linux-kernel - Re: [PATCH v5 2/4] KVM: mmu: add a helper to account memory used by KVM MMU.

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Message-ID: <CAJD7tkbqAignkN-Vh3A3gyBV_n_gZDBpM56r9HiXrYG+F0v8wg@mail.gmail.com>
Date:   Mon, 27 Jun 2022 09:28:36 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Cgroups <cgroups@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v5 2/4] KVM: mmu: add a helper to account memory used by
 KVM MMU.

On Mon, Jun 27, 2022 at 9:20 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Mon, Jun 06, 2022, Yosry Ahmed wrote:
> > Add a helper to account pages used by KVM for page tables in secondary
> > pagetable stats. This function will be used by subsequent patches in
> > different archs.
> >
> > Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> > ---
> >  include/linux/kvm_host.h | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 883e86ec8e8c4..645585f3a4bed 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -2246,6 +2246,15 @@ static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
> >  }
> >  #endif /* CONFIG_KVM_XFER_TO_GUEST_WORK */
> >
> > +/*
> > + * If nr > 1, we assume virt is the address of the first page of a block of
>
> But what if @nr is -2, which is technically less than 1?  :-)
>
> > + * pages that were allocated together (i.e accounted together).
>
> Don't document assumptions, document the rules.  And avoid "we", pronouns are
> ambiguous, e.g. is "we" the author, or KVM, or something else entirely?
>
> /*
>  * If more than one page is being (un)accounted, @virt must be the address of
>  * the first page of a block of pages what were allocated together.
>  */
>

Looks much better, I will use that in the next version.

Thanks!

>
> > + */
> > +static inline void kvm_account_pgtable_pages(void *virt, int nr)
> > +{
> > +     mod_lruvec_page_state(virt_to_page(virt), NR_SECONDARY_PAGETABLE, nr);
> > +}
> > +
> >  /*
> >   * This defines how many reserved entries we want to keep before we
> >   * kick the vcpu to the userspace to avoid dirty ring full.  This
> > --
> > 2.36.1.255.ge46751e96f-goog
> >