Re: how to let systemd hibernate start/stop the swap area?

[Lennart Poettering <lennart@xxxxxxxxxxxxxx>]

On Fr, 31.03.23 18:24, Michael Chapman (mike@xxxxxxxxxxxxxxxxx) wrote:

> On Fri, 31 Mar 2023, Barry wrote:
> [...]
> > If you want to run in ram only then you must turn off the kernel overcommit.
> > Have you done that? If not then you risk processes getting SEGV signals.
>
> Seriously. It's almost as if nobody here is actually reading anything of
> what I've written!
>
> EVERYTHING fits in RAM. The non-guest processes total perhaps a GB in
> total. The guest processes total maybe 200 GB in total. The server has
> more RAM than all of that.

I presume you are also running the OS itself from RAM then? i.e. your
rootfs is not backed by disk, but by some in-memory fs, or a loopback
on a memfd or so?

because otherwise you just remove the latencies from anonymous memory
but you amplify the latencies on file-backed memory. Which is overall
worse, not better.

> I know this works because I have literally done it on many, many
> hypervisors for over a decade.

I mean, you have a point: if you run on idle machines where hardware
is so massively oversized for the job you are doing, you can operate
really nicely without swap. No doubt. But that's kinda
wasteful. Resource-management through oversized hw is certainly a way to
solve problems, no doubt.

Lennart

--
Lennart Poettering, Berlin