Messages in this thread | | | Date | Wed, 16 Jun 2010 12:24:00 +0300 | From | Avi Kivity <> | Subject | Re: [RFC][PATCH 9/9] make kvm mmu shrinker more aggressive |
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On 06/15/2010 04:55 PM, Dave Hansen wrote: > In a previous patch, we removed the 'nr_to_scan' tracking. > It was not being used to track the number of objects > scanned, so we stopped using it entirely. Here, we > strart using it again. > > The theory here is simple; if we already have the refcount > and the kvm->mmu_lock, then we should do as much work as > possible under the lock. The downside is that we're less > fair about the KVM instances from which we reclaim. Each > call to mmu_shrink() will tend to "pick on" one instance, > after which it gets moved to the end of the list and left > alone for a while. >
That also increases the latency hit, as well as a potential fault storm, on that instance. Spreading out is less efficient, but smoother.
> 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.
> Signed-off-by: Dave Hansen<dave@linux.vnet.ibm.com> > --- > > linux-2.6.git-dave/arch/x86/kvm/mmu.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > 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?
-- error compiling committee.c: too many arguments to function
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