Re: [patch 0/4] add e500 platform support for KVM

[Hollis Blanchard <hollisb@us.ibm.com>]

On Monday 08 September 2008 21:08:02 Liu Yu-B13201 wrote:
> 
> > You can't assume that TLB1 does not contain user mappings, because
> > that's not true with hugetlbfs. Of course, hugetlbfs doesn't (yet?)
> > exist for e500, so the assumption is valid until that happens.
> > 
> > However, we *really* need large host page mappings to make KVM fast.
> > Right now we have to split guest large pages (covering the 
> > kernel) into
> > lots of 4K mappings, which means our TLB miss rate is *much* 
> > higher than
> > if we could use hugetlbfs on the host. In that case, we could use
> > hugetlbfs large user pages to back the guest kernel mappings.
> > 
> 
> Yes. It's a problem. But I afraid e500 would not use hugetlbfs,
> as it means to give up 512-entry TLB0, while TLB1 has only 16 entries.

I don't think you'd need to "give up" anything -- some parts of user memory 
would be backed with 4K pages, and some parts with large pages.

-- 
Hollis Blanchard
IBM Linux Technology Center