drm/amdgpu: Adjust the VM size based on system memory size v2

Set the VM size based on system memory size between the ASIC-specific
limits given by min_vm_size and max_bits. GFXv9 GPUs will keep their
default VM size of 256TB (48 bit). Only older GPUs will adjust VM size
depending on system memory size.

This makes more VM space available for ROCm applications on GFXv8 GPUs
that want to map all available VRAM and system memory in their SVM
address space.

v2:
* Clarify comment
* Round up memory size before >> 30
* Round up automatic vm_size to power of two
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Junwei Zhang <Jerry.Zhang@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2504,28 +2504,52 @@ static uint32_t amdgpu_vm_get_block_size(uint64_t vm_size)
  * amdgpu_vm_adjust_size - adjust vm size, block size and fragment size
  *
  * @adev: amdgpu_device pointer
- * @vm_size: the default vm size if it's set auto
+ * @min_vm_size: the minimum vm size in GB if it's set auto
  * @fragment_size_default: Default PTE fragment size
  * @max_level: max VMPT level
  * @max_bits: max address space size in bits
  *
  */
-void amdgpu_vm_adjust_size(struct amdgpu_device *adev, uint32_t vm_size,
+void amdgpu_vm_adjust_size(struct amdgpu_device *adev, uint32_t min_vm_size,
 			   uint32_t fragment_size_default, unsigned max_level,
 			   unsigned max_bits)
 {
+	unsigned int max_size = 1 << (max_bits - 30);
+	unsigned int vm_size;
 	uint64_t tmp;
 
 	/* adjust vm size first */
 	if (amdgpu_vm_size != -1) {
-		unsigned max_size = 1 << (max_bits - 30);
-
 		vm_size = amdgpu_vm_size;
 		if (vm_size > max_size) {
 			dev_warn(adev->dev, "VM size (%d) too large, max is %u GB\n",
 				 amdgpu_vm_size, max_size);
 			vm_size = max_size;
 		}
+	} else {
+		struct sysinfo si;
+		unsigned int phys_ram_gb;
+
+		/* Optimal VM size depends on the amount of physical
+		 * RAM available. Underlying requirements and
+		 * assumptions:
+		 *
+		 *  - Need to map system memory and VRAM from all GPUs
+		 *     - VRAM from other GPUs not known here
+		 *     - Assume VRAM <= system memory
+		 *  - On GFX8 and older, VM space can be segmented for
+		 *    different MTYPEs
+		 *  - Need to allow room for fragmentation, guard pages etc.
+		 *
+		 * This adds up to a rough guess of system memory x3.
+		 * Round up to power of two to maximize the available
+		 * VM size with the given page table size.
+		 */
+		si_meminfo(&si);
+		phys_ram_gb = ((uint64_t)si.totalram * si.mem_unit +
+			       (1 << 30) - 1) >> 30;
+		vm_size = roundup_pow_of_two(
+			min(max(phys_ram_gb * 3, min_vm_size), max_size));
 	}
 
 	adev->vm_manager.max_pfn = (uint64_t)vm_size << 18;

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h

@@ -351,7 +351,7 @@ struct amdgpu_bo_va_mapping *amdgpu_vm_bo_lookup_mapping(struct amdgpu_vm *vm,
 void amdgpu_vm_bo_trace_cs(struct amdgpu_vm *vm, struct ww_acquire_ctx *ticket);
 void amdgpu_vm_bo_rmv(struct amdgpu_device *adev,
 		      struct amdgpu_bo_va *bo_va);
-void amdgpu_vm_adjust_size(struct amdgpu_device *adev, uint32_t vm_size,
+void amdgpu_vm_adjust_size(struct amdgpu_device *adev, uint32_t min_vm_size,
 			   uint32_t fragment_size_default, unsigned max_level,
 			   unsigned max_bits);
 int amdgpu_vm_ioctl(struct drm_device *dev, void *data, struct drm_file *filp);