[C++] Invoke storage allocation for CUDA Graph explicitly (#3042)

This PR adds a function that invokes the storage allocation function
generated by CUDA Graph rewrite. With this function, we now manually
trigger the storage allocation at initialization time.

The reason we need this is because that the storage allocation may
contain CUDA IPC memory alloc that has to run through a Disco session.
So when a function that needs CUDA graph storage allocation runs first
outside a Disco session, there might be error caused if we did not
initialize the allocation in advance.

Author: MasterJH5574

cpp/serve/function_table.cc

@@ -152,6 +152,10 @@ void FunctionTable::Init(String reload_lib_path, Device device, picojson::object
   }
   ICHECK_EQ(this->model_metadata_.tensor_parallel_shards, num_shards);
   ICHECK_EQ(this->model_metadata_.pipeline_parallel_stages, num_stages);
+  // Invoke the CUDA graph allocation init function if it is defined.
+  if (cuda_graph_alloc_init_func_.defined()) {
+    this->cuda_graph_alloc_init_func_();
+  }
 }
 
 ObjectRef FunctionTable::LoadParams(const std::string& model_path, Device device) {
@@ -231,6 +235,7 @@ void FunctionTable::_InitFunctions() {
   this->apply_penalty_func_ = mod->GetFunction("apply_penalty_inplace", true);
   this->apply_bitmask_func_ = mod->GetFunction("apply_bitmask_inplace", true);
   this->alloc_embedding_tensor_func_ = mod_get_func("alloc_embedding_tensor");
+  this->cuda_graph_alloc_init_func_ = mod_get_func("cuda_graph_alloc_init");
   this->create_kv_cache_func_ = mod_get_func("create_flashinfer_paged_kv_cache");
   if (this->model_metadata_.sliding_window_size != -1 || !this->create_kv_cache_func_.defined()) {
     PackedFunc f_create_rnn_state = mod_get_func("create_rnn_state");

cpp/serve/function_table.h

@@ -99,6 +99,7 @@ struct FunctionTable {
   PackedFunc apply_penalty_func_;
   PackedFunc apply_bitmask_func_;
   PackedFunc alloc_embedding_tensor_func_;
+  PackedFunc cuda_graph_alloc_init_func_;
   PackedFunc create_kv_cache_func_;
   PackedFunc reset_kv_cache_func_;
   bool support_backtracking_kv_;

python/mlc_llm/compiler_pass/attach_cuda_graph_alloc_init_func.py

@@ -0,0 +1,33 @@
+"""The pass that attaches an empty function for initialization."""
+
+import tvm
+from tvm import IRModule, relax
+
+
+@tvm.transform.module_pass(opt_level=0, name="AttachCUDAGraphAllocInitFunc")
+class AttachCUDAGraphAllocInitFunc:  # pylint: disable=too-few-public-methods
+    """Attach an empty function for initialization."""
+
+    def __init__(self):
+        pass
+
+    def transform_module(self, mod: IRModule, _ctx: tvm.transform.PassContext) -> IRModule:
+        """Entrypoint"""
+        bb = relax.BlockBuilder(mod)
+        alloc_func_gv = None
+        for gv, _ in mod.functions_items():
+            if gv.name_hint.startswith("cuda_graph_alloc"):
+                assert alloc_func_gv is None
+                alloc_func_gv = gv
+        if alloc_func_gv is None:
+            return mod
+
+        with bb.function("cuda_graph_alloc_init", []):
+            bb.emit_func_output(
+                relax.op.call_builtin_with_ctx(
+                    "vm.builtin.cuda_graph.get_cached_alloc",
+                    args=[alloc_func_gv, relax.PrimValue(0)],
+                    sinfo_args=relax.ObjectStructInfo(),
+                )
+            )
+        return bb.finalize()

python/mlc_llm/compiler_pass/pipeline.py

@@ -12,6 +12,7 @@
 from mlc_llm.interface.compiler_flags import IPCAllReduceStrategyType
 from mlc_llm.support import logging
 
+from .attach_cuda_graph_alloc_init_func import AttachCUDAGraphAllocInitFunc
 from .attach_embedding_allocator import AttachAllocEmbeddingTensorFunc
 from .attach_logit_processor import AttachLogitProcessFunc
 from .attach_sampler import AttachGPUSamplingFunc
@@ -159,7 +160,6 @@ def _pipeline(mod: tvm.ir.IRModule, _ctx: tvm.transform.PassContext) -> tvm.ir.I
                 ),
                 ScatterTupleGetItem(),
                 PipelineParallelRewrite(),
-                _DebugDump("after-pipeline-rewrite.py", debug_dump, show_meta=False),
                 tvm.relax.transform.RewriteDataflowReshape(),
                 tvm.relax.transform.ToNonDataflow(),
                 tvm.relax.transform.RemovePurityChecking(),
@@ -172,6 +172,7 @@ def _pipeline(mod: tvm.ir.IRModule, _ctx: tvm.transform.PassContext) -> tvm.ir.I
                 tvm.relax.transform.StaticPlanBlockMemory(),
                 AttachMetadataWithMemoryUsage(metadata),
                 tvm.relax.transform.RewriteCUDAGraph(),
+                AttachCUDAGraphAllocInitFunc(),
                 tvm.relax.transform.LowerGPUIPCAllocStorage(),
                 tvm.relax.transform.LowerAllocTensor(),
                 tvm.relax.transform.KillAfterLastUse(),