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

[Chris Wilson]

On Fri, Feb 13, 2015 at 10:55:46AM +0100, Daniel Vetter wrote:
> 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.

We unbind vma, so what do you mean?

This is how I forsee the code:

static int context_idr_cleanup(int id, void *p, void *data)
{
        struct intel_context *ctx = p;

        if (ctx->ppgtt && !i915_gem_context_is_default(ctx)) {
                struct list_head *list;
                struct i915_vma *vma;

                /* Decouple the remaining vma to keep the next lookup fast */
                list = &ctx->ppgtt->base.vma_list;
                while (!list_empty(list)) {
                        vma = list_first_entry(list, typeof(*vma), vm_link);
                        list_del_init(&vma->vm_link);
                        list_del_init(&vma->obj_link);
                        i915_vma_put(vma);
                }

                /* Drop active references to this vm upon retire */
                ctx->ppgtt->base.closed = true;

                /* Drop all inactive references (via vma->vm reference) */
                list = &ctx->ppgtt->base.inactive_list;
                while (!list_empty(list)) {
                        struct drm_i915_gem_object *obj;
                        int ret;

                        vma = list_first_entry(list, typeof(*vma), mm_list);
                        obj = vma->obj;

                        drm_gem_object_reference(&obj->base);
                        ret = i915_vma_unbind(vma);
                        drm_gem_object_unreference(&obj->base);
                        if (WARN_ON(ret))
                                break;
                }
        }

        ctx->file_priv = NULL;
        i915_gem_context_unreference(ctx);

        return 0;
}
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre