drm/amdgpu: restructure amdgpu_vram_mgr_new

Merge the two loops, loosen the restriction for big allocations.
This reduces the CPU overhead in the good case, but increases
it a bit under memory pressure.
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-and-Tested-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c

@@ -358,13 +358,13 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
 			       const struct ttm_place *place,
 			       struct ttm_resource *mem)
 {
+	unsigned long lpfn, num_nodes, pages_per_node, pages_left, pages;
 	struct amdgpu_vram_mgr *mgr = to_vram_mgr(man);
 	struct amdgpu_device *adev = to_amdgpu_device(mgr);
+	uint64_t vis_usage = 0, mem_bytes, max_bytes;
 	struct drm_mm *mm = &mgr->mm;
-	struct drm_mm_node *nodes;
 	enum drm_mm_insert_mode mode;
-	unsigned long lpfn, num_nodes, pages_per_node, pages_left;
-	uint64_t vis_usage = 0, mem_bytes, max_bytes;
+	struct drm_mm_node *nodes;
 	unsigned i;
 	int r;
 
@@ -391,9 +391,10 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
 		pages_per_node = HPAGE_PMD_NR;
 #else
 		/* default to 2MB */
-		pages_per_node = (2UL << (20UL - PAGE_SHIFT));
+		pages_per_node = 2UL << (20UL - PAGE_SHIFT);
 #endif
-		pages_per_node = max((uint32_t)pages_per_node, mem->page_alignment);
+		pages_per_node = max_t(uint32_t, pages_per_node,
+				       mem->page_alignment);
 		num_nodes = DIV_ROUND_UP(mem->num_pages, pages_per_node);
 	}
 
@@ -411,42 +412,37 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
 	mem->start = 0;
 	pages_left = mem->num_pages;
 
-	spin_lock(&mgr->lock);
-	for (i = 0; pages_left >= pages_per_node; ++i) {
-		unsigned long pages = rounddown_pow_of_two(pages_left);
-
-		/* Limit maximum size to 2GB due to SG table limitations */
-		pages = min(pages, (2UL << (30 - PAGE_SHIFT)));
+	/* Limit maximum size to 2GB due to SG table limitations */
+	pages = min(pages_left, 2UL << (30 - PAGE_SHIFT));
 
-		r = drm_mm_insert_node_in_range(mm, &nodes[i], pages,
-						pages_per_node, 0,
-						place->fpfn, lpfn,
-						mode);
-		if (unlikely(r))
-			break;
-
-		vis_usage += amdgpu_vram_mgr_vis_size(adev, &nodes[i]);
-		amdgpu_vram_mgr_virt_start(mem, &nodes[i]);
-		pages_left -= pages;
-	}
-
-	for (; pages_left; ++i) {
-		unsigned long pages = min(pages_left, pages_per_node);
+	i = 0;
+	spin_lock(&mgr->lock);
+	while (pages_left) {
 		uint32_t alignment = mem->page_alignment;
 
-		if (pages == pages_per_node)
+		if (pages >= pages_per_node)
 			alignment = pages_per_node;
 
-		r = drm_mm_insert_node_in_range(mm, &nodes[i],
-						pages, alignment, 0,
-						place->fpfn, lpfn,
-						mode);
-		if (unlikely(r))
+		r = drm_mm_insert_node_in_range(mm, &nodes[i], pages, alignment,
+						0, place->fpfn, lpfn, mode);
+		if (unlikely(r)) {
+			if (pages > pages_per_node) {
+				if (is_power_of_2(pages))
+					pages = pages / 2;
+				else
+					pages = rounddown_pow_of_two(pages);
+				continue;
+			}
 			goto error;
+		}
 
 		vis_usage += amdgpu_vram_mgr_vis_size(adev, &nodes[i]);
 		amdgpu_vram_mgr_virt_start(mem, &nodes[i]);
 		pages_left -= pages;
+		++i;
+
+		if (pages > pages_left)
+			pages = pages_left;
 	}
 	spin_unlock(&mgr->lock);