Re: Introducing non-RAM managed page ("device page")

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

On Tue, 15 Sep 2009, Joerg Sonnenberger wrote:

> On Tue, Sep 15, 2009 at 04:04:15PM +0000, Eduardo Horvath wrote:
> > We've handled mmap()ing device memory forever without getting VM involved.  
> > Not to imply that the current device mmap() interface could not be 
> > improved.  What features of the VM subsystem do you think is needed to map 
> > device pages into processes?
> 
> This is *not* mmap on a device. It is mmap of a file stored on a special
> device. In other words, read-only access to this device can be done
> without the buffer cache and for that the VM subsystem needs glue.

So the purpose of this excercise is to allow the buffer cache to use 
non-VM pages?  Nifty, but does the memory you gain by not needing buffer 
cache pages offset the additional code and control structures?

Eduardo