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Message-ID: <CAHVum0dP8PaKGVsg9=9xawj2dOtBnq0YX-SSQ6kkmEjvk4yKKA@mail.gmail.com>
Date: Fri, 13 Jan 2023 09:51:43 -0800
From: Vipin Sharma <vipinsh@...gle.com>
To: Ben Gardon <bgardon@...gle.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
Paolo Bonzini <pbonzini@...hat.com>,
Peter Xu <peterx@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
David Matlack <dmatlack@...gle.com>,
Nagareddy Reddy <nspreddy@...gle.com>
Subject: Re: [RFC 07/14] KVM: x86/MMU: Cleanup shrinker interface with Shadow MMU
On Wed, Dec 21, 2022 at 2:24 PM Ben Gardon <bgardon@...gle.com> wrote:
>
> The MMU shrinker currently only operates on the Shadow MMU, but having
> the entire implemenatation in shadow_mmu.c is awkward since much of the
> function isn't Shadow MMU specific. There has also been talk of changing the
> target of the shrinker to the MMU caches rather than already allocated page
> tables. As a result, it makes sense to move some of the implementation back
> to mmu.c.
>
> No functional change intended.
>
> Signed-off-by: Ben Gardon <bgardon@...gle.com>
> ---
> arch/x86/kvm/mmu/mmu.c | 43 ++++++++++++++++++++++++
> arch/x86/kvm/mmu/shadow_mmu.c | 62 ++++++++---------------------------
> arch/x86/kvm/mmu/shadow_mmu.h | 3 +-
> 3 files changed, 58 insertions(+), 50 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index dd97e346c786..4c45a5b63356 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3147,6 +3147,49 @@ static unsigned long mmu_shrink_count(struct shrinker *shrink,
> return percpu_counter_read_positive(&kvm_total_used_mmu_pages);
> }
>
> +unsigned long mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
> +{
> + struct kvm *kvm;
> + int nr_to_scan = sc->nr_to_scan;
> + unsigned long freed = 0;
> +
> + mutex_lock(&kvm_lock);
> +
> + list_for_each_entry(kvm, &vm_list, vm_list) {
> + /*
> + * Never scan more than sc->nr_to_scan VM instances.
> + * Will not hit this condition practically since we do not try
> + * to shrink more than one VM and it is very unlikely to see
> + * !n_used_mmu_pages so many times.
> + */
> + if (!nr_to_scan--)
> + break;
> +
> + /*
> + * n_used_mmu_pages is accessed without holding kvm->mmu_lock
> + * here. We may skip a VM instance errorneosly, but we do not
> + * want to shrink a VM that only started to populate its MMU
> + * anyway.
> + */
> + if (!kvm->arch.n_used_mmu_pages &&
> + !kvm_shadow_mmu_has_zapped_obsolete_pages(kvm))
> + continue;
> +
> + freed = kvm_shadow_mmu_shrink_scan(kvm, sc->nr_to_scan);
> +
> + /*
> + * unfair on small ones
> + * per-vm shrinkers cry out
> + * sadness comes quickly
> + */
> + list_move_tail(&kvm->vm_list, &vm_list);
> + break;
> + }
> +
> + mutex_unlock(&kvm_lock);
> + return freed;
> +}
> +
> static struct shrinker mmu_shrinker = {
> .count_objects = mmu_shrink_count,
> .scan_objects = mmu_shrink_scan,
> diff --git a/arch/x86/kvm/mmu/shadow_mmu.c b/arch/x86/kvm/mmu/shadow_mmu.c
> index 090b4788f7de..1259c4a3b140 100644
> --- a/arch/x86/kvm/mmu/shadow_mmu.c
> +++ b/arch/x86/kvm/mmu/shadow_mmu.c
> @@ -3147,7 +3147,7 @@ void kvm_zap_obsolete_pages(struct kvm *kvm)
> kvm_mmu_commit_zap_page(kvm, &kvm->arch.zapped_obsolete_pages);
> }
>
> -static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm)
> +bool kvm_shadow_mmu_has_zapped_obsolete_pages(struct kvm *kvm)
Function renaming and removing static should be two separate commits.
