashing, that uses up all the memory and eats up a few GB disk, cpu load jumps up to 10x, the computer basically becomes unusable. i would rather a OOM kill the chrome process in this case, it wastes less time on me, a re-open of chrome will keep all the histories anyways. also on embedded system where the RAM is fairly limited, and no hard drive attached, and its storage is measured by MB instead of GB, you simply can not have the swap partition. I want to run the system without swap actually.

warrenm 9y ago
>when my chrome has 20+ tabs That's not a swap problem, that's a Chrome problem.
- AstralStorm 9y ago
  It is a swap problem. Swap is supposed to make things work and not stop. I suppose this is actually a problem of Linux optimistic malloc policy.

tfha 9y ago

Not just ubuntu. We tell our engineers to remove their swap partitions because sometimes the test suite will consume all remaining memory and push into swap. If that happens, pretty much the only thing you can do is a hard poweroff. If you're fast, you can Ctrl+C and only lose a minute or two, but often you're just completely stuck. Much better to OOM and have the test suite killed early.

Matt3o12_ 9y ago
Wouldn’t it make much more sense to limit the maximum amount of memory available to something like (system memory-500MB) using CGroups? I know configuring CGroups can be difficult because there is no command line script but it might be worth it if it’s such a common problem with your test suits. An easy way to configure CGroups would be to use docker but that adds a lot of overhead in management (not in performance - but you need to have every dev install docker and test the suit using docker). I use swap quite a lot, though, I’m not sure what my system moves to swap though. A large portion seems to be inactive google chrome tabs (whenever I open an inactive tab, chrome freezes for a second and I suddenly use ~70MB less swap.
cat199 9y ago
> If that happens, pretty much the only thing you can do is a hard poweroff. Sounds like a non-swap system/kernel tuning issue - you should still be able to slowly switch to a virtual console or ssh in, etc, and kill the test suite.. Also, most linux distros run without any real usage of user/group resource limiting - setting up these appropriately is useful to limit the overall impact of runaway jobs
cosarara97 9y ago
Can ulimit help here?
- AstralStorm 9y ago
  Ulimit is per process, it won't do. vm.overcommit_memory=2 with some setting of vm.overcommit_ratio or bytes will help though. I'd say overcommit heuristics break applications and cause them to eat too much memory since they don't know when to stop. The only trouble is KVM which for some reason takes double of process space allocated to the VM for no good reason and perhaps memory intensive Java. You need to tune the latter anyway.

warrenm 9y ago

Sorry, but this is just patently not true. See this list of many reasons why you're incorrect - https://news.ycombinator.com/item?id=15952447 https://news.ycombinator.com/item?id=15952447

hyperpape 9y ago
Thanks for the list of resources--I've been struggling to find good information about whether to use swap. A friendly suggestion: you obviously care a lot about this, and want to bring people around to your point of view. I think you'd be more effective at that, if you wrote this up as a blog post, or a github gist. Cite the relevant information from those links (or leave some of them as further reading). As it stands, there are 16 links, and I'm anticipating slogging through them, with no idea what I'm getting out of it.
- jacquesm 9y ago
  > with no idea what I'm getting out of it. Not a whole lot. I've looked at them and they are for the most part outdated, do not make the case for 'some swap' or are simply fluff to make the list look more impressive.
  - warrenm 9y ago
    Half of them are older, half are new/current In short, unless you really know you don't need it, you should be running it