RE: eliminating 166G limit (was Re: [Xen-devel] Problem with nr_nodeson large memory NUMA machine)

["Subrahmanian, Raj" <raj.subrahmanian@xxxxxxxxxx>]

Beth,
I am working on it.
I spoke to Keir about it at the Xen summit.
I hope to have a patch that will fix the issue and have the high-to-low memory 
copy working soon.

Thanks
Raj

>-----Original Message-----
>From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of beth kon
>Sent: Monday, December 03, 2007 2:50 PM
>Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: eliminating 166G limit (was Re: [Xen-devel]
>Problem with nr_nodeson large memory NUMA machine)
>
>Has there been any more thought on this subject? The
>discussion seems to have stalled, and we're hoping to find a
>way past this 166G limit...
>
>Jan Beulich wrote:
>
>>>>>Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> 27.11.07 10:21 >>>
>>>>>
>>>>>
>>>On 27/11/07 09:00, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>>>
>>>
>>>
>>>>>I don't get how your netback approach works. The pages we transfer
>>>>>do not originate from netback, so it has little control over them.
>>>>>And, even if it did, when we allocate pages for network receive we
>>>>>do not know which domain's packet will end up in each buffer.
>>>>>
>>>>>
>>>>Oh, right, I mixed up old_mfn and new_mfn in netbk_gop_frag().
>>>>Nevertheless netback could take care of this by doing the copying
>>>>there, as at that point i already knows the destination domain.
>>>>
>>>>
>>>You may not know constraints on that domain's max_mfn
>though. We could
>>>add an interface to Xen to interrogate that, but generally it's not
>>>something we probably want to expose outside of Xen and the
>guest itself.
>>>
>>>
>>
>>What constraints other than the guest's address size
>influence its max_mfn?
>>Of course, if there's anything beyond the address size, then having a
>>way to obtain the constraint explicitly would be desirable. But
>>otherwise (and as
>>fallback) using 37 bits (128G) seems quite reasonable.
>>
>>
>>
>>>>>Personally I think doing it in Xen is perfectly good enough for
>>>>>supporting this very out-of-date network receive mechanism.
>>>>>
>>>>>
>>>>I'm not just concerned about netback here. The interface
>exists, and
>>>>other users might show up and/or exist already. Whether it would be
>>>>acceptable for them to do allocation and copying is unknown. You'd
>>>>therefore either need a way to prevent future users of the transfer
>>>>mechanism, or set proper requirements on its use. I think that
>>>>placing extra requirements on the user of the interface is better
>>>>than introducing extra (possibly hard to reproduce/
>>>>recognize/debug) possibilities of failure.
>>>>
>>>>
>>>The interface is obsolete.
>>>
>>>
>>
>>Then it should be clearly indicated as such, e.g. by a mechanism
>>similar to
>>deprecated_irq_flag() in Linux 2.6.22. And as a result, its use in
>>netback should then probably be conditional upon an extra config
>>option, which could at once be used to provide a note to Xen that the
>>feature isn't being used so that the function could return
>-ENOSYS and the clipping could be avoided/reverted.
>>
>>Jan
>>
>>
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>>
>>
>
>
>--
>Elizabeth Kon (Beth)
>IBM Linux Technology Center
>Open Hypervisor Team
>email: eak@xxxxxxxxxx
>
>
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