On 06/19/2013 07:58 PM, Paolo Bonzini wrote: > Il 19/06/2013 11:09, Xiao Guangrong ha scritto: >> Document write_flooding_count to Documentation/virtual/kvm/mmu.txt >> >> Signed-off-by: Xiao Guangrong <xiaoguangr...@linux.vnet.ibm.com> >> --- >> Documentation/virtual/kvm/mmu.txt | 8 ++++++++ >> arch/x86/include/asm/kvm_host.h | 5 +++++ >> 2 files changed, 13 insertions(+) >> >> diff --git a/Documentation/virtual/kvm/mmu.txt >> b/Documentation/virtual/kvm/mmu.txt >> index ce6df51..5a6b2e2 100644 >> --- a/Documentation/virtual/kvm/mmu.txt >> +++ b/Documentation/virtual/kvm/mmu.txt >> @@ -214,6 +214,14 @@ Shadow pages contain the following information: >> It is only used on 32bit host which helps us to detect whether updating >> the >> 64bit spte is complete so that we can avoid reading the truncated value >> out >> of mmu-lock. >> + write_flooding_count: >> + In order to sync the page table between guest and host, the page >> sometimes >> + needs to be write-protected (see "Synchronized and unsynchronized pages" >> + below), any write to the page can cause write emulation. If the >> emulation >> + on the page is too frequent we'd better unmap the page to avoid the >> + future emulation. write_flooding_count aims at this optimization which >> is >> + increased when the page needs to be write emulated and cleared when the >> + page is actually used. > > A guest may write to a page table many times, causing a lot of > emulations if the page needs to be write-protected (see "Synchronized > and unsynchronized pages" below). Leaf pages can be unsynchronized > so that they do not trigger frequent emulation, but this is not > possible for non-leafs. This field counts the number of emulations > since the last time the page table was actually used; if emulation > is triggered too frequently on this page, KVM will unmap the page > to avoid emulation in the future.
very nice. > >> Reverse map >> =========== >> diff --git a/arch/x86/include/asm/kvm_host.h >> b/arch/x86/include/asm/kvm_host.h >> index 1dac2c1..5eb5382 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -234,6 +234,11 @@ struct kvm_mmu_page { >> int clear_spte_count; >> #endif >> >> + /* >> + * Increased when the page needs to be write emulated, cleared >> + * when the page is actually used as page table to avoid frequent >> + * emulation on the page. >> + */ > > /* Number of writes since the last time traversal visited this page. > */ > > wdyt, better or worse? I think it is better. :) Thanks for your refining. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/