Re: [Xen-devel] [PATCH RFC v2] Add SUPPORT.md

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Oct 24, 2017 at 04:22:38PM +0100, George Dunlap wrote:
> On Fri, Sep 15, 2017 at 3:51 PM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> >> +### Soft-reset for PV guests
> >
> > s/PV/HVM/
> 
> Is it?  I thought this was for RHEL 5 PV guests to be able to do crash 
> kernels.
> 
> >> +### Transcendent Memory
> >> +
> >> +    Status: Experimental
> >> +
> >> +[XXX Add description]
> >
> > Guests with tmem drivers autoballoon memory out allowing a fluid
> > and dynamic memory allocation - in effect memory overcommit without
> > the need to swap. Only works with Linux guests (as it requires
> > OS drivers).
> 
> But autoballooning doesn't require any support in Xen, right?  I
> thought the TMEM support in Xen was more about the trancendent memory
> backends.

frontends you mean? That is Linux guests when compiled with XEN_TMEM will
balloon down (using the self-shrinker) to using the normal balloon code
(XENMEM_decrease_reservation, XENMEM_populate_physmap) to make the
guest smaller. Then the Linux code starts hitting the case where it starts
swapping memory out - and that is where the tmem comes in and the
pages are swapped out to the hypervisor.

There is also the secondary cache (cleancache) which just puts pages
in the hypervisor temporary cache, kind of like an L3. For that you don't
need ballooning.
> 
> > ..snip..
> >> +### Live Patching
> >> +
> >> +    Status, x86: Supported
> >> +    Status, ARM: Experimental
> >> +
> >> +Compile time disabled
> >
> > for ARM.
> >
> > As the patch will do:
> >
> >  config LIVEPATCH
> > -       bool "Live patching support (TECH PREVIEW)"
> > -       default n
> > +       bool "Live patching support"
> > +       default X86
> >         depends on HAS_BUILD_ID = "y"
> >         ---help---
> >           Allows a running Xen hypervisor to be dynamically patched using
> 
> Ack
> 
>  -George
> 
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