[PATCH 9/9] drm/i915: Trim struct_mutex hold duration for i915_gem_free_objects

Chris Wilson
2017-10-13T20:26:45Z

We free objects in bulk after they wait for their RCU grace period.
Currently, we take struct_mutex and unbind all the objects. This can lead
to a long lock duration during which time those objects have their pages
unfreeable (i.e. the shrinker is prevented from reaping those pages). If
we only process a single object under the struct_mutex and then free the
pages, the number of objects locked away from the shrinker is minimal
and we allow regular clients better access to struct_mutex if they need
it.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
drivers/gpu/drm/i915/i915_gem.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 2c92048a00fc..86dbf3af5a04 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4492,13 +4492,14 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
{
struct drm_i915_gem_object *obj, *on;

- mutex_lock(&i915->drm.struct_mutex);
intel_runtime_pm_get(i915);
- llist_for_each_entry(obj, freed, freed) {
+ llist_for_each_entry_safe(obj, on, freed, freed) {
struct i915_vma *vma, *vn;

trace_i915_gem_object_destroy(obj);

+ mutex_lock(&i915->drm.struct_mutex);
+
GEM_BUG_ON(i915_gem_object_is_active(obj));
list_for_each_entry_safe(vma, vn,
&obj->vma_list, obj_link) {
@@ -4521,13 +4522,8 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
spin_unlock(&i915->mm.obj_lock);
}

- }
- intel_runtime_pm_put(i915);
- mutex_unlock(&i915->drm.struct_mutex);
-
- cond_resched();
+ mutex_unlock(&i915->drm.struct_mutex);

- llist_for_each_entry_safe(obj, on, freed, freed) {
GEM_BUG_ON(obj->bind_count);
GEM_BUG_ON(obj->userfault_count);
GEM_BUG_ON(atomic_read(&obj->frontbuffer_bits));
@@ -4550,7 +4546,11 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,

kfree(obj->bit_17);
i915_gem_object_free(obj);
+
+ if (on)
+ cond_resched();
}
+ intel_runtime_pm_put(i915);
}

static void i915_gem_flush_free_objects(struct drm_i915_private *i915)