NUMA-aware VM placement in Xen

[Dario Faggioli <raistlin@linux.it>]

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Hi guys,

As some of you know I'm working on putting some kind of NUMA-aware
placement of the various VMs within Xen. This means I'm investigating
deeply how memory allocation works, which isn't an easy task for me (I
started completely from scratch), so forgive me if I say something
wrong! :-P

The status is I'm dealing for a while with a "design issue" I'd be very
glad to discuss with someone, as I'm not sure which path to go for...

To keep it short, what I need is a place --ideally during VM creation--
where I can check how much memory a VM wants against how much memory is
available in the various NUMA-nodes, and use this as the basis of my
decision. The question is, where is this place?

I traced memory related calls (e.g., for HVMs) from libxl__build_hvm to
xc_hvm_build_target_mem to setup_guest to xc_domain_populate_physmap and
alloc_domheap_pages. The last twos have been my target for a while, but
I'm not so sure they would be the right choice, mainly because both of
them are called for allocating _only_part_ of the VM's memory, i.e.,
some extents of it at each call (am I right?).

Basically, given alloc_domheap_pages uses d->node_affinity for deciding
from which node(s) to actually take memory from, I was planning to
either use the same mask or build a new one with similar purposes, the
problem being _where_ to populate it with the proper nodes.
I'm now looking at xc_domain_setmaxmem-->do_domctl(XEN_DOMCTL_max_mem),
although I think it's too early, and I'd end up guessing wrt a lot of
aspects... But considering xm/xend was doing the same even earlier (at
least I think)...

Sorry fro writing so much... Any help/ideas you feel comfortable with
sharing would be very appreciated! :-)

Thanks a lot and regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-------------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)



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