Re: [PATCH v2] vl/s390: fixup ram sizes for compat machines

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 01.04.20 12:13, Cornelia Huck wrote:
> On Wed,  1 Apr 2020 04:50:14 -0400
> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> 
>> Older QEMU versions did fixup the ram size to match what can be reported
>> via sclp. We need to mimic this behaviour for machine types 4.2 and
>> older to not fail on inbound migration for memory sizes that do not fit.
>> Old machines with proper aligned memory sizes are not affected.
>>
>> Alignment table:
>>  VM size (<=) | Alignment
>> --------------------------
>>       1020M   |     1M
>>       2040M   |     2M
>>       4080M   |     4M
>>       8160M   |     8M
>>      16320M   |    16M
>>      32640M   |    32M
>>      65280M   |    64M
>>     130560M   |   128M
>>     261120M   |   256M
>>     522240M   |   512M
>>    1044480M   |     1G
>>    2088960M   |     2G
>>    4177920M   |     4G
>>    8355840M   |     8G
>>
>> Suggested action is to replace unaligned -m value with a suitable
> 
> "to replace any unaligned -m value" ?
> 
>> aligned one or to use a machine version >= 5.0 as future versions might
>> remove the compatibility handling.
> 
> I'm confused by the second part of the sentence. Warning about possible
> future removal of the compat stuff is fine, but I don't understand the
> suggestion to use a machine type >= 5.0. If I create a new machine that
> does not need be migrated to an old QEMU, using the latest machine type
> always seems like the best idea, right? And for a migration target it's
> not like we can choose the version freely anyway.


My point was that - when you redefine your guest, which is disruptive anyway
you could also change the machine version to 5.0 and keep the strange memory
size.