Re: [Qemu-devel] [PATCH 0/2][RFC] postcopy migration: Linux char device for postcopy

[Isaku Yamahata <yamahata@valinux.co.jp>]

One more question.
Does your architecture/implementation (in theory) allow KVM memory
features like swap, KSM, THP?


On Fri, Jan 13, 2012 at 11:03:23AM +0900, Isaku Yamahata wrote:
> Very interesting. We can cooperate for better (postcopy) live migration.
> The code doesn't seem available yet, I'm eager for it.
> 
> 
> On Fri, Jan 13, 2012 at 01:09:30AM +0000, Benoit Hudzia wrote:
> > Hi,
> > 
> > Sorry to jump to hijack the thread  like that , however i would like
> > to just to inform you  that we recently achieve a milestone out of the
> > research project I'm leading. We enhanced KVM in order to deliver
> > post copy live migration using RDMA at kernel level.
> > 
> > Few point on the architecture of the system :
> > 
> > * RDMA communication engine in kernel ( you can use soft iwarp or soft
> > ROCE if you don't have hardware acceleration, however we also support
> > standard RDMA enabled NIC) .
> 
> Do you mean infiniband subsystem?
> 
> 
> > * Naturally Page are transferred with Zerop copy protocol
> > * Leverage the async page fault system.
> > * Pre paging / faulting
> > * No context switch as everything is handled within kernel and using
> > the page fault system.
> > * Hybrid migration ( pre + post copy) available
> 
> Ah, I've been also planing this.
> After pre-copy phase, is the dirty bitmap sent?
> 
> So far I've thought naively that pre-copy phase would be finished by the
> number of iterations. On the other hand your choice is timeout of
> pre-copy phase. Do you have rationale? or it was just natural for you?
> 
> 
> > * Rely on an independent Kernel Module
> > * No modification to the KVM kernel Module
> > * Minimal Modification to the Qemu-Kvm code
> > * We plan to add the page prioritization algo in order to optimise the
> > pre paging algo and background transfer
> 
> Where do you plan to implement? in qemu or in your kernel module?
> This algo could be shared.
> 
> thanks in advance.
> 
> > You can learn a little bit more and see a demo here:
> > http://tinyurl.com/8xa2bgl
> > I hope to be able to provide more detail on the design soon. As well
> > as more concrete demo of the system ( live migration of VM running
> > large  enterprise apps such as ERP or In memory DB)
> > 
> > Note: this is just a step stone as the post copy live migration mainly
> > enable us to validate the architecture design and  code.
> > 
> > Regards
> > Benoit
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > Regards
> > Benoit
> > 
> > 
> > On 12 January 2012 13:59, Avi Kivity <avi@redhat.com> wrote:
> > > On 01/04/2012 05:03 AM, Isaku Yamahata wrote:
> > >> Yes, it's quite doable in user space(qemu) with a kernel-enhancement.
> > >> And it would be easy to convert a separated daemon process into a thread
> > >> in qemu.
> > >>
> > >> I think it should be done out side of qemu process for some reasons.
> > >> (I just repeat same discussion at the KVM-forum because no one remembers
> > >> it)
> > >>
> > >> - ptrace (and its variant)
> > >> ?? Some people want to investigate guest ram on host (qemu stopped or lively).
> > >> ?? For example, enhance crash utility and it will attach qemu process and
> > >> ?? debug guest kernel.
> > >
> > > To debug the guest kernel you don't need to stop qemu itself. ?? I agree
> > > it's a problem for qemu debugging though.
> > >
> > >>
> > >> - core dump
> > >> ?? qemu process may core-dump.
> > >> ?? As postmortem analysis, people want to investigate guest RAM.
> > >> ?? Again enhance crash utility and it will read the core file and analyze
> > >> ?? guest kernel.
> > >> ?? When creating core, the qemu process is already dead.
> > >
> > > Yes, strong point.
> > >
> > >> It precludes the above possibilities to handle fault in qemu process.
> > >
> > > I agree.
> > >
> > >
> > > --
> > > error compiling committee.c: too many arguments to function
> > >
> > > --
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> > 
> > 
> > 
> > -- 
> > " The production of too many useful things results in too many useless people"
> > 
> 
> -- 
> yamahata
> 

-- 
yamahata