On Thu, Dec 29, 2022 at 1:55 PM David Matlack <dmatlack@xxxxxxxxxx> wrote: > > On Wed, Dec 21, 2022 at 06:34:49PM -0800, Vipin Sharma wrote: > > mmu_shrink_scan() is very disruptive to VMs. It picks the first > > VM in the vm_list, zaps the oldest page which is most likely an upper > > level SPTEs and most like to be reused. Prior to TDP MMU, this is even > > more disruptive in nested VMs case, considering L1 SPTEs will be the > > oldest even though most of the entries are for L2 SPTEs. > > > > As discussed in > > https://lore.kernel.org/lkml/Y45dldZnI6OIf+a5@xxxxxxxxxx/ > > shrinker logic has not be very useful in actually keeping VMs performant > > and reducing memory usage. > > > > Change mmu_shrink_scan() to free pages from the vCPU's shadow page > > cache. Freeing pages from cache doesn't cause vCPU exits, therefore, a > > VM's performance should not be affected. > > Can you split this commit up? e.g. First drop the old shrinking logic in > one commit (but leave the shrinking infrastructure in place). Then a > commit to make the shrinker free the per-vCPU shadow page caches. And > then perhaps another to make the shrinker free the per-VM shadow page > cache used for eager splitting. > Sounds good, I will separate it in two parts, one for dropping old logic, one for adding per vcpu shadow page caches. Patch 3 is enabling shrinkerto free per-VM shadow page. > > > > This also allows to change cache capacities without worrying too much > > about high memory usage in cache. > > > > Tested this change by running dirty_log_perf_test while dropping cache > > via "echo 2 > /proc/sys/vm/drop_caches" at 1 second interval > > continuously. There were WARN_ON(!mc->nobjs) messages printed in kernel > > logs from kvm_mmu_memory_cache_alloc(), which is expected. > > > > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> > > Signed-off-by: Vipin Sharma <vipinsh@xxxxxxxxxx> > > --- > > arch/x86/include/asm/kvm_host.h | 5 + > > arch/x86/kvm/mmu/mmu.c | 163 +++++++++++++++++++------------- > > arch/x86/kvm/mmu/mmu_internal.h | 2 + > > arch/x86/kvm/mmu/tdp_mmu.c | 3 +- > > include/linux/kvm_host.h | 1 + > > virt/kvm/kvm_main.c | 11 ++- > > 6 files changed, 114 insertions(+), 71 deletions(-) > > > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > > index aa4eb8cfcd7e..89cc809e4a00 100644 > > --- a/arch/x86/include/asm/kvm_host.h > > +++ b/arch/x86/include/asm/kvm_host.h > > @@ -786,6 +786,11 @@ struct kvm_vcpu_arch { > > struct kvm_mmu_memory_cache mmu_shadowed_info_cache; > > struct kvm_mmu_memory_cache mmu_page_header_cache; > > > > + /* > > + * Protects change in size of mmu_shadow_page_cache cache. > > + */ > > + spinlock_t mmu_shadow_page_cache_lock; > > + > > /* > > * QEMU userspace and the guest each have their own FPU state. > > * In vcpu_run, we switch between the user and guest FPU contexts. > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > > index 254bc46234e0..157417e1cb6e 100644 > > --- a/arch/x86/kvm/mmu/mmu.c > > +++ b/arch/x86/kvm/mmu/mmu.c > > @@ -164,7 +164,10 @@ struct kvm_shadow_walk_iterator { > > > > static struct kmem_cache *pte_list_desc_cache; > > struct kmem_cache *mmu_page_header_cache; > > -static struct percpu_counter kvm_total_used_mmu_pages; > > +/* > > + * Total number of unused pages in MMU shadow page cache. > > + */ > > +static struct percpu_counter kvm_total_unused_mmu_pages; > > > > static void mmu_spte_set(u64 *sptep, u64 spte); > > > > @@ -655,6 +658,22 @@ static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu) > > } > > } > > > > +static int mmu_topup_sp_memory_cache(struct kvm_mmu_memory_cache *cache, > > + spinlock_t *cache_lock) > > +{ > > + int orig_nobjs; > > + int r; > > + > > + spin_lock(cache_lock); > > + orig_nobjs = cache->nobjs; > > + r = kvm_mmu_topup_memory_cache(cache, PT64_ROOT_MAX_LEVEL); > > + if (orig_nobjs != cache->nobjs) > > + percpu_counter_add(&kvm_total_unused_mmu_pages, > > + (cache->nobjs - orig_nobjs)); > > + spin_unlock(cache_lock); > > + return r; > > +} > > + > > static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect) > > { > > int r; > > @@ -664,8 +683,8 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect) > > 