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Re: Introducing non-RAM managed page ("device page")
On Tue, Sep 15, 2009 at 04:55:50PM +0000, Eduardo Horvath wrote:
> 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?
Yes. E.g. if you have a statically linked binary like /rescue/*, it
avoids buffering for 4MB or so :)
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