[systemd-devel] systemd hibernator generator does not function on default Fedora install

[Zbigniew Jędrzejewski-Szmek]

On Thu, Apr 21, 2016 at 12:00:55PM -0600, Chris Murphy wrote:
> On Wed, Apr 20, 2016 at 3:14 AM, Lennart Poettering
> <lennart at poettering.net> wrote:
> > On Tue, 19.04.16 22:47, Chris Murphy (lists at colorremedies.com) wrote:
> >
> >> In some ancient bug or lkml I'd read a kernel maintainer say that the
> >> hibernation image size isn't fixed, and might be less than RAM size
> >> but could be a little more than RAM size, especially if some swap is
> >> being used. So what should swap partition size be to support
> >> hibernation? 1x RAM? 1.5x? 2x? Other?
> >
> > Here's the heuristics code logind uses to check whether hibernation
> > shall be considered available or not:
> >
> > https://github.com/systemd/systemd/blob/master/src/shared/sleep-config.c#L229
> >
> > i.e. it checks that the RAM size is smaller than 0.98 times the
> > currently unused swap space.
> 
> Default Fedora 24 installation, 'free' shows
> 
> Mem:  2048524
> Swap: 2098172

Just to clear up a misconception:

The check in enough_memory_for_hibernation() uses Active(anon), not
the total RAM size.  The line shown by free as "Mem" includes buffers
which are not included in Active(anon). The relevant field is
in the "+/- buffers" line. This is improved in the version of free
in F24, which does away with the "+/-" buffers line, and the
"Mem used" value is more meaningful.

> Mem is 0.976 times unused swap, on a clean boot where no swap at all
> is being used. If as little as 8MiB swap were used, sounds like
> hibernation would fail?
No, in the normal case it wouldn't.

Zbyszek