34 lines
1.9 KiB
Markdown
34 lines
1.9 KiB
Markdown
|
tags: linux
|
|||
|
|
date: 2020-01-25
|
|||
|
|
certainty: likely
|
|||
|
|
status: initial
|
|||
|
|
title: Preventing out-of-memory (OOM) errors on Linux
|
|||
|
|
|
|||
|
|
# Preventing out-of-memory (OOM) errors on Linux
|
|||
|
|
|
|||
|
|
I’ve been running out of memory more and more often lately. I don’t use any swap space because I am of the opinion that 16GB of memory should be sufficient for most daily and professional tasks. Which is generally true, however sometimes I have a runaway filling my memory. Emacs is very good at doing this for example, prone to filling your RAM when you open json files with very long lines.
|
|||
|
|
|
|||
|
|
In theory, the kernel OOM killer should come in and save the day, but the Linux OOM killer is notorious for being extremely … conservative. It will try to free every internal structure it can before even thinking about touching any userspace processes. At that point, the desktop usually stopped responding minutes ago.
|
|||
|
|
|
|||
|
|
Luckily the kernel provides memory statistics for the whole system, as well as single process, and the [`earlyoom`](https://github.com/rfjakob/earlyoom) tool uses those to keep memory usage under a certain limit. It will start killing processes, “heaviest” first, until the given upper memory limit is satisfied again.
|
|||
|
|
|
|||
|
|
On NixOS, I set:
|
|||
|
|
|
|||
|
|
```nix
|
|||
|
|
{
|
|||
|
|
services.earlyoom = {
|
|||
|
|
enable = true;
|
|||
|
|
freeMemThreshold = 5; # <%5 free
|
|||
|
|
};
|
|||
|
|
}
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
and after activation, this simple test shows whether the daemon is working:
|
|||
|
|
|
|||
|
|
```shell
|
|||
|
|
$ tail /dev/zero
|
|||
|
|
fish: “tail /dev/zero” terminated by signal SIGTERM (Polite quit request)
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
`tail /dev/zero` searches for the last line of the file `/dev/zero`, and since it cannot know that there is no next line and no end to the stream of `\0` this file produces, it will fill the RAM as quickly as physically possible. Before it can fill it completely, `earlyoom` recognizes that the limit was breached, singles out the `tail` command as the process using the most amount of memory, and sends it a `SIGTERM`.
|