ring_buffer: allocate buffer page pointer

ring_buffer: allocate buffer page pointer

The current method of overlaying the page frame as the buffer page pointer
can be very dangerous and limits our ability to do other things with
a page from the buffer, like send it off to disk.

This patch allocates the buffer_page instead of overlaying the page's
page frame. The use of the buffer_page has hardly changed due to this.

Signed-off-by: Steven Rostedt <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>