1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM); > > if (r) > > return r; > > - r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_shadow_page_cache, > > - PT64_ROOT_MAX_LEVEL); > > + r = mmu_topup_sp_memory_cache(&vcpu->arch.mmu_shadow_page_cache, > > + &vcpu->arch.mmu_shadow_page_cache_lock); > > if (r) > > return r; > > if (maybe_indirect) { > > @@ -678,10 +697,25 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect) > > PT64_ROOT_MAX_LEVEL); > > } > > > > +static void mmu_free_sp_memory_cache(struct kvm_mmu_memory_cache *cache, > > + spinlock_t *cache_lock) > > +{ > > + int orig_nobjs; > > + > > + spin_lock(cache_lock); > > + orig_nobjs = cache->nobjs; > > + kvm_mmu_free_memory_cache(cache); > > + if (orig_nobjs) > > + percpu_counter_sub(&kvm_total_unused_mmu_pages, orig_nobjs); > > + > > + spin_unlock(cache_lock); > > +} > > It would be nice to avoid adding these wrapper functions. > > Once you add a mutex to protect the caches from being freed while vCPUs > are in the middle of a page fault you can drop the spin lock. After that > the only reason to have these wrappers is to update > kvm_total_unused_mmu_pages. > > Do we really need kvm_total_unused_mmu_pages? Why not just dynamically > calculate the number of of unused pages in mmu_shrink_count()? Or just > estimate the count, e.g. num_vcpus * KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE? > Or have per-VM or per-vCPU shrinkers to avoid needing to do any > aggregation? > I think we can drop this, by default we can return num_kvms * num_vcpus * nodes * KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE Whenever mmu_shrink_scan() is called if there are no pages to free then return SHRINK_STOP which will stop any subsequent calls during that time. > > + > > static void mmu_free_memory_caches(struct kvm_vcpu *vcpu) > > { > > kvm_mmu_free_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache); > > - kvm_mmu_free_memory_cache(&vcpu->arch.mmu_shadow_page_cache); > > + mmu_free_sp_memory_cache(&vcpu->arch.mmu_shadow_page_cache, > > + &vcpu->arch.mmu_shadow_page_cache_lock); > > kvm_mmu_free_memory_cache(&vcpu->arch.mmu_shadowed_info_cache); > > mmu_shadowed_info_cache can be freed by the shrinker as well. > > > kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_header_cache); > > } > > @@ -1693,27 +1727,15 @@ static int is_empty_shadow_page(u64 *spt) > > } > > #endif > > > > -/* > > - * This value is the sum of all of the kvm instances's > > - * kvm->arch.n_used_mmu_pages values. We need a global, > > - * aggregate version in order to make the slab shrinker > > - * faster > > - */ > > -static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, long nr) > > -{ > > - kvm->arch.n_used_mmu_pages += nr; > > - percpu_counter_add(&kvm_total_used_mmu_pages, nr); > > -} > > - > > static void kvm_account_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp) > > { > > - kvm_mod_used_mmu_pages(kvm, +1); > > + kvm->arch.n_used_mmu_pages++; > > kvm_account_pgtable_pages((void *)sp->spt, +1); > > } > > > > static void kvm_unaccount_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp) > > { > > - kvm_mod_used_mmu_pages(kvm, -1); > > + kvm->arch.n_used_mmu_pages--; > > kvm_account_pgtable_pages((void *)sp->spt, -1); > > } > > > > @@ -2150,8 +2172,31 @@ struct shadow_page_caches { > > struct kvm_mmu_memory_cache *page_header_cache; > > struct kvm_mmu_memory_cache *shadow_page_cache; > > struct kvm_mmu_memory_cache *shadowed_info_cache; > > + /* > > + * Protects change in size of shadow_page_cache cache. > > + */ > > + spinlock_t *shadow_page_cache_lock; > > }; > > > > +void *kvm_mmu_sp_memory_cache_alloc(struct kvm_mmu_memory_cache *shadow_page_cache, > > + spinlock_t *cache_lock) > > +{ > > + int orig_nobjs; > > + void *page; > > + > > + if (!cache_lock) { > > + spin_lock(cache_lock); > > + orig_nobjs = shadow_page_cache->nobjs; > > + } > > + page = kvm_mmu_memory_cache_alloc(shadow_page_cache); > > + if (!cache_lock) { > > + if (orig_nobjs) > > + percpu_counter_dec(&kvm_total_unused_mmu_pages); > > + spin_unlock(cache_lock); > > + } > > + return page; > > +} > > + > > static