Re: [RFC][PATCH 4/9] create aggregate kvm_total_used_mmu_pages value

Avi Kivity
2010-06-17T08:43:15Z

On 06/16/2010 06:06 PM, Dave Hansen wrote:
>
>
>>> +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.
>
>

Note, even before you moved the shrinker out of the lock, this was a
problem. kvm_mod_used_mmu_pages() is called not just from the shrinker
code, we zap pages for other reasons as well.

--
error compiling committee.c: too many arguments to function