From: Zhuang Yanying <ann.zhuangyanying@xxxxxxxxxx> Recently I tested live-migration with large-memory guests, find vcpu may hang for a long time while starting migration, such as 9s for 2048G(linux-5.0.0-rc2+qemu-3.1.0). The reason is memory_global_dirty_log_start() taking too long, and the vcpu is waiting for BQL. The page-by-page D bit clearup is the main time consumption. I think that the idea of "KVM: MMU: fast write protect" by xiaoguangrong, especially the function kvm_mmu_write_protect_all_pages(), is very helpful. After a little modifcation, on his patch, can solve this problem, 9s to 0.5s. At the begining of live migration, write protection is only applied to the top-level SPTE. Then the write from vm trigger the EPT violation, with for_each_shadow_entry write protection is performed at dirct_map. Finally the Dirty bit of the target page(at level 1 page table) is cleared, and the dirty page tracking is started. Of coure, the page where GPA is located is marked dirty when mmu_set_spte. A similar implementation on xen, just emt instead of write protection. What do you think about this solution? Xiao Guangrong (3): KVM: MMU: correct the behavior of mmu_spte_update_no_track KVM: MMU: introduce possible_writable_spte_bitmap KVM: MMU: introduce kvm_mmu_write_protect_all_pages Zhuang Yanying (1): KVM: MMU: fast cleanup D bit based on fast write protect arch/x86/include/asm/kvm_host.h | 25 +++- arch/x86/kvm/mmu.c | 259 ++++++++++++++++++++++++++++++++++++++-- arch/x86/kvm/mmu.h | 1 + arch/x86/kvm/paging_tmpl.h | 13 +- arch/x86/kvm/vmx/vmx.c | 3 +- 5 files changed, 286 insertions(+), 15 deletions(-) -- 1.8.3.1
