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Re: [Xen-devel] [PATCH] Do not set page's count_info directly

Jiang, Yunhong wrote:
Keir Fraser <mailto:keir.fraser@xxxxxxxxxxxxx> wrote:
On 05/03/2009 12:45, "Gianluca Guida" <glguida@xxxxxxxxx> wrote:

On Thu, Mar 5, 2009 at 1:38 PM, Tim Deegan
<Tim.Deegan@xxxxxxxxxx> wrote:
The check doesn't tell you it's a shadow page -- it just tells you it's
*not* allocated in another way.  Checking with the mask is OK here,
perhaps with a comment change.
Yes, but this is what the code (in the shadow code) intends to check.
My complete plan is to have this macro and restore the idea of having
a flag for shadow pages because, as for now, the fact that we can't
distinguish clearly a shadow page should be considered a sort of bug,
given the code assumptions. Or at least a good basis for future bugs.
I'm happy for shadow code to have another bit in count_info
for its own use.
I don't think it's good to have other code (e.g., generic page offlining
code) peeking at it, is all. The particular case for a new
flag described
above sounds fine.

The new code is not using that flag anymore, it is use the 
page_get_owner_and_reference() to get the owner.

Yes, I was actually thinking about adding it. Turns out that I realized that it's not the best way to do stuff, but I think that I'll do the following:

- add a sh_page_is_a_shadow_page() in shadow code to make the code less confusing (with a small caveat comment about not being perfectly precise). - exercise my English skills by writing a comment in page_info that summarizes this thread findings about current use if count_info and shadow pages.


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