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

[Avi Kivity]

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

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