[Libvir] [RFC] Check host's minimum memory.

[Atsushi SAKAI]

Hi, Dan

 I and Sunou investivate this issue.

  virsh setmem commands directry writes xenstore(memory/target) 
by using xenStoreDomainSetMemory()@xs_internal.c.
This data (memory/target) is read by PVdomain balloon driver directly.
As you know, xenstore just pass through the data between inter domain.
For this reason, virsh setmem must protect at xs_internal.c not on Xen-side

Anyway xm mem-set uses setMemoryTarget()@XendDomainInfo.py 
and write xenstore(memory/target).
This path can be protected by XenD fixes.

How should we do? 

Thanks
Atsushi SAKAI


Atsushi SAKAI <sakaia at jp.fujitsu.com> wrote:

> Hi, Dan
> 
> O.K.
> 
> I will asking Xen-devel with policy forcing patch.
> 
> Thanks
> Atsushi SAKAI
> 
> "Daniel P. Berrange" <berrange at redhat.com> wrote:
> 
> > On Wed, Mar 07, 2007 at 06:43:14AM -0500, Daniel Veillard wrote:
> > > On Tue, Mar 06, 2007 at 02:40:24PM +0900, Masayuki Sunou wrote:
> > > > Hi
> > > > 
> > > > The minimum value of the memory guarded with virsh setmem is 4096KB(4MB).
> > > > In general, when host's memory is set to 4MB, the host stops.
> > > > 
> > > > Therefore, I propose the patch to which host's minimum value of the memory
> > > > is guarded by 256MB.
> > > 
> > >   I have run guests in 64MB of memory, so 256 as an arbitrary limit sounds
> > > way too high to me. There is some places in libvirt code where 64 is the limit
> > > (e.g. xend_parse_sexp_desc() if ((cur_mem > 63) && (cur_mem != max_mem)) ...)
> > > so if we set a limit here too that should be homogenized (using a constant
> > > in internal.h preferably).
> > 
> > This still feels wrong to me - I'm don't like the idea of libvirt enforcing
> > policy decisions, particularly when they're compiled in. With the current
> > bloated Xen python stack we probably won't go below 64 MB, but we won't always
> > be managing Xen, nor will Xen forever be stuck with a python stack (i hope :-). 
> > I'd say that if possible XenD should be fixed to honour dom0_min_memory in all
> > cases, rather than just when ballooning down to start a guest.
> > 
> > Regards,
> > Dan.
> > -- 
> > |=- Red Hat, Engineering, Emerging Technologies, Boston.  +1 978 392 2496 -=|
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