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

David Hildenbrand
2024-04-11T21:56:23Z

On 11.04.24 23:28, Andrew Morton wrote:
> On Thu, 11 Apr 2024 18:14:39 +0200 David Hildenbrand <david@redhat.com> 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