Re: [PATCH v5 08/23] KVM: s390: KVM page table management functions: allocation

[Janosch Frank]

On 11/24/25 13:41, Claudio Imbrenda wrote:
> On Mon, 24 Nov 2025 13:27:24 +0100
> Janosch Frank <frankja@xxxxxxxxxxxxx> wrote:
>
> > On 11/24/25 12:55, Claudio Imbrenda wrote:
> > > Add page table management functions to be used for KVM guest (gmap)
> > > page tables.
> > >
> > > This patch adds the boilerplate and functions for the allocation and
> > > deallocation of DAT tables.
> > >
> > > Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> >
> > What's the cache for, why did you add it?
>
> the cache is needed to allocate memory when we can sleep (to avoid
> atomic allocations), and use it when holding spinlocks (when we can't
> sleep).
>
> this is similar to what other architectures do, except that in their
> case they only have one type of page table to worry about, we need at
> least 3 types of objects.
>
> unlike other architectures, allocations from the cache can fail, and
> the calling code needs to handle failures (e.g. by replenishing the
> cache and trying again)

Well, this information should make it into this patch, either into the 
description or in the body.

> > > ---
> > >    arch/s390/kvm/Makefile     |   1 +
> > >    arch/s390/kvm/dat.c        | 103 +++++++++++++++++++++++++++++++++++++
> > >    arch/s390/kvm/dat.h        |  77 +++++++++++++++++++++++++++
> > >    arch/s390/mm/page-states.c |   1 +
> > >    4 files changed, 182 insertions(+)
> > >    create mode 100644 arch/s390/kvm/dat.c