[BugFix] Graceful handling of torch symm mem errors. (#27671)

Signed-off-by: ilmarkov <markovilya197@gmail.com>
Co-authored-by: Michael Goin <mgoin64@gmail.com>

vllm/distributed/device_communicators/symm_mem.py

@@ -88,13 +88,21 @@ class SymmMemCommunicator:
             self.max_size = SYMM_MEM_ALL_REDUCE_MAX_SIZES[self.device_capability][
                 self.world_size
             ]
-
+        try:
             self.buffer = torch_symm_mem.empty(
                 self.max_size // self.dtype.itemsize,
                 device=self.device,
                 dtype=self.dtype,
             )
             handle = torch_symm_mem.rendezvous(self.buffer, self.group.group_name)
+        except RuntimeError as e:
+            logger.warning_once(
+                "SymmMemCommunicator: symmetric memory initialization failed: %s "
+                "Communicator is not available. To suppress this warning set "
+                "VLLM_ALLREDUCE_USE_SYMM_MEM=0",
+                str(e),
+            )
+            return
         if handle.multicast_ptr == 0:
             logger.warning(
                 "SymmMemCommunicator: symmetric memory "

vllm/envs.py

@@ -201,7 +201,7 @@ if TYPE_CHECKING:
     VLLM_USE_FLASHINFER_MOE_MXFP4_BF16: bool = False
     VLLM_ROCM_FP8_MFMA_PAGE_ATTN: bool = False
     VLLM_USE_FLASHINFER_MOE_MXFP4_MXFP8_CUTLASS: bool = False
-    VLLM_ALLREDUCE_USE_SYMM_MEM: bool = False
+    VLLM_ALLREDUCE_USE_SYMM_MEM: bool = True
     VLLM_TUNED_CONFIG_FOLDER: str | None = None
     VLLM_GPT_OSS_SYSTEM_TOOL_MCP_LABELS: set[str] = set()
     VLLM_GPT_OSS_HARMONY_SYSTEM_INSTRUCTIONS: bool = False
@@ -1389,7 +1389,7 @@ environment_variables: dict[str, Callable[[], Any]] = {
     ),
     # Whether to use pytorch symmetric memory for allreduce
     "VLLM_ALLREDUCE_USE_SYMM_MEM": lambda: bool(
-        int(os.getenv("VLLM_ALLREDUCE_USE_SYMM_MEM", "0"))
+        int(os.getenv("VLLM_ALLREDUCE_USE_SYMM_MEM", "1"))
     ),
     # Allows vllm to find tuned config under customized folder
     "VLLM_TUNED_CONFIG_FOLDER": lambda: os.getenv("VLLM_TUNED_CONFIG_FOLDER", None),