linux-kernel - Re: [Patch v4 14/18] KVM: mmu: Initialize kvm_mmu_memory_cache.gfp_zero to __GFP

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Date:   Tue, 28 Mar 2023 16:13:07 -0700
From:   David Matlack <dmatlack@...gle.com>
To:     Vipin Sharma <vipinsh@...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 14/18] KVM: mmu: Initialize kvm_mmu_memory_cache.gfp_zero
 to __GFP_ZERO by default

On Tue, Mar 28, 2023 at 10:31 AM Vipin Sharma <vipinsh@...gle.com> wrote:
>
> On Thu, Mar 23, 2023 at 3:28 PM David Matlack <dmatlack@...gle.com> wrote:
> >
> > On Mon, Mar 06, 2023 at 02:41:23PM -0800, Vipin Sharma wrote:
> > > Set __GFP_ZERO to gfp_zero in default initizliation of struct
> > > kvm_mmu_memory_cache{}
> > >
> > > All of the users of default initialization code of struct
> > > kvm_mmu_memory_cache{} explicitly sets gfp_zero to __GFP_ZERO. This can
> > > be moved to common initialization logic.
> >
> > If that were true we could get rid of gfp_zero entirely and hard-code
> > __GFP_ZERO in the memory allocator! mmu_shadowed_info_cache is the one
> > that does not set __GFP_ZERO.
> >
>
> Can we use __GFP_ZERO for mmu_shadowed_info_cache?

Yes but doing so would add CPU cost to zero the memory on allocation.
Someone would need to do some performance testing to confirm that the
cost of zeroing is acceptable.

> Also, MIPS doesn't
> use __GFP_ZERO, I think it might be a missed thing in MIPS rather than
> intentional.