Re: [PATCH 2/2] powerpc/pseries: Dynamically increase RMA size

[Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>]

Hello,

Am Mittwoch, 1. Februar 2017, 16:37:58 BRST schrieb Michael Ellerman:
> Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> writes:
> > Paul Clarke [pc@us.ibm.com] wrote:
> > ---
> >=20
> > From f9e9e8460206bc3fa7eaa741b9a2bde22870b9e0 Mon Sep 17 00:00:00 2001
>=20
> I know it's been a while but I think it would still be good to get this
> in a shape that we can merge it.

Sorry if this has been tried and didn't work or if I'm missing something=20
obvious:

Instead of this method of trying a small RMA size and rebooting to try a=20
bigger size, could the "min RMA percentage of total RAM" field of the=20
ibm_architecture_vec be used?

LoPAPR says that "The Initial size of the RMA is set to the greater of the=
=20
values indicated by bytes 24-27 [min RMA] or 32 [min RMA percentage of tota=
l=20
RAM] of option vector number 2 =E2=80=9COpen Firmware=E2=80=9D or minimum R=
MA size supported=20
by the platform and capped by the maximum memory defined for the partition =
and=20
the maximum size of the RMA supported by the platform. The respective selec=
ted=20
values are reported in the length of the first memory property."

My understanding is that these patches are intended for big guests with man=
y=20
processors, but the RMA size isn't changed to 512MB outright because of=20
worries that it could affect smaller guests. Since guests with many process=
ors=20
tend to have more RAM as well, specifying a min RMA size of 256MB and a min=
=20
RMA percentage of, say, 10% or 20% could make the host automatically alloca=
te=20
an adequate RMA size in the first boot.

=2D-=20
Thiago Jung Bauermann
IBM Linux Technology Center