struct kvm_mmu_page *kvm_mmu_alloc_shadow_page(struct kvm *kvm, > > struct shadow_page_caches *caches, > > gfn_t gfn, > > @@ -2161,7 +2206,8 @@ static struct kvm_mmu_page *kvm_mmu_alloc_shadow_page(struct kvm *kvm, > > struct kvm_mmu_page *sp; > > > > sp = kvm_mmu_memory_cache_alloc(caches->page_header_cache); > > - sp->spt = kvm_mmu_memory_cache_alloc(caches->shadow_page_cache); > > + sp->spt = kvm_mmu_sp_memory_cache_alloc(caches->shadow_page_cache, > > + caches->shadow_page_cache_lock); > > if (!role.direct) > > sp->shadowed_translation = kvm_mmu_memory_cache_alloc(caches->shadowed_info_cache); > > > > @@ -2218,6 +2264,7 @@ static struct kvm_mmu_page *kvm_mmu_get_shadow_page(struct kvm_vcpu *vcpu, > > .page_header_cache = &vcpu->arch.mmu_page_header_cache, > > .shadow_page_cache = &vcpu->arch.mmu_shadow_page_cache, > > .shadowed_info_cache = &vcpu->arch.mmu_shadowed_info_cache, > > + .shadow_page_cache_lock = &vcpu->arch.mmu_shadow_page_cache_lock > > }; > > > > return __kvm_mmu_get_shadow_page(vcpu->kvm, vcpu, &caches, gfn, role); > > @@ -5916,6 +5963,7 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu) > > vcpu->arch.mmu_page_header_cache.gfp_zero = __GFP_ZERO; > > > > vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO; > > + spin_lock_init(&vcpu->arch.mmu_shadow_page_cache_lock); > > > > vcpu->arch.mmu = &vcpu->arch.root_mmu; > > vcpu->arch.walk_mmu = &vcpu->arch.root_mmu; > > @@ -6051,11 +6099,6 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm) > > kvm_tdp_mmu_zap_invalidated_roots(kvm); > > } > > > > -static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm) > > -{ > > - return unlikely(!list_empty_careful(&kvm->arch.zapped_obsolete_pages)); > > -} > > - > > static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm, > > struct kvm_memory_slot *slot, > > struct kvm_page_track_notifier_node *node) > > @@ -6277,6 +6320,7 @@ static struct kvm_mmu_page *shadow_mmu_get_sp_for_split(struct kvm *kvm, u64 *hu > > /* Direct SPs do not require a shadowed_info_cache. */ > > caches.page_header_cache = &kvm->arch.split_page_header_cache; > > caches.shadow_page_cache = &kvm->arch.split_shadow_page_cache; > > + caches.shadow_page_cache_lock = NULL; > > > > /* Safe to pass NULL for vCPU since requesting a direct SP. */ > > return __kvm_mmu_get_shadow_page(kvm, NULL, &caches, gfn, role); > > @@ -6646,66 +6690,49 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen) > > static unsigned long > > mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) > > { > > - struct kvm *kvm; > > - int nr_to_scan = sc->nr_to_scan; > > + struct kvm_mmu_memory_cache *cache; > > + struct kvm *kvm, *first_kvm = NULL; > > unsigned long freed = 0; > > + /* spinlock for memory cache */ > > + spinlock_t *cache_lock; > > + struct kvm_vcpu *vcpu; > > + unsigned long i; > > > > 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--) > > + if (first_kvm == kvm) > > 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; > > + if (!first_kvm) > > + first_kvm = kvm; > > + list_move_tail(&kvm->vm_list, &vm_list); > > > > - idx = srcu_read_lock(&kvm->srcu); > > - write_lock(&kvm->mmu_lock); > > + kvm_for_each_vcpu(i, vcpu, kvm) { > > What protects this from racing with vCPU creation/deletion? > > > + cache = &vcpu->arch.mmu_shadow_page_cache; > > + cache_lock = &vcpu->arch.mmu_shadow_page_cache_lock; > > + if (READ_ONCE(cache->nobjs)) { > > + spin_lock(cache_lock); > > + freed += kvm_mmu_empty_memory_cache(cache); > > + spin_unlock(cache_lock); > > + } > > What about freeing kvm->arch.split_shadow_page_cache as well? > > > > > - if (kvm_has_zapped_obsolete_pages(kvm)) { > > - kvm_mmu_commit_zap_page(kvm, > > - &kvm->arch.zapped_obsolete_pages); > > - goto unlock; > > } > > > > - freed = kvm_mmu_zap_oldest_mmu_pages(kvm, sc->nr_to_scan); > > - > > -unlock: > > - write_unlock(&kvm->mmu_lock); > > - srcu_read_unlock(&kvm->srcu, idx); > > - > > - /* > > - * unfair on small ones > > - * per-vm shrinkers cry out > > - * sadness comes quickly > > - */ > > - list_move_tail(&kvm->vm_list, &vm_list); > > - break; > > + if (freed >= sc->nr_to_scan) > > + break; > > } > > > > + if (freed) > > + percpu_counter_sub(&kvm_total_unused_mmu_pages, freed); > > mutex_unlock(&kvm_lock); > > + percpu_counter_sync(&kvm_total_unused_mmu_pages); > > return freed; > > } > > > > static unsigned long > > mmu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) > > { > > - return percpu_counter_read_positive(&kvm_total_used_mmu_pages); > > + return percpu_counter_sum_positive(&kvm_total_unused_mmu_pages); > > } > > > > static struct shrinker mmu_shrinker = { > > @@ -6820,7 +6847,7 @@ int kvm_mmu_vendor_module_init(void) > > if (!mmu_page_header_cache) > > goto out; > > > > - if (percpu_counter_init(&kvm_total_used_mmu_pages, 0, GFP_KERNEL)) > > + if (percpu_counter_init(&kvm_total_unused_mmu_pages, 0, GFP_KERNEL)) > > goto out; > > > > ret = register_shrinker(&mmu_shrinker, "x86-mmu"); > > @@ -6830,7 +6857,7 @@ int kvm_mmu_vendor_module_init(void) > > return 0; > > > > out_shrinker: > > - percpu_counter_destroy(&kvm_total_used_mmu_pages); > > + percpu_counter_destroy(&kvm_total_unused_mmu_pages); > > out: > > mmu_destroy_caches(); > > return ret; > > @@ -6847,7 +6874,7 @@ void kvm_mmu_destroy(struct kvm_vcpu *vcpu) > > void kvm_mmu_vendor_module_exit(void) > > { > > mmu_destroy_caches(); > > - percpu_counter_destroy(&kvm_total_used_mmu_pages); > > + percpu_counter_destroy(&kvm_total_unused_mmu_pages); > > unregister_shrinker(&mmu_shrinker); > > } > > > > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h > > index ac00bfbf32f6..c2a342028b6a 100644 > > --- a/arch/x86/kvm/mmu/mmu_internal.h > > +++ b/arch/x86/kvm/mmu/mmu_internal.h > > @@ -325,4 +325,6 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc); > > void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp); > > void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp); > > > > +void *kvm_mmu_sp_memory_cache_alloc(struct kvm_mmu_memory_cache *shadow_page_cache, > > + spinlock_t *cache_lock); > > #endif /* __KVM_X86_MMU_INTERNAL_H */ > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > > index 764f7c87286f..4974fa96deff 100644 > > --- a/arch/x86/kvm/mmu/tdp_mmu.c > > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > > @@ -264,7 +264,8 @@ static struct kvm_mmu_page *tdp_mmu_alloc_sp(struct kvm_vcpu *vcpu) > > struct kvm_mmu_page *sp; > > > > sp = kvm_mmu_memory_cache_alloc(&vcpu->arch.mmu_page_header_cache); > > - sp->spt = kvm_mmu_memory_cache_alloc(&vcpu->arch.mmu_shadow_page_cache); > > + sp->spt = kvm_mmu_sp_memory_cache_alloc(&vcpu->arch.mmu_shadow_page_cache, > > + &vcpu->arch.mmu_shadow_page_cache_lock); > > > > return sp; > > } > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > index 01aad8b74162..efd9b38ea9a2 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -1362,6 +1362,7 @@ void kvm_flush_remote_tlbs(struct kvm *kvm); > > int kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min); > > int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity, int min); > > int kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc); > > +int kvm_mmu_empty_memory_cache(struct kvm_mmu_memory_cache *mc); > > void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc); > > void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc); > > #endif > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index 13e88297f999..f2d762878b97 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -438,8 +438,10 @@ int kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc) > > return mc->nobjs; > > } > > > > -void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc) > > +int kvm_mmu_empty_memory_cache(struct kvm_mmu_memory_cache *mc) > > { > > + int freed = mc->nobjs; > > + > > while (mc->nobjs) { > > if (mc->kmem_cache) > > kmem_cache_free(mc->kmem_cache, mc->objects[--mc->nobjs]); > > @@ -447,8 +449,13 @@ void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc) > > free_page((unsigned long)mc->objects[--mc->nobjs]); > > } > > > > - kvfree(mc->objects); > > + return freed; > > +} > > > > +void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc) > > +{ > > + kvm_mmu_empty_memory_cache(mc); > > + kvfree(mc->objects); > > mc->objects = NULL; > > mc->capacity = 0; > > } > > -- > > 2.39.0.314.g84b9a713c41-goog > >
