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

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Date:   Wed, 01 Feb 2017 15:49:23 -0200
From:   Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        Paul Clarke <pc@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] powerpc/pseries: Dynamically increase RMA size

Hello,

Am Mittwoch, 1. Februar 2017, 16:37:58 BRST schrieb Michael Ellerman:
> Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com> writes:
> > Paul Clarke [pc@...ibm.com] wrote:
> > ---
> > 
> > From f9e9e8460206bc3fa7eaa741b9a2bde22870b9e0 Mon Sep 17 00:00:00 2001
> 
> 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 
obvious:

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

LoPAPR says that "The Initial size of the RMA is set to the greater of the 
values indicated by bytes 24-27 [min RMA] or 32 [min RMA percentage of total 
RAM] of option vector number 2 “Open Firmware” or minimum RMA size supported 
by the platform and capped by the maximum memory defined for the partition and 
the maximum size of the RMA supported by the platform. The respective selected 
values are reported in the length of the first memory property."

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

-- 
Thiago Jung Bauermann
IBM Linux Technology Center