Re: [Xen-ia64-devel] RE: [Xen-devel] RE: Linux PG_arch_1 conflict

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Tue, Mar 14, 2006 at 10:54:05AM +0800, Tian, Kevin wrote:
> >From: Isaku Yamahata
> >Sent: 2006年3月14日 10:12
> >> > > Comments, Keir (or others)?
> >> >
> >> > Sounds like the proper fix. I'll leave it to Christian and others
> >> > involved in the Linux upstreaming effort to have the final word.
> >>
> >> Comments, Christian (or others)?  Any chance this will get into
> >> 3.0.2?  Certainly it should be changed before attempting to push
> >> the drivers upstream to Linux.
> >
> >What do you think of the followings? Too hacky?
> >
> >
> >extern struct address_space xen_ia64_foreign_dummy_mapping;
> >#define PageForeign(page)    \
> >     (page->mapping == &xen_ia64_foreign_dummy_mapping)
> >
> >#define SetPageForeign(page, dtor) do {                              \
> >     set_page_private((page), (unsigned long)dtor);          \
> >     (page)->mapping = &xen_ia64_foreign_dummy_mapping;      \
> >} while (0)
> >
> >#define ClearPageForeign(page) do {  \
> >     (page)->mapping = NULL;         \
> >     set_page_private((page), 0);    \
> >} while (0)
> >
> >#define PageForeignDestructor(page)  \
> >     ( (void (*) (struct page *)) page_private((page)) )
> >
> 
> Hi, Isaku,
>       (page)->mapping is used to keep special destructor since that foreign 
> page needs to be freed differently as normal linux pages, as you see in 
> foreign_page.h. Your hack only ensures the check. Agree right way to go to 
> propose PG_foreign upstream.

A special destructor is kept in page->private by set_page_private() and
get by page_private(). page->private is unsigned long so that it can
hold pointer value.

They are just defined as
#define page_private(page)              ((page)->private)
#define set_page_private(page, v)       ((page)->private = (v))



-- 
yamahata

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