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References: <20210726175357.1572951-1-mizhang@google.com> <20210726175357.1572951-4-mizhang@google.com>
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From:   Ben Gardon <bgardon@google.com>
Date:   Mon, 26 Jul 2021 13:41:54 -0700
Message-ID: <CANgfPd8iohgpauQEEAFAQjLPXqHQw1Swguc7C0exHcz985igcw@mail.gmail.com>
Subject: Re: [PATCH v2 3/3] KVM: x86/mmu: Add detailed page size stats
To:     Mingwei Zhang <mizhang@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jing Zhang <jingzhangos@google.com>
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On Mon, Jul 26, 2021 at 10:54 AM Mingwei Zhang <mizhang@google.com> wrote:
>
> Existing KVM code tracks the number of large pages regardless of their
> sizes. Therefore, when large page of 1GB (or larger) is adopted, the
> information becomes less useful because lpages counts a mix of 1G and 2M
> pages.
>
> So remove the lpages since it is easy for user space to aggregate the info.
> Instead, provide a comprehensive page stats of all sizes from 4K to 512G.
>
> Suggested-by: Ben Gardon <bgardon@google.com>
> Suggested-by: Jing Zhang <jingzhangos@google.com>
> Signed-off-by: Mingwei Zhang <mizhang@google.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 10 +++++++++-
>  arch/x86/kvm/mmu.h              |  2 ++
>  arch/x86/kvm/mmu/mmu.c          | 32 +++++++++++++++++++-------------
>  arch/x86/kvm/mmu/tdp_mmu.c      | 15 ++-------------
>  arch/x86/kvm/x86.c              |  7 +++++--
>  5 files changed, 37 insertions(+), 29 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 974cbfb1eefe..2e4b6fd36e62 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1206,9 +1206,17 @@ struct kvm_vm_stat {
>         u64 mmu_recycled;
>         u64 mmu_cache_miss;
>         u64 mmu_unsync;
> -       u64 lpages;
>         u64 nx_lpage_splits;
>         u64 max_mmu_page_hash_collisions;
> +       union {
> +               struct {
> +                       atomic64_t pages_4k;
> +                       atomic64_t pages_2m;
> +                       atomic64_t pages_1g;
> +                       atomic64_t pages_512g;
> +               };
> +               atomic64_t pages[4];
> +       } page_stats;
>  };
>
>  struct kvm_vcpu_stat {
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 83e6c6965f1e..ad5638815311 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -240,4 +240,6 @@ static inline bool kvm_memslots_have_rmaps(struct kvm *kvm)
>         return smp_load_acquire(&kvm->arch.memslots_have_rmaps);
>  }
>
> +void kvm_update_page_stats(struct kvm *kvm, int level, int count);
> +
>  #endif
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 442cc554ebd6..7e0fc760739b 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -588,16 +588,22 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte)
>         return flush;
>  }
>
> +void kvm_update_page_stats(struct kvm *kvm, int level, int count)
> +{
> +       atomic64_add(count, &kvm->stat.page_stats.pages[level - 1]);
> +}
> +
>  /*
>   * Rules for using mmu_spte_clear_track_bits:
>   * It sets the sptep from present to nonpresent, and track the
>   * state bits, it is used to clear the last level sptep.
>   * Returns non-zero if the PTE was previously valid.
>   */
> -static int mmu_spte_clear_track_bits(u64 *sptep)
> +static int mmu_spte_clear_track_bits(struct kvm *kvm, u64 *sptep)
>  {
>         kvm_pfn_t pfn;
>         u64 old_spte = *sptep;
> +       int level = sptep_to_sp(sptep)->role.level;
>
>         if (!spte_has_volatile_bits(old_spte))
>                 __update_clear_spte_fast(sptep, 0ull);
> @@ -607,6 +613,9 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
>         if (!is_shadow_present_pte(old_spte))
>                 return 0;
>
> +       if (is_last_spte(old_spte, level))

You can drop this check since it's part of the contract for calling
this function.

