Re: Re: [PATCH]Add a flag for shadow pages

[Gianluca Guida <gianluca.guida@eu.citrix.com>]

Jiang, Yunhong wrote:
> Thanks for your really quick-hand implementation. I will update my another patch accordingly tomorrow.
> 
> So still one question to the two assertion (or to Tim??) in sh_rm_write_access_from_sl1p()/sh_put_ref(). What's the potential error to be protected by this checking? If page is a shadow, it's count_info will always be 0, right? Or it is just a sanity checking?

They're sanity checking. Checks are there to be sure that the page is a 
shadow page. It used to be "->mbz == 0", which was clearer, in the old 
page_info model.

In the sh_rm_write_access_from_sl1p(), the check is there to ensure that 
the page is *still* a shadow page. As for current code, though, that 
check should be useless.

I actually think that having a more precise way of knowing when a page 
is a shadow page is definitely needed, for debugging or even in case the 
shadow allocation becomes more dynamic in the future.

> I need change this is because, if we mark a page offline, then the count_info is not 0, even for shadow page. Can I just checking the count_mask here?

Ehr, I am not following the discussions about your patch, but I suppose 
you set the page off-line after all references and uses of the page, 
even inside shadows, are removed. Or the count_info is != 0 to signal 
that the page is going offline?

Thanks,
Gianluca