Re: get_page_map in 2.2 vs 2.4

["Stephen C. Tweedie" <sct@redhat.com>]

Hi,

On Fri, Jun 30, 2000 at 12:38:19PM -0500, Timur Tabi wrote:
> 
> In 2.4, it's been changed to this:
> 
> /* 
>  * Given a physical address, is there a useful struct page pointing to
>  * it?  This may become more complex in the future if we start dealing
>  * with IO-aperture pages in kiobufs.
>  */
> 
> static inline struct page * get_page_map(struct page *page)
> {
> 	if (page > (mem_map + max_mapnr))
> 		return 0;
> 	return page;
> }

Yes.  get_page_map() takes a "struct page *" which has been obtained
through some magic pointer arithmetic; we still have to do the bounds
checking to make sure that the resulting pointer pointed to a valid
part of the mem_map array.  The comment about IO aperture memory still
stands, as in the future we may want to support the creation of
additional mem_map arrays at run time to map struct page *'s beyond
the end of physical memory, to allow kiobuf I/O on things like
framebuffers.

> Am I missing something?  What was wrong with the original implementation?

It didn't work on IA32 systems with >=1GB memory.

Cheers,
 Stephen
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