> +               kvm_update_page_stats(kvm, level, -1);
> +
>         pfn = spte_to_pfn(old_spte);
>
>         /*
> @@ -984,9 +993,10 @@ static void __pte_list_remove(u64 *spte, struct kvm_rmap_head *rmap_head)
>         }
>  }
>
> -static void pte_list_remove(struct kvm_rmap_head *rmap_head, u64 *sptep)
> +static void pte_list_remove(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
> +                           u64 *sptep)
>  {
> -       mmu_spte_clear_track_bits(sptep);
> +       mmu_spte_clear_track_bits(kvm, sptep);
>         __pte_list_remove(sptep, rmap_head);
>  }
>
> @@ -1119,7 +1129,7 @@ static u64 *rmap_get_next(struct rmap_iterator *iter)
>
>  static void drop_spte(struct kvm *kvm, u64 *sptep)
>  {
> -       if (mmu_spte_clear_track_bits(sptep))
> +       if (mmu_spte_clear_track_bits(kvm, sptep))
>                 rmap_remove(kvm, sptep);
>  }
>
> @@ -1129,7 +1139,6 @@ static bool __drop_large_spte(struct kvm *kvm, u64 *sptep)
>         if (is_large_pte(*sptep)) {
>                 WARN_ON(sptep_to_sp(sptep)->role.level == PG_LEVEL_4K);
>                 drop_spte(kvm, sptep);
> -               --kvm->stat.lpages;
>                 return true;
>         }
>
> @@ -1386,7 +1395,7 @@ static bool kvm_zap_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
>         while ((sptep = rmap_get_first(rmap_head, &iter))) {
>                 rmap_printk("spte %p %llx.\n", sptep, *sptep);
>
> -               pte_list_remove(rmap_head, sptep);
> +               pte_list_remove(kvm, rmap_head, sptep);
>                 flush = true;
>         }
>
> @@ -1421,13 +1430,13 @@ static bool kvm_set_pte_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
>                 need_flush = 1;
>
>                 if (pte_write(pte)) {
> -                       pte_list_remove(rmap_head, sptep);
> +                       pte_list_remove(kvm, rmap_head, sptep);
>                         goto restart;
>                 } else {
>                         new_spte = kvm_mmu_changed_pte_notifier_make_spte(
>                                         *sptep, new_pfn);
>
> -                       mmu_spte_clear_track_bits(sptep);
> +                       mmu_spte_clear_track_bits(kvm, sptep);
>                         mmu_spte_set(sptep, new_spte);
>                 }
>         }
> @@ -2232,8 +2241,6 @@ static int mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
>         if (is_shadow_present_pte(pte)) {
>                 if (is_last_spte(pte, sp->role.level)) {
>                         drop_spte(kvm, spte);
> -                       if (is_large_pte(pte))
> -                               --kvm->stat.lpages;
>                 } else {
>                         child = to_shadow_page(pte & PT64_BASE_ADDR_MASK);
>                         drop_parent_pte(child, spte);
> @@ -2692,8 +2699,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>         trace_kvm_mmu_set_spte(level, gfn, sptep);
>
>         if (!was_rmapped) {
> -               if (is_large_pte(*sptep))
> -                       ++vcpu->kvm->stat.lpages;
> +               kvm_update_page_stats(vcpu->kvm, level, 1);
>                 rmap_count = rmap_add(vcpu, sptep, gfn);
>                 if (rmap_count > RMAP_RECYCLE_THRESHOLD)
>                         rmap_recycle(vcpu, sptep, gfn);
> @@ -5669,7 +5675,7 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
>                 if (sp->role.direct && !kvm_is_reserved_pfn(pfn) &&
>                     sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
>                                                                pfn, PG_LEVEL_NUM)) {
> -                       pte_list_remove(rmap_head, sptep);
> +                       pte_list_remove(kvm, rmap_head, sptep);
>
>                         if (kvm_available_flush_tlb_with_range())
>                                 kvm_flush_remote_tlbs_with_address(kvm, sp->gfn,
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index cba2ab5db2a0..eae404c15364 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -413,7 +413,6 @@ static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
>         bool was_leaf = was_present && is_last_spte(old_spte, level);
>         bool is_leaf = is_present && is_last_spte(new_spte, level);
>         bool pfn_changed = spte_to_pfn(old_spte) != spte_to_pfn(new_spte);
> -       bool was_large, is_large;
>
>         WARN_ON(level > PT64_ROOT_MAX_LEVEL);
>         WARN_ON(level < PG_LEVEL_4K);
> @@ -472,18 +471,8 @@ static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
>                 return;
>         }
>
> -       /*
> -        * Update large page stats if a large page is being zapped, created, or
> -        * is replacing an existing shadow page.
> -        */
> -       was_large = was_leaf && is_large_pte(old_spte);
> -       is_large = is_leaf && is_large_pte(new_spte);
> -       if (was_large != is_large) {
> -               if (was_large)
> -                       atomic64_sub(1, (atomic64_t *)&kvm->stat.lpages);
> -               else
> -                       atomic64_add(1, (atomic64_t *)&kvm->stat.lpages);
> -       }
> +       if (is_leaf != was_leaf)
> +               kvm_update_page_stats(kvm, level, is_leaf ? 1 : -1);
>
>         if (was_leaf && is_dirty_spte(old_spte) &&
>             (!is_present || !is_dirty_spte(new_spte) || pfn_changed))
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8166ad113fb2..3858d36d3c49 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -235,9 +235,12 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
>         STATS_DESC_COUNTER(VM, mmu_recycled),
>         STATS_DESC_COUNTER(VM, mmu_cache_miss),
>         STATS_DESC_ICOUNTER(VM, mmu_unsync),
> -       STATS_DESC_ICOUNTER(VM, lpages),
>         STATS_DESC_ICOUNTER(VM, nx_lpage_splits),
> -       STATS_DESC_PCOUNTER(VM, max_mmu_page_hash_collisions)
> +       STATS_DESC_PCOUNTER(VM, max_mmu_page_hash_collisions),
> +       STATS_DESC_ICOUNTER(VM, page_stats.pages_4k),
> +       STATS_DESC_ICOUNTER(VM, page_stats.pages_2m),
> +       STATS_DESC_ICOUNTER(VM, page_stats.pages_1g),
> +       STATS_DESC_ICOUNTER(VM, page_stats.pages_512g)
>  };
>  static_assert(ARRAY_SIZE(kvm_vm_stats_desc) ==
>                 sizeof(struct kvm_vm_stat) / sizeof(u64));
> --
> 2.32.0.432.gabb21c7263-goog
>