drm/i915: Report all objects with allocated pages to the shrinker

Currently, we try to report to the shrinker the precise number of
objects (pages) that are available to be reaped at this moment. This
requires searching all objects with allocated pages to see if they
fulfill the search criteria, and this count is performed quite
frequently. (The shrinker tries to free ~128 pages on each invocation,
before which we count all the objects; counting takes longer than
unbinding the objects!) If we take the pragmatic view that with
sufficient desire, all objects are eventually reapable (they become
inactive, or no longer used as framebuffer etc), we can simply return
the count of pinned pages maintained during get_pages/put_pages rather
than walk the lists every time.

The downside is that we may (slightly) over-report the number of
objects/pages we could shrink and so penalize ourselves by shrinking
more than required. This is mitigated by keeping the order in which we
shrink objects such that we avoid penalizing active and frequently used
objects, and if memory is so tight that we need to free them we would
need to anyway.

v2: Only expose shrinkable objects to the shrinker; a small reduction in
not considering stolen and foreign objects.
v3: Restore the tracking from a "backup" copy from before the gem/ split

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190530203500.26272-2-chris@chris-wilson.co.uk

1 files changed, 6 insertions, 22 deletions

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
index 6a93e326abf3..d71e630c6fb8 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
@@ -309,30 +309,14 @@ i915_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 {
 	struct drm_i915_private *i915 =
 		container_of(shrinker, struct drm_i915_private, mm.shrinker);
-	struct drm_i915_gem_object *obj;
-	unsigned long num_objects = 0;
-	unsigned long count = 0;
+	unsigned long num_objects;
+	unsigned long count;
 
-	spin_lock(&i915->mm.obj_lock);
-	list_for_each_entry(obj, &i915->mm.unbound_list, mm.link)
-		if (can_release_pages(obj)) {
-			count += obj->base.size >> PAGE_SHIFT;
-			num_objects++;
-		}
+	count = READ_ONCE(i915->mm.shrink_memory) >> PAGE_SHIFT;
+	num_objects = READ_ONCE(i915->mm.shrink_count);
 
-	list_for_each_entry(obj, &i915->mm.bound_list, mm.link)
-		if (!i915_gem_object_is_active(obj) && can_release_pages(obj)) {
-			count += obj->base.size >> PAGE_SHIFT;
-			num_objects++;
-		}
-	list_for_each_entry(obj, &i915->mm.purge_list, mm.link)
-		if (!i915_gem_object_is_active(obj) && can_release_pages(obj)) {
-			count += obj->base.size >> PAGE_SHIFT;
-			num_objects++;
-		}
-	spin_unlock(&i915->mm.obj_lock);
-
-	/* Update our preferred vmscan batch size for the next pass.
+	/*
+	 * Update our preferred vmscan batch size for the next pass.
 	 * Our rough guess for an effective batch size is roughly 2
 	 * available GEM objects worth of pages. That is we don't want
 	 * the shrinker to fire, until it is worth the cost of freeing an