sycl : support limit max alloc memory within 2GB for host-pinned memory (#27559)

docs/backend/SYCL.md

@@ -795,7 +795,8 @@ User can use the device management in [docs/multi-gpu.md](https://github.com/ggm
 | GGML_SYCL_ENABLE_FLASH_ATTN | 1 (default) or 0| Enable Flash-Attention. It can reduce memory usage. The performance impact depends on the LLM.|
 | GGML_SYCL_ENABLE_OPT | 0 or 1 (default)| Enable optimize features for Intel GPUs. (Recommended to 0 for Intel devices older than Gen 10) |
 | GGML_SYCL_ENABLE_GRAPH | 0 (default) or 1 | Enable running computations through SYCL Graphs feature. Disabled by default because SYCL Graph is still on development, no better performance. |
-| GGML_SYCL_ENABLE_HOST_PINNED_MEM | 0 or 1 (default) | Enable host pinned memory to speed up copy data from host to device. When disable it, host memory will common malloc() on CPU.|
+| GGML_SYCL_ENABLE_HOST_PINNED_MEM | 0 or 1 (default) | Enable host pinned memory to speed up copy data from host to device. When disable it, host memory will common malloc() on CPU. Disable it when use `--load-model mlock`.|
+| GGML_SYCL_HOST_PINNED_MEM_2G | 0 (default) or 1 | Limit the max memory allocation to be no more than 2GB when enable host pinned memory. USM allocations above 2 GiB take the relaxed/large-allocation path, which serializes H2D copies with compute and prevents copy/compute overlap. It will impact the startup time. Need more test. Depend on `GGML_SYCL_ENABLE_HOST_PINNED_MEM=1`.|
 | GGML_SYCL_GET_MEM_API | 0 (default) or 1  | Set to get memory info (free, total) by Level Zero or SYCL API:<br>0 - Level Zero API: support more GPUs, only run on Level Zero running time. When there is an error, fallback to call SYCL API. Depend on GGML_SYCL_SUPPORT_LEVEL_ZERO_API.<br>1 - SYCL API: legacy, support more running time, it can't get the free size of some GPUs (like Arc770). In such case, return total size for free size.|
 | GGML_SYCL_USE_LEVEL_ZERO_API | 1 (default) or 0 | Use Level Zero API for device memory allocation instead of SYCL. Reduces system RAM usage on Intel dGPUs by avoiding DMA-buf/TTM host memory staging. Requires GGML_SYCL_SUPPORT_LEVEL_ZERO_API=ON at build time. SYCL backend always runs on Level Zero running time even if it's set as OFF (The SYCL api will be usage for memory allocation).|
 | GGML_SYCL_ENABLE_DNN | 0 or 1 (default)| Enable running computations through oneDNN and always use oneMKL. |

ggml/src/ggml-sycl/ggml-sycl.cpp

@@ -107,6 +107,7 @@ int g_ggml_sycl_enable_flash_attention = 1;
 int g_ggml_sycl_dev2dev_memcpy = DEV2DEV_MEMCPY_SYCL;
 int g_ggml_sycl_usm_system = 0;
 int g_ggml_sycl_enable_host_pinned_mem = 1;
+int g_ggml_sycl_host_pinned_mem_2g = 0;
 int g_ggml_sycl_get_mem_api = MEMORY_API_TYPE_LEVEL_ZERO;
 
 
@@ -355,6 +356,8 @@ static void ggml_check_sycl() try {
         g_ggml_sycl_enable_host_pinned_mem =
             ggml_sycl_get_env("GGML_SYCL_ENABLE_HOST_PINNED_MEM", 1);
 
+        g_ggml_sycl_host_pinned_mem_2g =
+            ggml_sycl_get_env("GGML_SYCL_HOST_PINNED_MEM_2G", 0) & g_ggml_sycl_enable_host_pinned_mem;
 
         GGML_SYCL_DEBUG("[SYCL] call ggml_check_sycl\n");
 
@@ -457,6 +460,7 @@ static void ggml_check_sycl() try {
 
         GGML_LOG_INFO("  GGML_SYCL_USM_SYSTEM: %d\n", g_ggml_sycl_usm_system);
         GGML_LOG_INFO("  GGML_SYCL_ENABLE_HOST_PINNED_MEM: %d\n", g_ggml_sycl_enable_host_pinned_mem);
+        GGML_LOG_INFO("  GGML_SYCL_HOST_PINNED_MEM_2G: %d\n", g_ggml_sycl_host_pinned_mem_2g);
 
 /* NOT REMOVE, keep it for next optimize for XMX.
 #if defined(SYCL_USE_XMX)
@@ -977,8 +981,12 @@ static size_t ggml_backend_sycl_buffer_type_get_alignment(ggml_backend_buffer_ty
 }
 
 static size_t ggml_backend_sycl_buffer_type_get_max_size(ggml_backend_buffer_type_t buft) {
-    return dpct::get_current_device().get_max_mem_alloc_size();
-
+    size_t max_alloc_size = dpct::get_current_device().get_max_mem_alloc_size();
+    if (g_ggml_sycl_host_pinned_mem_2g) {
+        return std::min(max_alloc_size, (size_t) 2LL*1024*1024*1024);
+    } else {
+        return max_alloc_size;
+    }
     GGML_UNUSED(buft);
 }
 
@@ -1551,7 +1559,12 @@ static size_t ggml_backend_sycl_host_buffer_type_get_max_size(ggml_backend_buffe
 
     if (g_ggml_sycl_enable_host_pinned_mem) {
         ggml_backend_sycl_device_context * dev_ctx = (ggml_backend_sycl_device_context *) buft->device->context;
-        return dpct::dev_mgr::instance().get_device(dev_ctx->device).get_max_mem_alloc_size();
+        size_t max_alloc_size = dpct::dev_mgr::instance().get_device(dev_ctx->device).get_max_mem_alloc_size();
+        if (g_ggml_sycl_host_pinned_mem_2g) {
+            return std::min(max_alloc_size, (size_t) 2LL*1024*1024*1024);
+        } else {
+            return max_alloc_size;
+        }
     } else {
         return SIZE_MAX;
     }