Maximum bootable kernel size in current ARM linux

[Nicolas Pitre]

On Thu, 16 Sep 2010, Catalin Marinas wrote:

> On Tue, 2010-09-14 at 13:37 -0400, Nicolas Pitre wrote:
> > On Tue, 14 Sep 2010, Catalin Marinas wrote:
> > 
> > > I think the Thumb-2 branch goes up to 16MB range. The Thumb-1 may be
> > > smaller but we don't support this in the kernel. That's why Thumb-2
> > > modules are within 8MB below PAGE_OFFSET. But this leaves us with
> > > maximum 8MB of kernel size.
> > 
> > Hmmm.  Would be worth moving the pkmap area below modules then.
> 
> So currently the pkmap area is at PAGE_OFFSET - 2MB. On a Thumb-2 kernel
> with highmem enabled we would have 6MB available to modules. Is this big
> enough? If not, we could move the pkmap area.

It is probably enough. But it is just not optimal.  If the area between 
TASK_SIZE and PAGE_OFFSET-8M is unused, then it would make sense to move 
the pkmap area there instead.

> BTW, can it be moved in the top part of the memory rather than below
> PAGE_OFFSET?

It could, but top memory layout tend to be machine specific, or already 
used by the consistent DMA.  And the module area is underused anyway.


Nicolas