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Re: [PATCH RFC 2/5] s390x: implement diag260

From: Heiko Carstens
Subject: Re: [PATCH RFC 2/5] s390x: implement diag260
Date: Fri, 10 Jul 2020 17:43:02 +0200

On Fri, Jul 10, 2020 at 05:24:07PM +0200, David Hildenbrand wrote:
> On 10.07.20 17:18, Heiko Carstens wrote:
> > On Fri, Jul 10, 2020 at 02:12:33PM +0200, David Hildenbrand wrote:
> >>> Note: Reading about diag260 subcode 0xc, we could modify Linux to query
> >>> the maximum possible pfn via diag260 0xc. Then, we maybe could avoid
> >>> indicating maxram size via SCLP, and keep diag260-unaware OSs keep
> >>> working as before. Thoughts?
> >>
> >> Implemented it, seems to work fine.
> > 
> > The returned value would not include standby/reserved memory within
> > z/VM. So this seems not to work.
> Which value exactly are you referencing? diag 0xc returns two values.
> One of them seems to do exactly what we need.

Maybe I'm missing something as usual, but to me this
Usage Notes:
2. If the RESERVED or STANDBY option was used on the DEFINE STORAGE
command to configure reserved or standby storage for a guest, the
values returned in Rx and Ry will be the current values, but these
values can change dynamically depending on the options specified and
any dynamic storage reconfiguration (DSR) changes initiated by the
reads like it is not doing what you want. That is: it does *not*
include standby memory and therefore will not return the highest
possible pfn.

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