Re: struct page_info

[Mukesh Rathor <mukesh.rathor@oracle.com>]

Jan Beulich wrote:
>>>> Mukesh Rathor <mukesh.rathor@oracle.com> 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