drm/v3d: Only use Big/Super Pages if BO >= 512KB

Considering that the Raspberry Pi is an embedded device with limited
memory, memory fragmentation is an important aspect for performance.
Using Big/Super Pages has clear benefits when it comes to reducing TLB
misses, but also has an impact on memory fragmentation as we need to
allocate aligned contiguous memory, increasing compaction pressure and
memory waste for small BOs.

As Big/Super Pages only have benefits for larger BOs, create a minimum
BO size to use the THP partition. After testing different thresholds,
512KB provides the most balanced results with clear improvements and no
significant regressions. This means that Big/Super Pages will only be
used for BOs of at least 512KB.

Signed-off-by: Maíra Canal <mcanal@igalia.com>

Author: mairacanal

drivers/gpu/drm/v3d/v3d_bo.c

@@ -116,7 +116,7 @@ v3d_bo_create_finish(struct drm_gem_object *obj)
 		align = SZ_4K;
 	else if (obj->size >= SZ_1M)
 		align = SZ_1M;
-	else if (obj->size >= SZ_64K)
+	else if (obj->size >= SZ_512K)
 		align = SZ_64K;
 	else
 		align = SZ_4K;
@@ -150,10 +150,14 @@ struct v3d_bo *v3d_bo_create(struct drm_device *dev, struct drm_file *file_priv,
 	struct drm_gem_shmem_object *shmem_obj;
 	struct v3d_dev *v3d = to_v3d_dev(dev);
 	struct v3d_bo *bo;
+	size_t size = PAGE_ALIGN(unaligned_size);
 	int ret;
 
-	shmem_obj = drm_gem_shmem_create_with_mnt(dev, unaligned_size,
-						  v3d->gemfs);
+	if (size >= SZ_512K)
+		shmem_obj = drm_gem_shmem_create_with_mnt(dev, size, v3d->gemfs);
+	else
+		shmem_obj = drm_gem_shmem_create(dev, size);
+
 	if (IS_ERR(shmem_obj))
 		return ERR_CAST(shmem_obj);
 	bo = to_v3d_bo(&shmem_obj->base);