[Intel-gfx] [PATCH v9 5/8] drm/i915: add some kernel-doc for shrink_pin and friends

Matthew Auld
2021-10-18T09:12:14Z

Attempt to document shrink_pin and the other relevant interfaces that
interact with it, before we start messing with it.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
.../gpu/drm/i915/gem/i915_gem_object_types.h | 24 +++++++++++++-
drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 31 +++++++++++++++++++
2 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
index 7dd5f804aab3..f4233c4e8d2e 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
@@ -461,6 +461,28 @@ struct drm_i915_gem_object {
* instead go through the pin/unpin interfaces.
*/
atomic_t pages_pin_count;
+
+ /**
+ * @shrink_pin: Prevents the pages from being made visible to
+ * the shrinker, while the shrink_pin is non-zero. Most users
+ * should pretty much never have to care about this, outside of
+ * some special use cases.
+ *
+ * By default most objects will start out as visible to the
+ * shrinker(if I915_GEM_OBJECT_IS_SHRINKABLE) as soon as the
+ * backing pages are attached to the object, like in
+ * __i915_gem_object_set_pages(). They will then be removed the
+ * shrinker list once the pages are released.
+ *
+ * The @shrink_pin is incremented by calling
+ * i915_gem_object_make_unshrinkable(), which will also remove
+ * the object from the shrinker list, if the pin count was zero.
+ *
+ * Callers will then typically call
+ * i915_gem_object_make_shrinkable() or
+ * i915_gem_object_make_purgeable() to decrement the pin count,
+ * and make the pages visible again.
+ */
atomic_t shrink_pin;

/**
@@ -522,7 +544,7 @@ struct drm_i915_gem_object {
struct i915_gem_object_page_iter get_dma_page;

/**
- * Element within i915->mm.unbound_list or i915->mm.bound_list,
+ * Element within i915->mm.shrink_list or i915->mm.purge_list,
* locked by i915->mm.obj_lock.
*/
struct list_head link;
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
index ae2a8d54b7a4..66121fedc655 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
@@ -463,6 +463,16 @@ void i915_gem_shrinker_taints_mutex(struct drm_i915_private *i915,

#define obj_to_i915(obj__) to_i915((obj__)->base.dev)

+/**
+ * i915_gem_object_make_unshrinkable - Hide the object from the shrinker. By
+ * default all object types that support shrinking(see IS_SHRINKABLE), will also
+ * make the object visible to the shrinker after allocating the system memory
+ * pages.
+ * @obj: The GEM object.
+ *
+ * This is typically used for special kernel internal objects that can't be
+ * easily processed by the shrinker, like if they are perma-pinned.
+ */
void i915_gem_object_make_unshrinkable(struct drm_i915_gem_object *obj)
{
struct drm_i915_private *i915 = obj_to_i915(obj);
@@ -513,12 +523,33 @@ static void __i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj,
spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
}

+/**
+ * i915_gem_object_make_shrinkable - Move the object to the tail of the
+ * shrinkable list. Objects on this list might be swapped out. Used with
+ * WILLNEED objects.
+ * @obj: The GEM object.
+ *
+ * MUST only be called on objects which have backing pages.
+ *
+ * MUST be balanced with previous call to i915_gem_object_make_unshrinkable().
+ */
void i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj)
{
__i915_gem_object_make_shrinkable(obj,
&obj_to_i915(obj)->mm.shrink_list);
}

+/**
+ * i915_gem_object_make_purgeable - Move the object to the tail of the purgeable
+ * list. Used with DONTNEED objects. Unlike with shrinkable objects, the
+ * shrinker will attempt to discard the backing pages, instead of trying to swap
+ * them out.
+ * @obj: The GEM object.
+ *
+ * MUST only be called on objects which have backing pages.
+ *
+ * MUST be balanced with previous call to i915_gem_object_make_unshrinkable().
+ */
void i915_gem_object_make_purgeable(struct drm_i915_gem_object *obj)
{
__i915_gem_object_make_shrinkable(obj,
--
2.26.3