[Intel-gfx] [RFC 2/2] drm/i915: Clean-up PPGTT on context destruction

[Daniel Vetter]

On Thu, Feb 12, 2015 at 09:03:06PM +0000, Chris Wilson wrote:
> On Thu, Feb 12, 2015 at 08:05:02PM +0000, rafael.barbalho at intel.com wrote:
> > From: Rafael Barbalho <rafael.barbalho at intel.com>
> > 
> > With full PPGTT enabled an object's VMA entry into a PPGTT VM needs to be
> > cleaned up so that the PPGTT PDE & PTE allocations can be freed.
> > 
> > This problem only shows up with full PPGTT because an object's VMA is
> > only cleaned-up when the object is destroyed. However, if the object has
> > been shared between multiple processes this may not happen, which leads to
> > references to the PPGTT still being kept the object was shared.
> > 
> > Under android the sharing of GEM objects is a fairly common operation, thus
> > the clean-up has to be more agressive.
> 
> Not quite. You need an active refcount as we do not expect close(fd) to
> stall. The trick is to "simply" use requests to retire vma (as well as
> the object management it does today, though that just becomes a second
> layer for GEM API management, everything else goes through vma).

Linking into the ctx unref should give us that for free since requests do
hold a reference on the context. So this will only be run when the buffers
are idle.

Well except that our unbind code is too dense to do that correctly for
shared buffers, so we need to move obj->active to vma->active first.

And yeah the commit message should have explained this.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch