[https://nvbugs/5412562][feat] Allocate MoE workspace only when necessary (release/1.0 retargeted) (#6955)

Signed-off-by: Yilin Fan <[email protected]>

Author: nv-yilinf

cpp/tensorrt_llm/thop/moeOp.cpp

@@ -308,8 +308,8 @@ class FusedMoeRunner : public torch::CustomClassHolder
         std::vector<int64_t> output_shape = {num_rows, hidden_size};
         auto output = torch::empty(output_shape, input.options().dtype(mOutputDtype));
 
-        WorkspaceInfo workspace_info = getWorkspaceInfo(num_rows, hidden_size, inter_size, num_experts_total,
-            static_cast<int>(experts_per_token), activation_type, parallelism_config, min_latency_mode);
+        WorkspaceInfo const& workspace_info = getWorkspaceInfo(num_rows, hidden_size, inter_size, num_experts_total,
+            static_cast<int>(experts_per_token), activation_type, parallelism_config, min_latency_mode, stream);
 
         auto const quant_params = getQuantParams(num_experts_on_rank, hidden_size, inter_size, quant_scales);
         kernels::MoeMinLatencyParams min_latency_params{};
@@ -439,8 +439,8 @@ class FusedMoeRunner : public torch::CustomClassHolder
         min_latency_params.experts_to_token_score = static_cast<float*>(experts_to_token_score.data_ptr());
         min_latency_params.active_expert_global_ids = static_cast<int*>(active_expert_global_ids.data_ptr());
 
-        WorkspaceInfo workspace_info = getWorkspaceInfo(num_rows, hidden_size, inter_size, num_experts_total,
-            static_cast<int>(experts_per_token), activation_type, parallelism_config, min_latency_mode);
+        WorkspaceInfo const& workspace_info = getWorkspaceInfo(num_rows, hidden_size, inter_size, num_experts_total,
+            static_cast<int>(experts_per_token), activation_type, parallelism_config, min_latency_mode, stream);
 
         auto const quant_params = getQuantParams(num_experts_on_rank, hidden_size, inter_size, quant_scales);
 
@@ -577,6 +577,7 @@ class FusedMoeRunner : public torch::CustomClassHolder
     // e.g. 16 nvfp4 elements are packed into a single int64 element
     int64_t mInnerDimMultiplier;
     char* mProfileWorkspace = nullptr;
+    WorkspaceInfo workspace_info;
 
     bool mUseDeepSeekFP8BlockScaling = false;
     bool mUseW4A8GroupScaling = false;
@@ -622,9 +623,9 @@ class FusedMoeRunner : public torch::CustomClassHolder
         mKernelRunner->setTactic(best_gemm1_profile, best_gemm2_profile);
     }
 
-    WorkspaceInfo getWorkspaceInfo(int64_t const num_rows, int64_t const hidden_size, int64_t const inter_size,
+    WorkspaceInfo const& getWorkspaceInfo(int64_t const num_rows, int64_t const hidden_size, int64_t const inter_size,
         int num_experts, int experts_per_token, ActivationType activation_type,
-        kernels::MOEParallelismConfig const& parallelismConfig, bool min_latency_mode)
+        kernels::MOEParallelismConfig const& parallelismConfig, bool min_latency_mode, cudaStream_t stream)
     {
         size_t moe_workspace_size = mKernelRunner->getWorkspaceSize(num_rows, hidden_size, inter_size, num_experts,
             experts_per_token, activation_type, parallelismConfig, /* use_lora */ false, mUseDeepSeekFP8BlockScaling,
@@ -633,15 +634,29 @@ class FusedMoeRunner : public torch::CustomClassHolder
 
         std::vector<size_t> workspaces{moe_workspace_size, src_to_dest_map_size};
 
-        size_t total_workspace_size = common::calculateTotalWorkspaceSize(workspaces.data(), workspaces.size());
+        int64_t const total_workspace_size = common::calculateTotalWorkspaceSize(workspaces.data(), workspaces.size());
 
-        WorkspaceInfo info{};
-        info.workspace = torch::empty({static_cast<long>(total_workspace_size)},
-            torch::dtype(torch::kInt8).device(torch::kCUDA).requires_grad(false));
-        info.src_to_dest_map
-            = common::nextWorkspacePtr(static_cast<int8_t*>(info.workspace.data_ptr()), moe_workspace_size);
+        bool is_capturing = tensorrt_llm::common::isCapturing(stream);
+        // Always allocate workspace when capturing cuda graph to avoid illegal memory access during replay
+        if (is_capturing || workspace_info.workspace.numel() < total_workspace_size)
+        {
+            if (is_capturing)
+            {
+                TLLM_LOG_DEBUG(
+                    "Allocating MoE workspace with %ld bytes size during cuda graph capture", total_workspace_size);
+            }
+            else
+            {
+                TLLM_LOG_DEBUG("MoE workspace size is not enough, increase the size from %ld bytes to %ld bytes",
+                    workspace_info.workspace.numel(), total_workspace_size);
+            }
+            workspace_info.workspace = torch::empty({static_cast<long>(total_workspace_size)},
+                torch::dtype(torch::kInt8).device(torch::kCUDA).requires_grad(false));
+        }
+        workspace_info.src_to_dest_map
+            = common::nextWorkspacePtr(static_cast<int8_t*>(workspace_info.workspace.data_ptr()), moe_workspace_size);
 
-        return info;
+        return workspace_info;
     }
 
     kernels::QuantParams getQuantParams(int64_t const num_experts_on_rank, int64_t const hidden_size,