drm/i915: Wait for the GPU whilst shrinking, if truly desperate.

By idling the GPU and discarding everything we can when under extreme
memory pressure, the number of OOM-killer events is dramatically
reduced. For instance, this makes it possible to run
firefox-planet-gnome.trace again on my swapless 512MiB i915.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>

1 files changed, 45 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 47c46ed384f1..3471dece13e7 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -5066,6 +5066,20 @@ void i915_gem_release(struct drm_device * dev, struct drm_file *file_priv)
 }
 
 static int
+i915_gpu_is_active(struct drm_device *dev)
+{
+        drm_i915_private_t *dev_priv = dev->dev_private;
+        int lists_empty;
+
+        spin_lock(&dev_priv->mm.active_list_lock);
+        lists_empty = list_empty(&dev_priv->mm.flushing_list) &&
+                      list_empty(&dev_priv->mm.active_list);
+        spin_unlock(&dev_priv->mm.active_list_lock);
+
+        return !lists_empty;
+}
+
+static int
 i915_gem_shrink(int nr_to_scan, gfp_t gfp_mask)
 {
         drm_i915_private_t *dev_priv, *next_dev;
@@ -5094,6 +5108,7 @@ i915_gem_shrink(int nr_to_scan, gfp_t gfp_mask)
 
         spin_lock(&shrink_list_lock);
 
+rescan:
         /* first scan for clean buffers */
         list_for_each_entry_safe(dev_priv, next_dev,
                                  &shrink_list, mm.shrink_list) {
@@ -5151,6 +5166,36 @@ i915_gem_shrink(int nr_to_scan, gfp_t gfp_mask)
                 would_deadlock = 0;
         }
 
+        if (nr_to_scan) {
+                int active = 0;
+
+                /*
+                 * We are desperate for pages, so as a last resort, wait
+                 * for the GPU to finish and discard whatever we can.
+                 * This has a dramatic impact to reduce the number of
+                 * OOM-killer events whilst running the GPU aggressively.
+                 */
+                list_for_each_entry(dev_priv, &shrink_list, mm.shrink_list) {
+                        struct drm_device *dev = dev_priv->dev;
+
+                        if (!mutex_trylock(&dev->struct_mutex))
+                                continue;
+
+                        spin_unlock(&shrink_list_lock);
+
+                        if (i915_gpu_is_active(dev)) {
+                                i915_gpu_idle(dev);
+                                active++;
+                        }
+
+                        spin_lock(&shrink_list_lock);
+                        mutex_unlock(&dev->struct_mutex);
+                }
+
+                if (active)
+                        goto rescan;
+        }
+
         spin_unlock(&shrink_list_lock);
 
         if (would_deadlock)