[PATCH 12/87] drm/i915: Drain freed objects for mmap space exhaustion

Chris Wilson chris at chris-wilson.co.uk
Fri Jan 6 12:24:51 UTC 2017


On Fri, Jan 06, 2017 at 12:06:30PM +0000, Tvrtko Ursulin wrote:
> 
> On 05/01/2017 23:19, Chris Wilson wrote:
> >As we now use a deferred free queue for objects, simply retiring the
> >active objects is not enough to immediately free them and recover their
> >mmap space - we must now also drain the freed object list.
> >
> >Fixes: fbbd37b36fa5 ("drm/i915: Move object release to a freelist + worker"
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> >Cc: <drm-intel-fixes at lists.freedesktop.org>
> >---
> > drivers/gpu/drm/i915/i915_gem.c | 24 +++++++++++-------------
> > 1 file changed, 11 insertions(+), 13 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> >index c8bc2cd9d479..d2ca6f729f42 100644
> >--- a/drivers/gpu/drm/i915/i915_gem.c
> >+++ b/drivers/gpu/drm/i915/i915_gem.c
> >@@ -2090,23 +2090,21 @@ static int i915_gem_object_create_mmap_offset(struct drm_i915_gem_object *obj)
> > 	int err;
> >
> > 	err = drm_gem_create_mmap_offset(&obj->base);
> >-	if (!err)
> >+	if (likely(!err))
> > 		return 0;
> >
> >-	/* We can idle the GPU locklessly to flush stale objects, but in order
> >-	 * to claim that space for ourselves, we need to take the big
> >-	 * struct_mutex to free the requests+objects and allocate our slot.
> >-	 */
> >-	err = i915_gem_wait_for_idle(dev_priv, I915_WAIT_INTERRUPTIBLE);
> >-	if (err)
> >-		return err;
> >+	/* Attempt to reap some mmap space from dead objects */
> >+	do {
> >+		err = i915_gem_wait_for_idle(dev_priv, I915_WAIT_INTERRUPTIBLE);
> >+		if (err)
> >+			break;
> >
> >-	err = i915_mutex_lock_interruptible(&dev_priv->drm);
> >-	if (!err) {
> >-		i915_gem_retire_requests(dev_priv);
> >+		i915_gem_drain_freed_objects(dev_priv);
> > 		err = drm_gem_create_mmap_offset(&obj->base);
> >-		mutex_unlock(&dev_priv->drm.struct_mutex);
> >-	}
> >+		if (!err)
> >+			break;
> >+
> >+	} while (flush_delayed_work(&dev_priv->gt.retire_work));
> >
> > 	return err;
> > }
> >
> 
> Hmm.. what about the shrinker and for example the patch I just
> reviewed - "drm/i915: Purge loose pages if we run out of DMA remap
> space" - we would need the same strategy there, no? Maybe move this
> logic to a helper like ..._retire_and_free ?

... so the shrinker digs around underneath and does exactly what the
work would do but immediately.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre


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