Re: [PATCH v2 3/3] KVM: x86/mmu: Add detailed page size stats

[Mingwei Zhang <mizhang@google.com>]

Hi David and Ben,

Thank you both for the suggestions. It Makes sense to me and I will
update the patch set with the change added in the next version.

Regards.
-Mingwei

On Tue, Jul 27, 2021 at 8:36 AM David Matlack <dmatlack@google.com> wrote:
>
> On Mon, Jul 26, 2021 at 10:53:57AM -0700, Mingwei Zhang 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))
> > +             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)
>
> FYI this will make the stat names "page_stats.pages_4k",
> "page_stats.pages_2m", etc. Is that ok?
>
> If you want the stat names to be just "pages_4k", "pages_2m", etc. you
> can make the page_stats union anonymous.
>
> >  };
> >  static_assert(ARRAY_SIZE(kvm_vm_stats_desc) ==
> >               sizeof(struct kvm_vm_stat) / sizeof(u64));
> > --
> > 2.32.0.432.gabb21c7263-goog
> >