RE: [Xen-devel] How to request contiguous memory for a domu

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

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On Thu, 2011-07-21 at 09:57 +0100, Fan, Huaxiang wrote:
> Hi Ian,
> 
> Thanks for your quick reply.
> 
> We are running cpu/memory intensive application/services on a domu, we
> are worry about non-contiguous memory allocation might affect the
> performance. 
> 
> We are migrating the application/services from a single CPU socket (4
> cores, i.e. 8 ht cores) hardware platform to a dual CPU socket (8
> cores, i.e., 16 ht cores) hardware platform. And we saw performance
> degradation. As you know each physical and a half memory constitute a
> node. We also worry about the domu memory allocation across nodes
> boundary.

Does turning on Xen's NUMA support help at all? And then possibly
pinning each guests VCPUs to a particular physical node. IIRC xl has a
cpupool command which sets up a cpupool per node which might make this a
bit easier. I must admit though that I'm not too familiar with Xen NUMA
capabilities, hopefully someone else on the list can advise further.

Ian.

> 
> Thanks,
> Huaxiang
> 
> -----Original Message-----
> From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxx] 
> Sent: Thursday, July 21, 2011 4:45 PM
> To: Fan, Huaxiang
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] How to request contiguous memory for a domu
> 
> On Thu, 2011-07-21 at 09:28 +0100, Fan, Huaxiang wrote:
> > Hi gurus,
> > 
> >  
> > 
> > I used xen 3.4.2. I noticed that, every time I reboot my box, the dom0
> > occupy all available physical memory (except those used by xen
> > hypervisor), then /etc/init.d/xendomains try to boot domu specified
> > in /etc/xen/auto, then dom0 balloon out to free a portion of memory
> > (of course the resulting memory should be above dom0_min_mem) to meet
> > the memory requirement of incoming domu.
> > 
> >  
> > 
> > My question is, is there a guarantee that the domu get contiguous
> > physical memory?
> 
> No
> 
> >  Or how can I guarantee that?
> 
> A guest can try to exchange memory for contiguous memory using
> XENMEM_exchange but there are limits on how bug a single contiguous
> region can be requested that way (I think it's around order 9 or so).
> 
> Why do you want domU memory to be contiguous? There is no general
> requirement on dom0 or domU for this to be the case and the p2m/m2p
> mechanisms exist to allow non-contiguous machine memory. In general
> guests only need to arrange for contiguous memory for specific DMA
> buffers to specific physical devices which require it.
> 
> Please explain what you are actually trying to achieve so we can best
> advise you.
> 
> > (My memory capacity is big enough for meeting all domus and dom0
> > memory requirements.)
> > 
> >  
> > 
> > What about xen 4.1.0?
> > 
> >  
> > 
> > Thanks in advance.
> > 
> > HUAXIANG FAN
> > Software Engineer II
> > 
> > WEBSENSE NETWORK SECURITY TECHNOLOGY R&D (BEIJING) CO. LTD.
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