Re: [PATCH v3 0/2] s390/mm: shared zeropage + KVM fixes

[David Hildenbrand]

On 11.04.24 23:28, Andrew Morton wrote:
> On Thu, 11 Apr 2024 18:14:39 +0200 David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> > This series fixes one issue with uffd + shared zeropages on s390x and
> > fixes that "ordinary" KVM guests can make use of shared zeropages again.
> >
> > ...
> >
> > Without the shared zeropage, during (2), the VM would suddenly consume
> > 100 GiB on the migration source and destination. On the migration source,
> > where we don't excpect memory overcommit, we could easilt end up crashing
> > the VM during migration.
> >
> > Independent of that, memory handed back to the hypervisor using "free page
> > reporting" would end up consuming actual memory after the migration on the
> > destination, not getting freed up until reused+freed again.
>
> Is a backport desirable?
>
> If so, the [1/2] Fixes dates back to 2015 and the [2/2] Fixes is from
> 2017.  Is it appropriate that the patches be backported so far back,
> and into different kernel versions?

[2/2] won't be easy to backport to kernels without FAULT_FLAG_UNSHARE, 
so I wouldn't really suggest backports to kernels before that. [1/2] 
might be reasonable to backport, but might require some tweaking (page 
vs. folio).

--
Cheers,

David / dhildenb