Re: [Xen-devel] [PATCH] Disallow setting maxmem to higher value than total physical memory size

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Wed, 2010-09-01 at 15:18 +0100, Michal Novotny wrote:

> Oh, ok. It's not limited to dom0 nevertheless I don't see anything to be 
> causing anything bad in domU. Of course, I can limit this to dom0 but 
> for domU you can be having e.g. this:
> 1)
> dom0: total memory = 8192
> domU: memory = 4096, maxmem = 8192 (xm mem-max domU 16384 fails)

It is useful, legal and valid to set e.g. maxmem = 12288 here, leaving
memory = 4096. Your patch prevents that.

> 2)
> and when you migrate to host B:
> dom0: total memory = 16384
> domU: memory = 4096, maxmem = 8192

If maxmem = 12288 then it would be possible to balloon this guest up to
12288 on this system. With your patch it is no longer possible. Note
that maxmem cannot change once the domU is booted so it needs to have
been = 12288 at the time the guest was created on Host A.

> 
> Or should I just ignore the possibility domU maxmem could be set to 
> higher value than host machine could provide and should I limit my check 
> to dom0 only?

Yes!

I haven't considered the applicability of this patch to dom0
particularly deeply but it is wrong to enforce this constraint on domUs.

Ian.


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel