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

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

On Thu, Nov 02, 2017 at 10:46:20AM +0000, George Dunlap wrote:
> On 11/01/2017 05:10 PM, Konrad Rzeszutek Wilk wrote:
> > 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.
> 
> Right -- so TMEM itself actually consists of this ephemeral and
> non-ephemeral memory pools.  Autoballooning is just a trick to get Linux
> to put the least-used pages into one of the pools.

<nods>
> 
> How about this:
> 
> ---
> Transcendent Memory (tmem) allows the creation of hypervisor memory
> pools which guests can use to store memory rather than caching in its
> own memory or swapping to disk.  Having these in the hypervisor can
> allow more efficient aggregate use of memory across VMs.
> ---

<purrs> Perfect!
> 
>  -George

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