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KVM: x86/mmu: Batch zap MMU pages when shrinking the slab

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Use the recently introduced kvm_mmu_zap_oldest_mmu_pages() to batch zap
MMU pages when shrinking a slab.  This fixes a long standing issue where
KVM's shrinker implementation is completely ineffective due to zapping
only a single page.  E.g. without batch zapping, forcing a scan via
drop_caches basically has no impact on a VM with ~2k shadow pages.  With
batch zapping, the number of shadow pages can be reduced to a few
hundred pages in one or two runs of drop_caches.

Note, if the default batch size (currently 128) is problematic, e.g.
zapping 128 pages holds mmu_lock for too long, KVM can bound the batch
size by setting @batch in mmu_shrinker.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200623193542.7554-4-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2020-06-23 12:35:41 -07:00 committed by Paolo Bonzini
parent 6b82ef2c9c
commit ebdb292dac
1 changed files with 1 additions and 16 deletions
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17
arch/x86/kvm/mmu/mmu.c
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@ -2816,19 +2816,6 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
}
}
static bool prepare_zap_oldest_mmu_page(struct kvm *kvm,
struct list_head *invalid_list)
{
struct kvm_mmu_page *sp;
if (list_empty(&kvm->arch.active_mmu_pages))
return false;
sp = list_last_entry(&kvm->arch.active_mmu_pages,
struct kvm_mmu_page, link);
return kvm_mmu_prepare_zap_page(kvm, sp, invalid_list);
}
static unsigned long kvm_mmu_zap_oldest_mmu_pages(struct kvm *kvm,
unsigned long nr_to_zap)
{
@ -6116,9 +6103,7 @@ mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
goto unlock;
}
if (prepare_zap_oldest_mmu_page(kvm, &invalid_list))
freed++;
kvm_mmu_commit_zap_page(kvm, &invalid_list);
freed = kvm_mmu_zap_oldest_mmu_pages(kvm, sc->nr_to_scan);
unlock:
spin_unlock(&kvm->mmu_lock);