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Debian 9.4, Linux 4.9

I sometimes compile something that hardly fits in the RAM, or a rouge process suddenly starts eating memory beyond what's available. When the process goes past the available RAM, Linux starts thrashing the disk even though I have zero swap enabled (no swap was an attempt to avoid this). I guess it starts discarding and reloading stuff like the mmapped parts of the binaries that are currently running?

At this point my X session quickly becomes unresponsive, and all I can do is wait dozens of minutes until the entire X session gets killed and I can log back in.

I tried to search around for solutions, but nothing seems to work. The OOM killer doesn't catch this process and with vm.overcommit_memory=2 I can't even log in with GDM and Gnome.

Is there a way to tell Linux not to swap at all? That way I would at least get a chance that the rouge process will be killed by a failed malloc, and even if not, at least I wouldn't need to wait while staring at an unresponsive machine.

Or any other hints how to manage this scenario?

attila lendvai
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2 Answers2

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I don't understand how people can recommend adding more RAM or more swap space. A misbehaving application can eat it all and reproduce the problem.

This kind of freezes are a serious architectural bug in the linux kernel. The only way to recover once the freezing happens is to force the OOM with a magic key (alt+sysrq+f). The kernel log will tell you later what was killed and why.

Several projects are trying to prevent this freezes from the userspace. See earlyOOM for example.

user1720077
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If you are compiling sources that require almost all the available RAM, if not more, probably the only performant solution is adding real RAM. Having said that, you may try adding a very large amount of swap (say 2x or 3x the RAM) and set /proc/sys/vm/swappiness to a low value, like 1 (note that with kernel 3.5+ setting it to 0 totally disables swap), so that swap is used only if effectively necessary. This should minimize thrashing.

Marco Pantaleoni
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