drm/i915/gem: Optimistically prune dma-resv from the shrinker.

As we shrink an object, also see if we can prune the dma-resv of idle
fences it is maintaining a reference to.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201223122051.4624-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/Makefile

@@ -58,6 +58,7 @@ i915-y += i915_drv.o \
 
 # core library code
 i915-y += \
+	dma_resv_utils.o \
 	i915_memcpy.o \
 	i915_mm.o \
 	i915_sw_fence.o \

drivers/gpu/drm/i915/dma_resv_utils.c

+// SPDX-License-Identifier: MIT
+/*
+ * Copyright © 2020 Intel Corporation
+ */
+
+#include <linux/dma-resv.h>
+
+#include "dma_resv_utils.h"
+
+void dma_resv_prune(struct dma_resv *resv)
+{
+	if (dma_resv_trylock(resv)) {
+		if (dma_resv_test_signaled_rcu(resv, true))
+			dma_resv_add_excl_fence(resv, NULL);
+		dma_resv_unlock(resv);
+	}
+}

drivers/gpu/drm/i915/dma_resv_utils.h

+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2020 Intel Corporation
+ */
+
+#ifndef DMA_RESV_UTILS_H
+#define DMA_RESV_UTILS_H
+
+struct dma_resv;
+
+void dma_resv_prune(struct dma_resv *resv);
+
+#endif /* DMA_RESV_UTILS_H */

drivers/gpu/drm/i915/gem/i915_gem_shrinker.c

@@ -15,6 +15,7 @@
 
 #include "gt/intel_gt_requests.h"
 
+#include "dma_resv_utils.h"
 #include "i915_trace.h"
 
 static bool swap_available(void)
@@ -209,6 +210,8 @@ i915_gem_shrink(struct drm_i915_private *i915,
 				mutex_unlock(&obj->mm.lock);
 			}
 
+			dma_resv_prune(obj->base.resv);
+
 			scanned += obj->base.size >> PAGE_SHIFT;
 			i915_gem_object_put(obj);
 

drivers/gpu/drm/i915/gem/i915_gem_wait.c

@@ -9,6 +9,7 @@
 
 #include "gt/intel_engine.h"
 
+#include "dma_resv_utils.h"
 #include "i915_gem_ioctls.h"
 #include "i915_gem_object.h"
 
@@ -84,11 +85,8 @@ i915_gem_object_wait_reservation(struct dma_resv *resv,
 	 * Opportunistically prune the fences iff we know they have *all* been
 	 * signaled.
 	 */
-	if (prune_fences && dma_resv_trylock(resv)) {
-		if (dma_resv_test_signaled_rcu(resv, true))
-			dma_resv_add_excl_fence(resv, NULL);
-		dma_resv_unlock(resv);
-	}
+	if (prune_fences)
+		dma_resv_prune(resv);
 
 	return timeout;
 }