On Fri, Apr 03, 2015 at 03:27:51PM +0800, Xiao Guangrong wrote:
>
>
>On 04/03/2015 02:09 PM, Wanpeng Li wrote:
>>There are two scenarios for the requirement of collapsing small sptes
>>into large sptes.
>>- dirty logging tracks sptes in 4k granularity, so large sptes are split,
>> the large sptes will be reallocated in the destination machine and the
>> guest in the source machine will be destroyed when live migration successfully.
>> However, the guest in the source machine will continue to run if live migration
>> fail due to some reasons, the sptes still keep small which lead to bad
>> performance.
>>- our customers write tools to track the dirty speed of guests by EPT D bit/PML
>> in order to determine the most appropriate one to be live migrated, however
>> sptes will still keep small after tracking dirty speed.
>>
>>This patch introduce lazy collapse small sptes into large sptes, the memory region
>>will be scanned on the ioctl context when dirty log is stopped, the ones which can
>>be collapsed into large pages will be dropped during the scan, it depends the on
>>later #PF to reallocate all large sptes.
>>
>>Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
>>---
>>v1 -> v2:
>> * use 'bool' instead of 'int'
>> * add more comments
>> * fix can not get the next spte after drop the current spte
>>
>> arch/x86/include/asm/kvm_host.h | 2 ++
>> arch/x86/kvm/mmu.c | 71 +++++++++++++++++++++++++++++++++++++++++
>> arch/x86/kvm/x86.c | 19 +++++++++++
>> 3 files changed, 92 insertions(+)
>>
>>diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>>index 30b28dc..91b5bdb 100644
>>--- a/arch/x86/include/asm/kvm_host.h
>>+++ b/arch/x86/include/asm/kvm_host.h
>>@@ -854,6 +854,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
>> void kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
>> void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
>> struct kvm_memory_slot *memslot);
>>+void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
>>+ struct kvm_memory_slot *memslot);
>> void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm,
>> struct kvm_memory_slot *memslot);
>> void kvm_mmu_slot_largepage_remove_write_access(struct kvm *kvm,
>>diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>>index cee7592..df3f2e3 100644
>>--- a/arch/x86/kvm/mmu.c
>>+++ b/arch/x86/kvm/mmu.c
>>@@ -4465,6 +4465,77 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
>> kvm_flush_remote_tlbs(kvm);
>> }
>>
>>+static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
>>+ unsigned long *rmapp)
>>+{
>>+ u64 *sptep;
>>+ struct rmap_iterator iter;
>>+ int need_tlb_flush = 0;
>>+ pfn_t pfn;
>>+ struct kvm_mmu_page *sp;
>>+
>>+ while ((sptep = rmap_get_first(*rmapp, &iter))) {
>>+ BUG_ON(!(*sptep & PT_PRESENT_MASK));
>>+
>>+ sp = page_header(__pa(sptep));
>>+ pfn = spte_to_pfn(*sptep);
>>+
>>+ /*
>>+ * Let support EPT only now, an efficient way need to be figure
>>+ * out to let these code be aware what mapping level used in
>>+ * guest.
>
>This English seems strange... but i am not good at it. :)
I'm also not good at English, anyway, update it in v3. :)
>
>>+ */
>>+ if (sp->role.direct &&
>>+ !kvm_is_reserved_pfn(pfn) &&
>>+ PageTransCompound(pfn_to_page(pfn))) {
>>+ drop_spte(kvm, sptep);
>>+ need_tlb_flush = 1;
>>+ }
>
>If the conditions are not comfortable, it does loop forever...
Fix it in v3.
>
>Otherwise, it looks good to me.
>
>Reviewed-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
Thanks for your review. :)
Regards,
Wanpeng Li
>
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