ggml : use CL_DEVICE_GLOBAL_MEM_SIZE as memory estimate for OpenCL --fit (ggml-org#22688)

* ggml : report estimated OpenCL memory for --fit

Signed-off-by: Florian Reinle <f.reinle@otec.de>

* ggml : estimated OpenCL memory backend integrated

Signed-off-by: Florian Reinle <f.reinle@otec.de>

---------

Signed-off-by: Florian Reinle <f.reinle@otec.de>

Author: fl0rianr

ggml/src/ggml-opencl/ggml-opencl.cpp

@@ -389,6 +389,7 @@ struct ggml_backend_opencl_context {
     ADRENO_GPU_GEN adreno_gen;
 
     cl_int alignment;
+    size_t global_mem_size;
     size_t max_alloc_size;
     size_t max_workgroup_size;
     bool fp16_support;
@@ -3386,6 +3387,9 @@ static ggml_backend_opencl_context * ggml_cl2_init(ggml_backend_dev_t dev) {
     backend_ctx->alignment = base_align_in_bits / 8u;
     GGML_LOG_INFO("ggml_opencl: mem base addr align: %u\n", backend_ctx->alignment);
 
+    clGetDeviceInfo(device, CL_DEVICE_GLOBAL_MEM_SIZE, sizeof(size_t), &backend_ctx->global_mem_size, NULL);
+    GGML_LOG_INFO("ggml_opencl: global mem size: %zu MB\n", backend_ctx->global_mem_size/1024/1024);
+
     clGetDeviceInfo(device, CL_DEVICE_MAX_MEM_ALLOC_SIZE, sizeof(size_t), &backend_ctx->max_alloc_size, NULL);
     GGML_LOG_INFO("ggml_opencl: max mem alloc size: %zu MB\n", backend_ctx->max_alloc_size/1024/1024);
 
@@ -6356,11 +6360,16 @@ static const char * ggml_backend_opencl_device_get_description(ggml_backend_dev_
 }
 
 static void ggml_backend_opencl_device_get_memory(ggml_backend_dev_t dev, size_t * free, size_t * total) {
-    // no memory to report
-    *free  = 0;
-    *total = 0;
+    ggml_backend_opencl_device_context * dev_ctx = (ggml_backend_opencl_device_context *) dev->context;
+    ggml_backend_opencl_context * backend_ctx = (ggml_backend_opencl_context *) dev_ctx->backend_ctx;
 
-    GGML_UNUSED(dev);
+    static const size_t opencl_extra_margin = 1024ull*1024ull*1024ull;
+
+    // OpenCL does not provide reliable currently-free device memory.
+    // Use total/global memory as a best-effort upper bound.
+    // Improved safety: Reduce by a 1GiB extra margin for common --fit
+    *total = backend_ctx->global_mem_size;
+    *free  = *total > opencl_extra_margin ? *total - opencl_extra_margin : 0;
 }
 
 static enum ggml_backend_dev_type ggml_backend_opencl_device_get_type(ggml_backend_dev_t dev) {