Re: Protecting global lookup array

[David Holland <dholland-tech%netbsd.org@localhost>]

On Mon, Feb 08, 2010 at 11:40:50AM +0900, Masao Uebayashi wrote:
 > I'm adding another list of vm_physseg for device pages.  It's a
 > list or array of physical address segments.  They're frequently
 > accessed by VM to lookup a physical address from a page metadata
 > (vm_page) or vice versa.
 > 
 > Those lists are rarely updated.  When a framebuffer or
 > memory-mappable audio device are attached / detached.  (For RAM
 > segments, they're updated when we'll support memory hot-plug. :)
 > 
 > The update process is very rare, and expected.  Administrators
 > carefully connects a device when the machine is not running some
 > important task.  So what I need here is to protect such a data
 > adding no run-time performance loss.

On the plus side, this is essentially the same problem as safely
switching vnodes to deadfs after a umount -f; on the minus side,
nobody's yet come up with a satisfactory solution for that...

-- 
David A. Holland
dholland%netbsd.org@localhost