> {
> return unlikely(!list_empty_careful(&kvm->arch.zapped_obsolete_pages));
> }
> @@ -3416,60 +3416,24 @@ void kvm_rmap_zap_collapsible_sptes(struct kvm *kvm,
> kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
> }
>
> -unsigned long mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
> +unsigned long kvm_shadow_mmu_shrink_scan(struct kvm *kvm, int pages_to_free)
> {
> - struct kvm *kvm;
> - int nr_to_scan = sc->nr_to_scan;
> unsigned long freed = 0;
> + int idx;
>
> - mutex_lock(&kvm_lock);
> -
> - list_for_each_entry(kvm, &vm_list, vm_list) {
> - int idx;
> - LIST_HEAD(invalid_list);
> -
> - /*
> - * Never scan more than sc->nr_to_scan VM instances.
> - * Will not hit this condition practically since we do not try
> - * to shrink more than one VM and it is very unlikely to see
> - * !n_used_mmu_pages so many times.
> - */
> - if (!nr_to_scan--)
> - break;
> - /*
> - * n_used_mmu_pages is accessed without holding kvm->mmu_lock
> - * here. We may skip a VM instance errorneosly, but we do not
> - * want to shrink a VM that only started to populate its MMU
> - * anyway.
> - */
> - if (!kvm->arch.n_used_mmu_pages &&
> - !kvm_has_zapped_obsolete_pages(kvm))
> - continue;
> -
> - idx = srcu_read_lock(&kvm->srcu);
> - write_lock(&kvm->mmu_lock);
> -
> - if (kvm_has_zapped_obsolete_pages(kvm)) {
> - kvm_mmu_commit_zap_page(kvm,
> - &kvm->arch.zapped_obsolete_pages);
> - goto unlock;
> - }
> + idx = srcu_read_lock(&kvm->srcu);
> + write_lock(&kvm->mmu_lock);
>
> - freed = kvm_mmu_zap_oldest_mmu_pages(kvm, sc->nr_to_scan);
> + if (kvm_shadow_mmu_has_zapped_obsolete_pages(kvm)) {
> + kvm_mmu_commit_zap_page(kvm, &kvm->arch.zapped_obsolete_pages);
> + goto out;
> + }
>
> -unlock:
> - write_unlock(&kvm->mmu_lock);
> - srcu_read_unlock(&kvm->srcu, idx);
> + freed = kvm_mmu_zap_oldest_mmu_pages(kvm, pages_to_free);
>
> - /*
> - * unfair on small ones
> - * per-vm shrinkers cry out
> - * sadness comes quickly
> - */
> - list_move_tail(&kvm->vm_list, &vm_list);
> - break;
> - }
> +out:
> + write_unlock(&kvm->mmu_lock);
> + srcu_read_unlock(&kvm->srcu, idx);
>
> - mutex_unlock(&kvm_lock);
> return freed;
> }
> diff --git a/arch/x86/kvm/mmu/shadow_mmu.h b/arch/x86/kvm/mmu/shadow_mmu.h
> index 20c65a0ea52c..9952aa1e86cf 100644
> --- a/arch/x86/kvm/mmu/shadow_mmu.h
> +++ b/arch/x86/kvm/mmu/shadow_mmu.h
> @@ -99,7 +99,8 @@ void kvm_shadow_mmu_try_split_huge_pages(struct kvm *kvm,
> void kvm_rmap_zap_collapsible_sptes(struct kvm *kvm,
> const struct kvm_memory_slot *slot);
>
> -unsigned long mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc);
> +bool kvm_shadow_mmu_has_zapped_obsolete_pages(struct kvm *kvm);
> +unsigned long kvm_shadow_mmu_shrink_scan(struct kvm *kvm, int pages_to_free);
>
> /* Exports from paging_tmpl.h */
> gpa_t paging32_gva_to_gpa(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> --
> 2.39.0.314.g84b9a713c41-goog
>
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