Zap at lease 10 pages before releasing mmu-lock to reduce the overload
caused by requiring lock
After the patch, kvm_zap_obsolete_pages can forward progress anyway,
so update the comments
[ It improves kernel building 0.6% ~ 1% ]
Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/mmu.c | 35 +++++++++++------------------------
1 files changed, 11 insertions(+), 24 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index f302540..688e755 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4203,14 +4203,18 @@ restart:
spin_unlock(&kvm->mmu_lock);
}
+#define BATCH_ZAP_PAGES 10
static void kvm_zap_obsolete_pages(struct kvm *kvm)
{
struct kvm_mmu_page *sp, *node;
LIST_HEAD(invalid_list);
+ int batch = 0;
restart:
list_for_each_entry_safe_reverse(sp, node,
&kvm->arch.active_mmu_pages, link) {
+ int ret;
+
/*
* No obsolete page exists before new created page since
* active_mmu_pages is the FIFO list.
@@ -4219,28 +4223,6 @@ restart:
break;
/*
- * Do not repeatedly zap a root page to avoid unnecessary
- * KVM_REQ_MMU_RELOAD, otherwise we may not be able to
- * progress:
- * vcpu 0 vcpu 1
- * call vcpu_enter_guest():
- * 1): handle KVM_REQ_MMU_RELOAD
- * and require mmu-lock to
- * load mmu
- * repeat:
- * 1): zap root page and
- * send KVM_REQ_MMU_RELOAD
- *
- * 2): if (cond_resched_lock(mmu-lock))
- *
- * 2): hold mmu-lock and load mmu
- *
- * 3): see KVM_REQ_MMU_RELOAD bit
- * on vcpu->requests is set
- * then return 1 to call
- * vcpu_enter_guest() again.
- * goto repeat;
- *
* Since we are reversely walking the list and the invalid
* list will be moved to the head, skip the invalid page
* can help us to avoid the infinity list walking.
@@ -4248,13 +4230,18 @@ restart:
if (sp->role.invalid)
continue;
- if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {
+ if (batch >= BATCH_ZAP_PAGES &&
+ (need_resched() || spin_needbreak(&kvm->mmu_lock))) {
+ batch = 0;
kvm_mmu_commit_zap_page(kvm, &invalid_list);
cond_resched_lock(&kvm->mmu_lock);
goto restart;
}
- if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list))
+ ret = kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list);
+ batch += ret;
+
+ if (ret)
goto restart;
}
--
1.7.7.6
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