drm/i915: Trim partial view sg lists

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@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180926080353.20867-1-tvrtko.ursulin@linux.intel.com

3 files changed, 5 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9e185f0a822a..ab52657cc3d0 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2325,6 +2325,8 @@ 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 627b1c8a7ea3..28e943ee8b5e 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2491,7 +2491,7 @@ unlock:
         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;
                 }