[PATCH] drm/i915: Wait for the mutex whilst the reaper runs

[Chris Wilson <chris@chris-wilson.co.uk>]

If the system is forced to start kswapd to recover pages, the system is
very starved. Fortunately, kswapd is its own process context and can
wait for the mutex.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index ff2ea2b..7108493 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4600,8 +4600,16 @@ i915_gem_inactive_shrink(struct shrinker *shrinker, struct shrink_control *sc)
 	int nr_to_scan = sc->nr_to_scan;
 	int cnt;
 
-	if (!mutex_trylock(&dev->struct_mutex))
-		return 0;
+	/* Force reaping when kswapd runs and the system is starved of
+	 * free pages, Otherwise only opportunistically shrink our caches,
+	 * being wary of deadlocks.
+	 */
+	if (current_is_kswapd()) {
+		mutex_lock(&dev->struct_mutex);
+	} else {
+		if (!mutex_trylock(&dev->struct_mutex))
+			return 0;
+	}
 
 	if (nr_to_scan) {
 		nr_to_scan -= i915_gem_purge(dev_priv, nr_to_scan);
-- 
1.7.10.4