Re: [PATCH 11/11] KVM: MMU: improve write flooding detected

Marcelo Tosatti
2011-08-26T10:53:56Z

On Fri, Aug 26, 2011 at 11:18:01AM +0800, Xiao Guangrong wrote:
> On 08/25/2011 09:47 PM, Marcelo Tosatti wrote:
>
> > I guess it is OK to be more trigger happy with zapping by ignoring
> > the accessed bit, clearing the flood counter on page fault.
> >
>
> Yeah, i like this way, is this patch good for you?

Looks fine, can you rerun kernbench?

> ================================
> Subject: [PATCH 11/11] KVM: MMU: improve write flooding detected
>
> Detecting write-flooding does not work well, when we handle page written, if
> the last speculative spte is not accessed, we treat the page is
> write-flooding, however, we can speculative spte on many path, such as pte
> prefetch, page synced, that means the last speculative spte may be not point
> to the written page and the written page can be accessed via other sptes, so
> depends on the Accessed bit of the last speculative spte is not enough
>
> Instead of detected page accessed, we can detect whether the spte is accessed
> after it is written, if the spte is not accessed but it is written frequently,
> we treat is not a page table or it not used for a long time
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>