Re: [Qemu-ppc] [REBASE PATCH v5 1/2] machine: add default_ram_size to machine class

[Thomas Huth]

On Thu, 30 Apr 2015 11:18:05 +0200
Alexander Graf <address@hidden> wrote:

> 
> 
> On 30.04.15 06:41, Nikunj A Dadhania wrote:
> > 
> > Hi Paolo,
> > 
> > Paolo Bonzini <address@hidden> writes:
> >> On 29/04/2015 11:06, Nikunj A Dadhania wrote:
> >>>> so David can push both patches.
> >>>>
> >>>> But isn't 1G a bit too much?  At least on x86 you can easily boot with 
> >>>> 512M.
> >>>
> >>> I understood this number as not the _minimum memory_ to boot the
> >>> VM. And this will only come in picture when the user has not specified
> >>> any memory.
> >>
> >> This in turn will basically only happen for QEMU developers.  So keeping
> >> the default on the low side would make sense.
> >>
> >> On my (4G memory) laptop I might not even be able to boot a PPC64 VM
> >> with 1G and TCG, but I can do that nicely with 256M.
> > 
> > That will be fine with me as well, i.e. 256M
> > 
> > David/Alex, Do you have comments on this before we change it?
> 
> I've seen RAM size combinations that seemed to work ok, but then failed
> during grub2 execution for example. Please verify with all reasonably
> realistically executed distributions that 256MB is enough.

Since this default value will likely be there for the next couple of
years, it's maybe better to use a slightly higher value than one that
is too low - the amount of RAM that a guest requires likely rather
increases in the next years instead of going down again. So I think
using 512 MB instead is maybe a good compromise?

 Thomas