Use the same memory for workspace13 and fused_output. (#31531)

Signed-off-by: Andrey Khalyavin <halyavin@yandex-team.ru>

vllm/model_executor/layers/fused_moe/modular_kernel.py

@@ -848,15 +848,17 @@ class FusedMoEModularKernel(torch.nn.Module):
         # We can reuse the memory between cache1 and cache3 because by the
         # time we need cache3, we're done with cache1.
         # Construct the entire output that can then be processed in chunks.
-        # Reuse workspace13 for the output in the non-chunked case as long
-        # as it is large enough. This will not always be the case for standard
+        # Reuse workspace13 for the output in the non-chunked case.
+        # This will not always be the case for standard
         # format experts and with experts that have empty workspaces.
-        if num_chunks == 1 and prod(workspace13_shape) >= prod(fused_out_shape):
-            workspace13, workspace2 = current_workspace_manager().get_simultaneous(
-                (workspace13_shape, workspace_dtype),
+        if num_chunks == 1:
+            max_shape_size = max(prod(workspace13_shape), prod(fused_out_shape))
+            common_workspace, workspace2 = current_workspace_manager().get_simultaneous(
+                ((max_shape_size,), workspace_dtype),
                 (workspace2_shape, workspace_dtype),
             )
-            fused_out = _resize_cache(workspace13, fused_out_shape)
+            workspace13 = _resize_cache(common_workspace, workspace13_shape)
+            fused_out = _resize_cache(common_workspace, fused_out_shape)
         else:
             workspace13, workspace2, fused_out = (
                 current_workspace_manager().get_simultaneous(