[systemd-devel] how to let systemd hibernate start/stop the swap area?

[Michael Chapman]

On Mon, 3 Apr 2023, Lennart Poettering wrote:
> On Sa, 01.04.23 06:16, Michael Chapman (mike at very.puzzling.org) wrote:
> 
> > > Well, in larger environments the goal is typically to saturate all
> > > hosts, but not overload them. i.e. maximizing your ROI. No need to
> > > fall from one extreme into the other. Today's Linux can actually
> > > achieve something like this, if you use it properly. Swap is part of
> > > using it "properly".
> > >
> > > Oversized hw is typically a bad investment. In particular in today's
> > > cloud world where costs multiply with every node you have.
> >
> > If customers have paid for RAM, you don't turn around and given them swap
> > instead. That's just plain dishonest.
> 
> This is nonsense. Your VM images are typically backed by disk, no? You
> just amplify IO on that.

No, you don't... because _exactly the same_ IO is done. Once the swap is 
full, the existence of swap doesn't change what gets paged in or out on 
the host side, and it doesn't change which parts of guest RAM gets paged 
in or out. (And I really _don't want_ guest RAM to be paged in or out... 
we had sold it as RAM!)

> Anyway, you apparently think you know MM better than the fb folks who
> wrote the stuff. Good for you then! Since it doesn't look likely that
> anyone can convince you otherwise, let's end this dicussion here.

I find it very upsetting that you assume I just made all of this up. I did 
measurements. The results showed that swap made no difference to guest 
performance. If it made the guests perform better I would have kept it!

But yes, if you don't believe me I think it is best that we leave it at 
that. I honestly can't think of any other way to convince you.