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Re: [libvirt] [PATCH] docs: correct setmem text plus expand setmaxmem text



2011/1/19 Eric Blake <eblake redhat com>:
> On 01/18/2011 05:28 PM, Justin Clift wrote:
>> This completes the man page updates required for BZ # 622534:

>> +
>> +Some hypervisors require a larger granularity than kilobytes, and requests
>> +that are not an even multiple will either be rounded down or rejected.  For
>> +example, vSphere/ESX rejects the parameter unless the kB argument is evenly
>> +divisible by 1024 (that is, the kB argument happens to represent megabytes).
>> +
>> +Note, this command only works on active guest domains.  To change the memory
>> +allocation for an inactive guest domain, use the virsh B<edit> command to
>> +update the XML <memory> element.
>
> I guess this means some experimentation is in order to validate these
> claims.
>

Actually the ESX driver is a bit inconsistent in that regard. Most
times the code will just divide by 1024 when libvirt uses kilobytes
but ESX needs megabytes. It even ignores the case when this results in
0 megabytes.

The VMX handling code is stricter and rejects values that are not even
dividable by 1024, or by 4096 in case of <memory> or by 64 in case of
<video vram=...>. So this only affects virsh define and virsh dumpxml,
the only two places where the ESX driver uses the VMX handling code.

I wonder in which direction to go in order to unify this: being more
strict and do "value % 1024 == 0" checks all over the place, or being
less strict and just divide by 1024.

Matthias


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