Re: [Patch v4 06/18] KVM: x86/mmu: Shrink split_shadow_page_cache via MMU shrinker

[Zhi Wang <zhi.wang.linux@gmail.com>]

On Mon,  6 Mar 2023 14:41:15 -0800
Vipin Sharma <vipinsh@google.com> wrote:

> Use MMU shrinker to free unused pages in split_shadow_page_cache.
> Refactor the code and make common function to try emptying the page cache.
> 
> Signed-off-by: Vipin Sharma <vipinsh@google.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 34 +++++++++++++++++++++-------------
>  1 file changed, 21 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 0ebb8a2eaf47..73a0ac9c11ce 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -6696,13 +6696,24 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen)
>  	}
>  }
>  

After adding the lock in the kvm_mmu_memory_cache, the cache_lock doesn't need
to be passed here and in mmu_shrink_scan().

> +static int mmu_memory_cache_try_empty(struct kvm_mmu_memory_cache *cache,
> +				      struct mutex *cache_lock)
> +{
> +	int freed = 0;
> +
> +	if (mutex_trylock(cache_lock)) {
> +		freed = cache->nobjs;
> +		kvm_mmu_empty_memory_cache(cache);
> +		mutex_unlock(cache_lock);
> +	}
> +	return freed;
> +}
> +
>  static unsigned long mmu_shrink_scan(struct shrinker *shrink,
>  				     struct shrink_control *sc)
>  {
>  	struct kvm *kvm, *next_kvm, *first_kvm = NULL;
> -	struct kvm_mmu_memory_cache *cache;
>  	unsigned long i, freed = 0;
> -	struct mutex *cache_lock;
>  	struct kvm_vcpu *vcpu;
>  
>  	mutex_lock(&kvm_lock);
> @@ -6716,18 +6727,15 @@ static unsigned long mmu_shrink_scan(struct shrinker *shrink,
>  		list_move_tail(&kvm->vm_list, &vm_list);
>  
>  		kvm_for_each_vcpu(i, vcpu, kvm) {
> -			cache = &vcpu->arch.mmu_shadow_page_cache;
> -			cache_lock = &vcpu->arch.mmu_shadow_page_cache_lock;
> -			if (mutex_trylock(cache_lock)) {
> -				if (cache->nobjs) {
> -					freed += cache->nobjs;
> -					kvm_mmu_empty_memory_cache(cache);
> -				}
> -				mutex_unlock(cache_lock);
> -				if (freed >= sc->nr_to_scan)
> -					goto out;
> -			}
> +			freed += mmu_memory_cache_try_empty(&vcpu->arch.mmu_shadow_page_cache,
> +							    &vcpu->arch.mmu_shadow_page_cache_lock);
> +			if (freed >= sc->nr_to_scan)
> +				goto out;
>  		}
> +		freed += mmu_memory_cache_try_empty(&kvm->arch.split_shadow_page_cache,
> +						    &kvm->slots_lock);
> +		if (freed >= sc->nr_to_scan)
> +			goto out;
>  	}
>  out:
>  	mutex_unlock(&kvm_lock);