fix: skip cuda graphs that will oom and improve free memory logging

server/text_generation_server/models/flash_causal_lm.py

@@ -1231,6 +1231,13 @@ class FlashCausalLM(Model):
         torch.cuda.synchronize()
 
     def warmup(self, batch: FlashCausalLMBatch):
+        inital_free_memory = get_free_memory(self.device, MEMORY_FRACTION)
+
+        log_master(
+            logger.info,
+            f"Free memory before the warmup: {inital_free_memory/1024/1024:.2f} MB",
+        )
+
         # The warmup batch is the biggest batch we could ever receive
         empty_cache()
 
@@ -1284,6 +1291,15 @@ class FlashCausalLM(Model):
             self.device,
         )
 
+        # cuda graphs must fit within the new memory limit. In order to avoid an OOM, we
+        # need to exit early if there is not enough memory to fit a particular cuda graph
+        free_memory_post_alloc = get_free_memory(self.device, MEMORY_FRACTION)
+
+        log_master(
+            logger.info,
+            f"Free memory after allocating the cache: {free_memory_post_alloc/1024/1024:.2f} MB",
+        )
+
         if SYSTEM == "rocm":
             if (
                 os.environ.get("PYTORCH_TUNABLEOP_ENABLED") is None
@@ -1341,9 +1357,37 @@ class FlashCausalLM(Model):
                     logger.info, f"Cuda Graphs are enabled for sizes {CUDA_GRAPHS}"
                 )
                 # Warmup cuda graphs
+                last_allocation_amount = 0
+                last_available_memory = free_memory_post_alloc
+                last_bs = 0
                 for bs in CUDA_GRAPHS:
                     if self.speculate is None or self.speculate + 1 <= bs:
+                        expected_memory = int(
+                            last_allocation_amount * (bs / last_bs if last_bs else 2)
+                        )
+                        if expected_memory > last_available_memory:
+                            skipped_graphs = [str(k) for k in CUDA_GRAPHS if k <= bs]
+                            log_master(
+                                logger.warning,
+                                f"Avoiding CUDA graph warmup for sizes {', '.join(skipped_graphs)} due to insufficient memory.",
+                            )
+                            break
+
                         self.cuda_graph_warmup(bs, max_s, max_bt)
+                        current_available_memory = get_free_memory(
+                            self.device, MEMORY_FRACTION
+                        )
+                        last_allocation_amount = (
+                            last_available_memory - current_available_memory
+                        )
+                        last_available_memory = current_available_memory
+                        last_bs = bs
+                # report the total memory used
+                total_cuda_graph_memory = free_memory_post_alloc - last_available_memory
+                log_master(
+                    logger.info,
+                    f"Total memory used for CUDA graphs: {total_cuda_graph_memory/1024/1024:.2f} MB",
+                )
             except torch.cuda.OutOfMemoryError:
                 logger.exception("Decode cuda graph warmup failed")
         else: