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

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

This is mainly for page offline. When we offline a page, we we need turn to the 
caller the page's owner but we can't distinguish easily if it is a assigned 
page or a shadow page.

Thanks
Yunhong Jiang

Keir Fraser <mailto:keir.fraser@xxxxxxxxxxxxx> wrote:
> On 04/03/2009 08:46, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:
> 
>> Currently we don't know that a page is a shadow page unless we are in
>> shadow handler. This cause error when we try to get the page owner for the
>> shadow page, this snippet add a flag to it.
>> 
>> signed-off-by: Jiang, Yunhong <yunhong.jiang@xxxxxxxxx>
> 
> You only actually use your new flag in a BUG_ON, where it
> might avoid false
> negatives but hardly looks essential. Your other changes limit count_info
> checks to PGC_page_table|PGC_count_info which might be an
> improvement (I'm
> sure Tim or Gianluca can say) but they're existing fields.
> 
>> I'm not quite sure if the sh_put_ref() and
> sh_rm_write_access_from_sl1p() is
>> try to checking a page is shadow page (I assume so), because when a
>> anonymous page is allocated, the count_info is also 0 (like HVM's vlapic
>> page), so I change it like this patch (checking PGC_count_mask is 0).
>> Since comments in sh_hash_audit_bucket() has stated clearly it is to check
>> if it is shdow, so I replace it with test_bit(). 
>> 
>> Also, do we need checking in page_get_owner() also?
> 
> Usually gets used where we already get_page()ed or are about
> to get_page().
> Most Xen code knows that page uses can change under its feet
> unless it grabs
> a reference. So extra checks in page_get_owner() are probably rather
> pointless. 
> 
> -- Keir
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel