On 17/12/15 14:26, Chris Wilson wrote:
On Thu, Dec 17, 2015 at 02:15:52PM +0000, Tvrtko Ursulin wrote:
+static void i915_ppgtt_close(struct i915_address_space *vm)
+{
+ struct list_head *phases[] = {
+ &vm->active_list,
+ &vm->inactive_list,
+ &vm->unbound_list,
+ NULL,
+ }, **phase;
+
+ RQ_BUG_ON(vm->is_ggtt);
+ RQ_BUG_ON(vm->closed);
+ vm->closed = true;
+
+ for (phase = phases; *phase; phase++) {
+ struct i915_vma *vma, *vn;
+
+ list_for_each_entry_safe(vma, vn, *phase, vm_link)
+ i915_vma_close(vma);
+ }
+}
Hm so VMAs get unlinked from everywhere, but then on retire goes
back to inactive. Is it not a bit weird?
Very weird. In the end, I have to stop unlinking in i915_vma_close()
from the vm lists.
Why it is needed to unlink VMAs from everywhere when marking them as closed?
Indeed, it was just to try and keep this walk short. But I realised that
this would actually also foul up the evict/shrinker (by hiding objects
from them that should be thrown away).
And actually on retire objects are ahead of VMAs in the
req->active_list so the last object unreference happens before the
last vma is retired, which is even weirder.
Am I missing something?
That shouldn't happen. The i915_gem_object_retire_read is run after the
i915_vma_retire.
I had added some commentary to i915_vma_move_to_active() that hopefully
explains the interdependences between retire callbacks (mostly to try
and prevent breakage later).
@@ -1075,7 +1075,13 @@ void i915_vma_move_to_active(struct i915_vma *vma,
obj->dirty = 1; /* be paranoid */
- /* Add a reference if we're newly entering the active list. */
+ /* Add a reference if we're newly entering the active list.
+ * The order in which we add operations to the retirement queue is
+ * vital here: mark_active adds to the start of the callback list,
+ * such that subsequent callbacks are called first. Therefore we
+ * add the active reference first and queue for it to be dropped
+ * *last*.
+ */
I don't know how I concluded active VMA is after the active object, and
I specifically saw the order and list_move.
Again, very good to document that, so something good at least came out
of it. :)
Regards,
Tvrtko
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