linux-kernel - Re: [Patch v4 15/18] KVM: mmu: Add NUMA node support in struct kvm_mmu_memory

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Date:   Tue, 28 Mar 2023 10:50:46 -0700
From:   Vipin Sharma <vipinsh@...gle.com>
To:     David Matlack <dmatlack@...gle.com>
Cc:     seanjc@...gle.com, pbonzini@...hat.com, bgardon@...gle.com,
        jmattson@...gle.com, mizhang@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Patch v4 15/18] KVM: mmu: Add NUMA node support in struct kvm_mmu_memory_cache{}

On Thu, Mar 23, 2023 at 3:30 PM David Matlack <dmatlack@...gle.com> wrote:
>
> On Mon, Mar 06, 2023 at 02:41:24PM -0800, Vipin Sharma wrote:
> > Add NUMA node id variable in struct kvm_mmu_memory_cache{}. This
> > variable denotes preferable NUMA node from which memory will be
> > allocated under this memory cache.
> >
> > Set this variable to NUMA_NO_NODE if there is no preferred node.
> >
> > MIPS doesn't do any sort of initializatino of struct
> > kvm_mmu_memory_cache{}. Keep things similar in MIPS by setting gfp_zero
> > to 0 as INIT_KVM_MMU_MEMORY_CACHE() will initialize it to __GFP_ZERO.
> >
> > "node" cannot be left as 0, as 0 is a valid NUMA node value.
> >
> > Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
> > ---
> >  arch/mips/kvm/mips.c      | 3 +++
> >  include/linux/kvm_types.h | 3 +++
> >  2 files changed, 6 insertions(+)
> >
> > diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> > index 36c8991b5d39..5ec5ce919918 100644
> > --- a/arch/mips/kvm/mips.c
> > +++ b/arch/mips/kvm/mips.c
> > @@ -294,6 +294,9 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> >                    HRTIMER_MODE_REL);
> >       vcpu->arch.comparecount_timer.function = kvm_mips_comparecount_wakeup;
> >
> > +     INIT_KVM_MMU_MEMORY_CACHE(&vcpu->arch.mmu_page_cache);
> > +     vcpu->arch.mmu_page_cache.gfp_zero = 0;
>
> Oh MIPS is here. Why isn't MIPS covered in the previous commits?
>

Because this is the patch where MIPS get impacted. MIPS doesn't
initialize gfp_zero, so there was no need to change the code in MIPS.
However, with the addition of "node" in kvm_mmu_memory_cache{} in this
patch, we need initialization in MIPS to (1) Set  node to NUMA_NO_NODE
as 0 is now a valid value, and (2) INIT_KVM_MMU_MEMORY_CACHE() will
set gfp_zero to __GFP_ZERO which is different than existing code in
MIPS to keep it 0.

I asked MIPS maintainers in the previous version to see if GFP_ZERO
can be added but didn't get any response.
https://lore.kernel.org/lkml/CAHVum0c+17Z-RbGAFdU-xmRejDjDQ+MKOfN4XaObh2SwgWAjLg@mail.gmail.com/

> > +
> >       /*
> >        * Allocate space for host mode exception handlers that handle
> >        * guest mode exits
> > diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
> > index 5da7953532ce..b2a405c8e629 100644
> > --- a/include/linux/kvm_types.h
> > +++ b/include/linux/kvm_types.h
> > @@ -97,10 +97,13 @@ struct kvm_mmu_memory_cache {
> >       struct kmem_cache *kmem_cache;
> >       int capacity;
> >       void **objects;
> > +     /* Preferred NUMA node of memory allocation. */
> > +     int node;
> >  };
> >
> >  #define KVM_MMU_MEMORY_CACHE_INIT() {        \
> >       .gfp_zero = __GFP_ZERO,         \
> > +     .node = NUMA_NO_NODE,           \
> >  }
> >
> >  #define KVM_MMU_MEMORY_CACHE(_name) \
> > --
> > 2.40.0.rc0.216.gc4246ad0f0-goog
> >