[Intel-gfx] [PATCH] drm/i915: Revert shrinker changes from "Track unbound pages"

[Daniel Vetter]

This partially reverts

commit 6c085a728cf000ac1865d66f8c9b52935558b328
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Mon Aug 20 11:40:46 2012 +0200

    drm/i915: Track unbound pages

Closer inspection of that patch revealed a bunch of unrelated changes
in the shrinker:
- The shrinker count is now in pages instead of objects.
- For counting the shrinkable objects the old code only looked at the
  inactive list, the new code looks at all bounds objects (including
  pinned ones). That is obviously in addition to the new unbound list.
- The shrinker cound is no longer scaled with
  sysctl_vfs_cache_pressure.
- When actually shrinking objects, the old code first dropped
  purgeable objects, then normal (inactive) objects. Only then did it,
  in a last-ditch effort idle the gpu and evict everything. The new
  code omits the intermediate step of evicting normal inactive
  objects.

Safe for the first change, which seems benign, the endresult of all
these changes is that the shrinker is _much_ more likely to fall back
to the last-ditch resort of idling the gpu and evicting everything.
The old code could only do that if something else evicted lots of
objects meanwhile (since without any other changes the nr_to_scan will
be smaller than the object count).

Hence revert all these changes and restore the old shrinker behaviour,
with the minor adjustment that we now first scan the unbound list,
then the inactive list for each object category (purgeable or normal).

A similar patch has been tested by a few people affected by the gen4/5
hangs which started to appear in 3.7, which some people bisected to
the "drm/i915: Track unbound pages" commit. But just disabling the
unbound logic alone didn't change things at all.

References: https://bugs.freedesktop.org/show_bug.cgi?id=55984
References: https://bugs.freedesktop.org/show_bug.cgi?id=57122
References: https://bugs.freedesktop.org/show_bug.cgi?id=56916
References: https://bugs.freedesktop.org/show_bug.cgi?id=57136
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: stable at vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/i915_gem.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 51df4ee..7c42788 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1714,7 +1714,8 @@ i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
 }
 
 static long
-i915_gem_purge(struct drm_i915_private *dev_priv, long target)
+__i915_gem_shrink(struct drm_i915_private *dev_priv, long target,
+		  bool purgeable_only)
 {
 	struct drm_i915_gem_object *obj, *next;
 	long count = 0;
@@ -1722,7 +1723,7 @@ i915_gem_purge(struct drm_i915_private *dev_priv, long target)
 	list_for_each_entry_safe(obj, next,
 				 &dev_priv->mm.unbound_list,
 				 gtt_list) {
-		if (i915_gem_object_is_purgeable(obj) &&
+		if ((i915_gem_object_is_purgeable(obj) || !purgeable_only) &&
 		    i915_gem_object_put_pages(obj) == 0) {
 			count += obj->base.size >> PAGE_SHIFT;
 			if (count >= target)
@@ -1733,7 +1734,7 @@ i915_gem_purge(struct drm_i915_private *dev_priv, long target)
 	list_for_each_entry_safe(obj, next,
 				 &dev_priv->mm.inactive_list,
 				 mm_list) {
-		if (i915_gem_object_is_purgeable(obj) &&
+		if ((i915_gem_object_is_purgeable(obj) || !purgeable_only) &&
 		    i915_gem_object_unbind(obj) == 0 &&
 		    i915_gem_object_put_pages(obj) == 0) {
 			count += obj->base.size >> PAGE_SHIFT;
@@ -1745,6 +1746,12 @@ i915_gem_purge(struct drm_i915_private *dev_priv, long target)
 	return count;
 }
 
+static long
+i915_gem_purge(struct drm_i915_private *dev_priv, long target)
+{
+	return __i915_gem_shrink(dev_priv, target, true);
+}
+
 static void
 i915_gem_shrink_all(struct drm_i915_private *dev_priv)
 {
@@ -4415,6 +4422,9 @@ i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
 	if (nr_to_scan) {
 		nr_to_scan -= i915_gem_purge(dev_priv, nr_to_scan);
 		if (nr_to_scan > 0)
+			nr_to_scan -= __i915_gem_shrink(dev_priv, nr_to_scan,
+							false);
+		if (nr_to_scan > 0)
 			i915_gem_shrink_all(dev_priv);
 	}
 
@@ -4422,11 +4432,11 @@ i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
 	list_for_each_entry(obj, &dev_priv->mm.unbound_list, gtt_list)
 		if (obj->pages_pin_count == 0)
 			cnt += obj->base.size >> PAGE_SHIFT;
-	list_for_each_entry(obj, &dev_priv->mm.bound_list, gtt_list)
+	list_for_each_entry(obj, &dev_priv->mm.inactive_list, gtt_list)
 		if (obj->pin_count == 0 && obj->pages_pin_count == 0)
 			cnt += obj->base.size >> PAGE_SHIFT;
 
 	if (unlock)
 		mutex_unlock(&dev->struct_mutex);
-	return cnt;
+	return cnt / 100 * sysctl_vfs_cache_pressure;
 }
-- 
1.7.11.7