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Re: [Xen-devel] Re: [PATCH]Add a flag for shadow pages

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?


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