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

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Message-Id: <20240411142827.d5c3bc401c6536bb1315049a@linux-foundation.org>
Date: Thu, 11 Apr 2024 14:28:27 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, Christian Borntraeger
 <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>, Claudio
 Imbrenda <imbrenda@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Peter Xu <peterx@...hat.com>, Alexander
 Gordeev <agordeev@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>, Andrea Arcangeli
 <aarcange@...hat.com>, kvm@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH v3 0/2] s390/mm: shared zeropage + KVM fixes

On Thu, 11 Apr 2024 18:14:39 +0200 David Hildenbrand <david@...hat.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?