Re: [RFC][PATCH 9/9] make kvm mmu shrinker more aggressive

Avi Kivity
2010-06-17T08:37:20Z

On 06/16/2010 06:25 PM, Dave Hansen wrote:
>
>>> If mmu_shrink() has already done a significant amount of
>>> scanning, the use of 'nr_to_scan' inside shrink_kvm_mmu()
>>> will also ensure that we do not over-reclaim when we have
>>> already done a lot of work in this call.
>>>
>>> In the end, this patch defines a "scan" as:
>>> 1. An attempt to acquire a refcount on a 'struct kvm'
>>> 2. freeing a kvm mmu page
>>>
>>> This would probably be most ideal if we can expose some
>>> of the work done by kvm_mmu_remove_some_alloc_mmu_pages()
>>> as also counting as scanning, but I think we have churned
>>> enough for the moment.
>>>
>> It usually removes one page.
>>
> Does it always just go right now and free it, or is there any real
> scanning that has to go on?
>

It picks a page from the tail of the LRU and frees it. There is very
little attempt to keep the LRU in LRU order, though.

We do need a scanner that looks at spte accessed bits if this isn't
going to result in performance losses.

>>> diff -puN arch/x86/kvm/mmu.c~make-shrinker-more-aggressive arch/x86/kvm/mmu.c
>>> --- linux-2.6.git/arch/x86/kvm/mmu.c~make-shrinker-more-aggressive 2010-06-14 11:30:44.000000000 -0700
>>> +++ linux-2.6.git-dave/arch/x86/kvm/mmu.c 2010-06-14 11:38:04.000000000 -0700
>>> @@ -2935,8 +2935,10 @@ static int shrink_kvm_mmu(struct kvm *kv
>>>
>>> idx = srcu_read_lock(&kvm->srcu);
>>> spin_lock(&kvm->mmu_lock);
>>> - if (kvm->arch.n_used_mmu_pages> 0)
>>> - freed_pages = kvm_mmu_remove_some_alloc_mmu_pages(kvm);
>>> + while (nr_to_scan> 0&& kvm->arch.n_used_mmu_pages> 0) {
>>> + freed_pages += kvm_mmu_remove_some_alloc_mmu_pages(kvm);
>>> + nr_to_scan--;
>>> + }
>>>
>>>
>> What tree are you patching?
>>
> These applied to Linus's latest as of yesterday.
>

Please patch against kvm.git master (or next, which is usually a few
unregression-tested patches ahead). This code has changed.

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