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 <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> ---
> 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.
> 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?
Paolo
> int write_flooding_count;
> };
>
>
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