Re: [PATCH v2] drm/amdkfd: check system memory when set apu_prefer_gtt

[Mario Limonciello]

On 3/19/2026 2:32 AM, Yifan Zhang wrote:
Current apu_prefer_gtt setting only check gtt_size, which could be set
by user to a larger than system memory value (via ttm modules parameter
pages_limit). E.g. carveout vram 32GB, gtt_size 50GB (via ttm modules
parameter pages_limit), system memory 31GB. In that case, apu_prefer_gtt
will be set incorrectly. Take system memory into account when set
apu_prefer_gtt.


Wouldn't it be cleaner to do this in TTM?  IE test that a bad option was 
set by user pages_limit value and then show something like:

if (user > possible) {
    pr_warn("Requested invalid %d pages, limiting to %d pages", user, 
possible);
    user = possible;
}

Then we can always trust what we get from TTM.

Signed-off-by: Yifan Zhang <yifan1.zh...@amd.com>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c       | 2 --
  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h       | 4 ++--
  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 6 ++++--
  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c          | 7 ++++++-
  4 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c
index 3bfd79c89df3..a6ee9d9bfafb 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c
@@ -170,8 +170,6 @@ void amdgpu_amdkfd_device_init(struct amdgpu_device *adev)
        int i;
        int last_valid_bit;
  
-	amdgpu_amdkfd_gpuvm_init_mem_limits();
-
        if (adev->kfd.dev) {
                struct kgd2kfd_shared_resources gpu_resources = {
                        .compute_vmid_bitmap =
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
index cdbab7f8cee8..13cada7da4a9 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
@@ -369,7 +369,7 @@ u64 amdgpu_amdkfd_xcp_memory_size(struct amdgpu_device 
*adev, int xcp_id);
  
  
  #if IS_ENABLED(CONFIG_HSA_AMD)
-void amdgpu_amdkfd_gpuvm_init_mem_limits(void);
+uint64_t amdgpu_amdkfd_gpuvm_init_mem_limits(void);
  void amdgpu_amdkfd_gpuvm_destroy_cb(struct amdgpu_device *adev,
                                struct amdgpu_vm *vm);
  
@@ -382,7 +382,7 @@ void amdgpu_amdkfd_release_notify(struct amdgpu_bo *bo);
  void amdgpu_amdkfd_reserve_system_mem(uint64_t size);
  #else
  static inline
-void amdgpu_amdkfd_gpuvm_init_mem_limits(void)
+uint64_t amdgpu_amdkfd_gpuvm_init_mem_limits(void)
  {
  }
  
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index 8a869fe41acd..4fba7d2f34a9 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -109,13 +109,13 @@ static bool reuse_dmamap(struct amdgpu_device *adev, 
struct amdgpu_device *bo_ad
   *  System (TTM + userptr) memory - 15/16th System RAM
   *  TTM memory - 3/8th System RAM
   */
-void amdgpu_amdkfd_gpuvm_init_mem_limits(void)
+uint64_t amdgpu_amdkfd_gpuvm_init_mem_limits(void)
  {
        struct sysinfo si;
        uint64_t mem;
  
  	if (kfd_mem_limit.max_system_mem_limit)
-               return;
+               return kfd_mem_limit.max_system_mem_limit;
  
  	si_meminfo(&si);
        mem = si.totalram - si.totalhigh;
@@ -132,6 +132,8 @@ void amdgpu_amdkfd_gpuvm_init_mem_limits(void)
        pr_debug("Kernel memory limit %lluM, TTM limit %lluM\n",
                (kfd_mem_limit.max_system_mem_limit >> 20),
                (kfd_mem_limit.max_ttm_mem_limit >> 20));
+
+       return kfd_mem_limit.max_system_mem_limit;
  }
  
  void amdgpu_amdkfd_reserve_system_mem(uint64_t size)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 714fd8d12ca5..df98ece071e1 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -2071,6 +2071,7 @@ static void amdgpu_ttm_buffer_entity_fini(struct 
amdgpu_gtt_mgr *mgr,
  int amdgpu_ttm_init(struct amdgpu_device *adev)
  {
        uint64_t gtt_size;
+       uint64_t max_system_mem_limit;
        int r;
  
  	dma_set_max_seg_size(adev->dev, UINT_MAX);
@@ -2210,8 +2211,12 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
        dev_info(adev->dev, " %uM of GTT memory ready.\n",
                 (unsigned int)(gtt_size / (1024 * 1024)));
  
+
+       max_system_mem_limit = amdgpu_amdkfd_gpuvm_init_mem_limits();
+
        if (adev->flags & AMD_IS_APU) {
-               if (adev->gmc.real_vram_size < gtt_size)
+               if (adev->gmc.real_vram_size < gtt_size &&
+                       adev->gmc.real_vram_size < max_system_mem_limit)
                        adev->apu_prefer_gtt = true;
        }