[Intel-gfx] [RFC 3/5] drm/i915: Add support for CPU mapping to DRM_IOCTL_I915_GEM_MMAP_GTT

[Chris Wilson]

On Wed, Jan 27, 2016 at 03:24:43PM +0000, Tvrtko Ursulin wrote:
> 
> On 26/01/16 16:59, Chris Wilson wrote:
> >Another thing I realised was that this severely limits the mmap space on
> >32-bit systems, as the vma manager is unsigned long. The CPU mmaping was
> >a way around some of the restrictions. That would seem fairly easy to
> >lift (and I hope without consequence).
> 
> I did not manage to figure out what here limits the space on 32-bit systems?

A hang-over of mine. We once used to exhaust the 32bit mmap space quite
easily. I was thinking drm_vma_manager had the same limit due to its use
of unsigned long, but it is counting in pages not bytes, so we have
44bits available of space, which will hopefully be enuogh for the last
remaining 32bit system to grow old gracefully.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre