dynamic VMALLOC_END, was Re: [PATCH 1/3] ARM: CSR: Adding CSR SiRFprimaII board support

[Nicolas Pitre]

On Fri, 8 Jul 2011, Arnd Bergmann wrote:

> On Friday 08 July 2011 20:09:29 Nicolas Pitre wrote:
> > Indeed.  The VMALLOC_END case is possibly different as we were trying to 
> > find a way to adjust it automatically at run time which would be one 
> > thing less for platforms to care about.  Having a globally fixed value 
> > for it would also solve the multiple definition problem.  But some 
> > machines have a large set of IO mappings while some others have a 
> > small one, so having a one size fits all solution here might be 
> > suboptimal.
> 
> Is everything between VMALLOC_END and 0xfeffffff guaranteed to come
> from iotable_init? If so, we could perhaps turn it into a variable
> that gets initialized to 0xfeffffff and decreased by iotable_init
> to be just below the lowest address that has actually been mapped.
> 
> Obviously, anything that derives values from VMALLOC_END at compile
> time would need to change, too.

You then have a catch22 situation, because one thing that gets derived 
from VMALLOC_END is the highmem threshold, and that has to be determined 
before iotable_init can be used.  And having a fixed highmem threshold 
is not any better than a globally fixed VMALLOC_END of course.


Nicolas