llama: model_loader: add TENSOR_READ_LAZY (#27794)

* llama: model_loader: add TENSOR_GET_ROW_LAZY

* add --tensor-read-lazy

* rename to TENSOR_READ_LAZY

* gen docs

* address comments

common/arg.cpp

@@ -2720,6 +2720,19 @@ common_params_context common_params_parser_init(common_params & params, llama_ex
             else { throw std::invalid_argument("invalid value"); }
         }
     ).set_env("LLAMA_ARG_LOAD_MODE"));
+    add_opt(common_arg(
+        {"--tensor-read-lazy"}, "MODE",
+        "on-demand reading of certain tensors, for example per-layer embeddings (default: auto)\n"
+        "- on: read the rows of such tensors from disk on demand instead of keeping them resident (requires mmap)\n"
+        "- auto: on, but only for tensors larger than 4 GiB\n"
+        "- off: always keep them resident",
+        [](common_params & params, const std::string & value) {
+            /**/ if (value == "on")   { params.tensor_read_lazy = LLAMA_TENSOR_READ_LAZY_ON;   }
+            else if (value == "auto") { params.tensor_read_lazy = LLAMA_TENSOR_READ_LAZY_AUTO; }
+            else if (value == "off")  { params.tensor_read_lazy = LLAMA_TENSOR_READ_LAZY_OFF;  }
+            else { throw std::invalid_argument("invalid value"); }
+        }
+    ).set_env("LLAMA_ARG_TENSOR_READ_LAZY"));
     add_opt(common_arg(
         {"--numa"}, "TYPE",
         "attempt optimizations that help on some NUMA systems\n"

common/common.cpp

@@ -1688,6 +1688,7 @@ struct llama_model_params common_model_params_to_llama(common_params & params) {
     mparams.main_gpu        = params.main_gpu;
     mparams.split_mode      = params.split_mode;
     mparams.load_mode       = params.load_mode;
+    mparams.tensor_read_lazy = params.tensor_read_lazy;
     mparams.tensor_split    = params.tensor_split;
     mparams.check_tensors   = params.check_tensors;
     mparams.use_extra_bufts = !params.no_extra_bufts;

common/common.h

@@ -483,6 +483,8 @@ struct common_params {
     enum llama_split_mode split_mode = LLAMA_SPLIT_MODE_LAYER; // how to split the model across GPUs
     enum llama_load_mode  load_mode  = LLAMA_LOAD_MODE_AUTO; // how to load the model
 
+    enum llama_tensor_read_lazy tensor_read_lazy = LLAMA_TENSOR_READ_LAZY_AUTO; // on-demand reading of tensors marked by the arch
+
     common_cpu_params cpuparams;
     common_cpu_params cpuparams_batch;