Re: [Xen-devel] Xen balloon driver improvement (version 1)

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Oct 23, 2014 at 05:04:50PM +0100, Ian Campbell wrote:
[...]
> > >> For example I know FreeBSD has contigmalloc(9)[1] which I think could be
> > >> used to achieve this. You could start asking for pages starting at
> > >> maxpfn and go down from there, keeping fragmentation at a minimum.
> > >>
> > >> [1]
> > >> https://www.freebsd.org/cgi/man.cgi?query=contigmalloc&apropos=0&sektion=0&manpath=FreeBSD+10.1-RELEASE&arch=default&format=html
> > >>
> > > 
> > > Good point. Just that Linux doesn't have a counterpart, not that I know
> > > of. Memblock infrastructure looks similar but it's supposed to be used
> > > when initialising kernel.
> > > 
> > > Even if Linux has similar API, it's still less desirable because to
> > > satisfy a contiguous PA allocation, the system needs to be relative
> > > quiet (if NO_WAIT / ATOMIC is set), or the API needs to sleep for
> > > indefinite period (wait for memory subsystem to squeeze out pages).
> > 
> > There's no restriction on the time it might take for a guest to balloon
> > out. IMHO I would rather add a new interface to the Linux VM subsystem
> > that tries to accomplish this rather than adding a bunch of logic
> > specific to the balloon driver.
> 
> AIUI this already exists and Wei is simply hooking up the necessary
> callbacks into the balloon driver.
> 

That's right.

> Ian.

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