Re: [Qemu-devel] Migration ToDo list

[Isaku Yamahata]

On Wed, Nov 14, 2012 at 03:20:08AM +0100, Paolo Bonzini wrote:
> Il 14/11/2012 03:14, Isaku Yamahata ha scritto:
> >> > Identifying ballooned zero pages is useful, because those cause the
> >> > clear_page calls in the kernel even in a guest that has been running for
> >> > a while.
> >> > 
> >> > But a generic solution doesn't really matter, because is_dup_page and
> >> > clear_page shouldn't really be in the profile in practice, except in
> >> > microbenchmarks.
> > I guess mincore(2) can be used as easy way to detect non-mapped page.
> > This is just implementation detail anyway.
> 
> Doesn't work if the page is swapped, doesn't it?

Ah, I meant if page is in memory, we can skip is_dup_page for that page.
Only check pages that is not-mapped or swapped.
If more detailed info is needed, /proc/<pid>/pagemap would be used.


> But I wonder if the clear_page occurrences are because of the problem
> described recently on LWN (http://lwn.net/Articles/517465/), and so
> really more of a kernel bug than anything else.
> 
> Paolo
> 

-- 
yamahata