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[Xen-devel] RE: [PATCH v3] [linux-3.0+ for xen] tmem: self-ballooning an

To: Konrad Wilk <konrad.wilk@xxxxxxxxxx>
Subject: [Xen-devel] RE: [PATCH v3] [linux-3.0+ for xen] tmem: self-ballooning and frontswap-selfshrinking
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Thu, 30 Jun 2011 15:08:41 -0700 (PDT)
Cc: jeremy@xxxxxxxx, Ian, Campbell <Ian.Campbell@xxxxxxxxxx>, JBeulich@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, Daniel Kiper <dkiper@xxxxxxxxxxxx>
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> From: Konrad Rzeszutek Wilk
> Sent: Thursday, June 30, 2011 3:50 PM
> To: Dan Magenheimer
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; JBeulich@xxxxxxxxxx; jeremy@xxxxxxxx; Ian 
> Campbell; Daniel Kiper
> Subject: Re: [PATCH v3] [linux-3.0+ for xen] tmem: self-ballooning and 
> frontswap-selfshrinking
> > ("tmem") functionality that complement cleancache and frontswap.  Both
> > use control theory to dynamically adjust and optimize memory utilization.
> > Selfballooning controls the in-kernel Xen balloon driver, targeting a goal
> > value (vm_committed_as), thus pushing less frequently used clean
> > page cache pages (through the cleancache code) into Xen tmem where
> > Xen can balance needs across all VMs residing on the physical machine.
> Can this be used by KVM or HyperV code? Can it be made generic? If so, why 
> not?
> If only Xen can use this, what would it entail for other balloon drivers
> to use this? Or is it that they really don't need to b/c none of them
> use the clean cache code?

I'm not an expert on KVM nor on HyperV.  If either becomes capable
of supporting tmem and if the KVM/HyperV equivalent of balloon drivers
are suitable, concepts similar to selfballooning and frontswap-selfshrinking
are likely useful, though it would require quite a bit more study to
try to guess at how one might make the proposed code generic.

I expect to talk to folk at the upcoming KVM Forum to consider
next steps, and another proposed patch (https://lkml.org/lkml/2011/6/30/354)
moves the in-kernel tmem support one step closer to supporting KVM.

It's been awhile since I've communicated with Ky about tmem so I will
re-open that conversation.

But it will probably be months/years before generic'izing this proposed
patch is feasible.  Seems best to cross that bridge later.


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