llama : quantize up to 31% faster on Linux and Windows with mmap (#3206)

* llama : enable mmap in quantize on Linux -> 31% faster

* also enable mmap on Windows

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

llama.cpp

@@ -6027,7 +6027,18 @@ static void llama_model_quantize_internal(const std::string & fname_inp, const s
         nthread = std::thread::hardware_concurrency();
     }
 
-    llama_model_loader ml(fname_inp, /*use_mmap*/ false);
+    // mmap consistently increases speed Linux, and also increases speed on Windows with
+    // hot cache. It may cause a slowdown on macOS, possibly related to free memory.
+#if defined(__linux__) || defined(_WIN32)
+    constexpr bool use_mmap = true;
+#else
+    constexpr bool use_mmap = false;
+#endif
+
+    llama_model_loader ml(fname_inp, use_mmap);
+    if (ml.use_mmap) {
+        ml.mapping.reset(new llama_mmap(&ml.file, /* prefetch */ 0, ggml_is_numa()));
+    }
 
     llama_model model;
     llm_load_arch(ml, model);
@@ -6105,10 +6116,12 @@ static void llama_model_quantize_internal(const std::string & fname_inp, const s
 
         const std::string name = ggml_get_name(tensor);
 
-        if (read_data.size() < ggml_nbytes(tensor)) {
-            read_data.resize(ggml_nbytes(tensor));
+        if (!ml.use_mmap) {
+            if (read_data.size() < ggml_nbytes(tensor)) {
+                read_data.resize(ggml_nbytes(tensor));
+            }
+            tensor->data = read_data.data();
         }
-        tensor->data = read_data.data();
         ml.load_data_for(tensor);
 
         LLAMA_LOG_INFO("[%4d/%4d] %36s - [%s], type = %6s, ",