Re: [Xen-devel] struct page_info

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

Jan Beulich wrote:
> > > > Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> 24.04.09 05:15 >>>
> > Now, looking at it, the shadow page is confusing.
> >
> >         /* Page is in use: ((count_info & PGC_count_mask) != 0).  */
> >         ..
> >
> >         /* Page is in use as a shadow: count_info == 0. */
> >         ..
> >         /* Page is on a free list: ((count_info & PGC_count_mask) == 0). */
> >         ..
> >
> > If count_info == 0, and it implies shadow page, how's that different
> > from an unallocated page which also would've count_info=0 I presume?
> These are not if-and-only-if conditions, so you can't conclude the use of
> a page from just looking at count_info; only the other way around: from
> e.g. knowing the page is in use as a shadow, you'll know count_info must
> be zero.
Ahh, so I found a mfn on the floor no easy way of knowing where it
belongs. Okey.

thanks
Mukesh



> > Also, if "Page is on a free list:", I assume one of the PGC_ fields would
> > be set?
> Not would, but might.
>
> Jan
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