[Intel-gfx] [PATCH 1/3] drm/i915: Stop holding a ref to the ppgtt from each vma

[Chris Wilson]

Quoting Mika Kuoppala (2018-08-16 12:42:08)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > The context owns both the ppgtt and the vma within it, and our activity
> > tracking on the context ensures that we do not release active ppgtt. As
> > the context fulfils our obligations for active memory tracking, we can
> > relinquish the reference from the vma.
> >
> 
> The part of owning the vma within it escapes me. The vma is tied
> to the object. Is it about that active objects, with their vmas
> hold the refs to the context they are executing on?

The vma belongs to the (object, context). If the context is closed (or
on close(/dev/dri/card0)), so is the ppgtt. Closing the object
(gem_close(fd, obj)) closes the vma that match the contexts for the fd,
and if it was the last handle, then frees the object.
 
> > This fixes a silly transient refleak from closed vma being kept alive
> > until the entire system was idle, keeping all vm alive as well.
> >
> > Reported-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > Testcase: igt/gem_ctx_create/files
> > Fixes: 3365e2268b6b ("drm/i915: Lazily unbind vma on close")
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_vma.c | 4 ----
> >  1 file changed, 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> > index 274fd2a7bcb6..31efc971a3a8 100644
> > --- a/drivers/gpu/drm/i915/i915_vma.c
> > +++ b/drivers/gpu/drm/i915/i915_vma.c
> > @@ -199,7 +199,6 @@ vma_create(struct drm_i915_gem_object *obj,
> >               vma->flags |= I915_VMA_GGTT;
> >               list_add(&vma->obj_link, &obj->vma_list);
> >       } else {
> > -             i915_ppgtt_get(i915_vm_to_ppgtt(vm));
> 
> It seems this is the sole user of i915_ppgtt_get so you can
> remove that too.

Such shortsightedness; it will reappear shortly. See the patches to
share vm between contexts.
-Chris