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    SubjectRe: [RFC][PATCH 4/9] create aggregate kvm_total_used_mmu_pages value
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    On Wed, 2010-06-16 at 11:48 +0300, Avi Kivity wrote:
    > On 06/15/2010 04:55 PM, Dave Hansen wrote:
    > > +/*
    > > + * This value is the sum of all of the kvm instances's
    > > + * kvm->arch.n_used_mmu_pages values. We need a global,
    > > + * aggregate version in order to make the slab shrinker
    > > + * faster
    > > + */
    > > +static unsigned int kvm_total_used_mmu_pages;
    > >
    >
    > The variable needs to be at the top of the file.

    Gotcha, will do.

    > > +static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, int nr)
    > > +{
    > > + kvm->arch.n_used_mmu_pages += nr;
    > > + kvm_total_used_mmu_pages += nr;
    > >
    >
    > Needs an atomic operation, since there's no global lock here. To avoid
    > bouncing this cacheline around, make the variable percpu and make
    > readers take a sum across all cpus. Side benefit is that you no longer
    > need an atomic but a local_t, which is considerably cheaper.

    That's a good point. All of the modifications are done under locks, but
    the fast path isn't any more. I'll fix it up.

    -- Dave



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