[Bug] Fix Trtllm Fp8 MoE Weight Shuffle Memory Fragamentation (#39054)

Signed-off-by: wzhao18 <wzhao18.sz@gmail.com>

vllm/model_executor/layers/quantization/utils/flashinfer_utils.py

@@ -322,20 +322,23 @@ def _shuffle_deepseek_fp8_moe_weights(
     block_k = 128
     num_experts = w13.shape[0]
 
-    w13_shuffled: list[torch.Tensor] = []
-    w2_shuffled: list[torch.Tensor] = []
+    M13, K13 = w13.shape[1], w13.shape[2]
+    M2, K2 = w2.shape[1], w2.shape[2]
+    w13_out = torch.empty(
+        num_experts, K13 // block_k, M13, block_k, dtype=torch.uint8, device=w13.device
+    )
+    w2_out = torch.empty(
+        num_experts, K2 // block_k, M2, block_k, dtype=torch.uint8, device=w2.device
+    )
+
     for i in range(num_experts):
         t13 = shuffle_matrix_a(w13[i].view(torch.uint8), epilogue_tile_m)
-        t13 = convert_to_block_layout(t13, block_k)
-        w13_shuffled.append(t13)
+        w13_out[i] = convert_to_block_layout(t13, block_k)
 
         t2 = shuffle_matrix_a(w2[i].view(torch.uint8), epilogue_tile_m)
-        t2 = convert_to_block_layout(t2, block_k)
-        w2_shuffled.append(t2)
+        w2_out[i] = convert_to_block_layout(t2, block_k)
 
-    w13_out = torch.stack(w13_shuffled).view(torch.float8_e4m3fn)
-    w2_out = torch.stack(w2_shuffled).view(torch.float8_e4m3fn)
-    return w13_out, w2_out
+    return w13_out.view(torch.float8_e4m3fn), w2_out.view(torch.float8_e4m3fn)
 
 
 def _shuffle_mxfp8_moe_weights(