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

[David Hildenbrand <david@redhat.com>]

> Am 10.07.2020 um 17:43 schrieb Heiko Carstens <hca@linux.ibm.com>:
> 
> 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
> guest.
> --------
> 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.
> 

Ah, yes. See the kernel patch, I take the max of both values (SCLP, diag260(0xc)) values.

Anyhow, what would be your recommendation?

Thanks!