[Intel-gfx] [PATCH] drm/i915: Trim partial view sg lists

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Partial views are small but there can be many of them, and since the sg
list space for them is allocated pessimistically, we can save some slab by
trimming the unused tail entries.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
On the other hand with the diminishing importance of mmap ggtt do we
expect to see partial views in use these days?
---
 drivers/gpu/drm/i915/i915_drv.h     | 2 ++
 drivers/gpu/drm/i915/i915_gem.c     | 2 +-
 drivers/gpu/drm/i915/i915_gem_gtt.c | 2 ++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 8624b4bdc242..0fe22263aa9b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2323,6 +2323,8 @@ static inline struct scatterlist *__sg_next(struct scatterlist *sg)
 	     (((__iter).curr += PAGE_SIZE) >= (__iter).max) ?		\
 	     (__iter) = __sgt_iter(__sg_next((__iter).sgp), false), 0 : 0)
 
+bool i915_sg_trim(struct sg_table *orig_st);
+
 static inline unsigned int i915_sg_page_sizes(struct scatterlist *sg)
 {
 	unsigned int page_sizes;
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index db9688d14912..7156ddef178b 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2491,7 +2491,7 @@ void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
 	mutex_unlock(&obj->mm.lock);
 }
 
-static bool i915_sg_trim(struct sg_table *orig_st)
+bool i915_sg_trim(struct sg_table *orig_st)
 {
 	struct sg_table new_st;
 	struct scatterlist *sg, *new_sg;
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index f6c7ab413081..1ec721c20581 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -3835,6 +3835,8 @@ intel_partial_pages(const struct i915_ggtt_view *view,
 		count -= len >> PAGE_SHIFT;
 		if (count == 0) {
 			sg_mark_end(sg);
+			i915_sg_trim(st); /* Drop any unused tail entries. */
+
 			return st;
 		}
 
-- 
2.17.1