Add start_step to MemorySnapshotProfiler

Summary:
Allows user to configure a `start_step` for when to start recording memory history. Addressing YanjunChen329 's feedback that he would like to record memory history for a specific range of steps, e.g. step 500-503.

Also:
* improve docstrings
* add validation for params
* MemorySnapshot callback no longer needs to call `start` and `stop`

Differential Revision: D51048945

tests/utils/test_memory_snapshot_profiler.py

@@ -35,9 +35,8 @@ def test_stop_step(self) -> None:
         with tempfile.TemporaryDirectory() as temp_dir:
             memory_snapshot_profiler = MemorySnapshotProfiler(
                 output_dir=temp_dir,
-                memory_snapshot_params=MemorySnapshotParams(stop_step=2),
+                memory_snapshot_params=MemorySnapshotParams(start_step=0, stop_step=2),
             )
-            memory_snapshot_profiler.start()
 
             # initialize device & allocate memory for tensors
             device = get_device_from_env()
@@ -64,3 +63,59 @@ def test_stop_step(self) -> None:
             self.assertTrue(os.path.exists(pickle_dump_path))
             self.assertTrue(os.path.exists(trace_path))
             self.assertTrue(os.path.exists(segment_plot_path))
+
+    @unittest.skipUnless(
+        condition=torch_version_geq_2_0,
+        reason="This test needs changes from PyTorch 2.0 to run.",
+    )
+    def test_validation(self) -> None:
+        """Test parameter validation."""
+        with tempfile.TemporaryDirectory() as temp_dir:
+            with self.assertRaisesRegex(ValueError, "start_step must be nonnegative."):
+                _ = MemorySnapshotProfiler(
+                    output_dir=temp_dir,
+                    memory_snapshot_params=MemorySnapshotParams(
+                        start_step=-1, stop_step=0
+                    ),
+                )
+            with self.assertRaisesRegex(
+                ValueError, "stop_step must be specified when start_step is set."
+            ):
+                _ = MemorySnapshotProfiler(
+                    output_dir=temp_dir,
+                    memory_snapshot_params=MemorySnapshotParams(
+                        start_step=2, stop_step=None
+                    ),
+                )
+            with self.assertRaisesRegex(ValueError, "start_step must be < stop_step."):
+                _ = MemorySnapshotProfiler(
+                    output_dir=temp_dir,
+                    memory_snapshot_params=MemorySnapshotParams(
+                        start_step=2, stop_step=0
+                    ),
+                )
+            with self.assertRaisesRegex(ValueError, "stop_step must be positive."):
+                _ = MemorySnapshotProfiler(
+                    output_dir=temp_dir,
+                    memory_snapshot_params=MemorySnapshotParams(stop_step=0),
+                )
+            with self.assertRaisesRegex(
+                ValueError,
+                "stop_step must be enabled with either start_step or enable_oom_observer.",
+            ):
+                _ = MemorySnapshotProfiler(
+                    output_dir=temp_dir,
+                    memory_snapshot_params=MemorySnapshotParams(
+                        stop_step=2, enable_oom_observer=False
+                    ),
+                )
+            with self.assertRaisesRegex(
+                ValueError,
+                "At least one of start_step/stop_step or enable_oom_observer must be set.",
+            ):
+                _ = MemorySnapshotProfiler(
+                    output_dir=temp_dir,
+                    memory_snapshot_params=MemorySnapshotParams(
+                        start_step=None, stop_step=None, enable_oom_observer=False
+                    ),
+                )

torchtnt/framework/callbacks/memory_snapshot.py

@@ -8,7 +8,7 @@
 from typing import Optional
 
 from torchtnt.framework.callback import Callback
-from torchtnt.framework.state import EntryPoint, State
+from torchtnt.framework.state import State
 from torchtnt.framework.unit import TEvalUnit, TPredictUnit, TTrainUnit
 from torchtnt.utils.memory_snapshot_profiler import (
     MemorySnapshotParams,
@@ -42,24 +42,12 @@ def __init__(
         self.memory_snapshot_profiler = MemorySnapshotProfiler(
             output_dir=output_dir, memory_snapshot_params=memory_snapshot_params
         )
-        self.memory_snapshot_profiler.start()
 
     def on_train_step_end(self, state: State, unit: TTrainUnit) -> None:
         self.memory_snapshot_profiler.step()
 
-    def on_train_end(self, state: State, unit: TTrainUnit) -> None:
-        self.memory_snapshot_profiler.stop()
-
     def on_eval_step_end(self, state: State, unit: TEvalUnit) -> None:
         self.memory_snapshot_profiler.step()
 
-    def on_eval_end(self, state: State, unit: TEvalUnit) -> None:
-        # if in fit do nothing since the profiler will be stopped in on_train_end
-        if state.entry_point == EntryPoint.EVALUATE:
-            self.memory_snapshot_profiler.stop()
-
     def on_predict_step_end(self, state: State, unit: TPredictUnit) -> None:
         self.memory_snapshot_profiler.step()
-
-    def on_predict_end(self, state: State, unit: TPredictUnit) -> None:
-        self.memory_snapshot_profiler.stop()

torchtnt/utils/memory_snapshot_profiler.py

@@ -22,12 +22,18 @@ class MemorySnapshotParams:
     Memory snapshot parameters.
 
     Args:
-        stop_step: Number of steps after which to dump memory snapshot, and stop recording memory history.
+        start_step: Step from which to start recording memory history.
+        stop_step: Step after which to dump memory snapshot, and stop recording memory history.
         max_entries: Maximum number of events to keep in memory.
         enable_oom_observer: Whether to attach an observer to record OOM events. If stop_step is set, the
             OOM observer will only be active until stop_step is reached.
+
+    Note: If you set enable_oom_observer to True, you don't necessarily have to set a start_step as attach_oom_observer
+        will start recording memory history. Note that if you don't set a stop_step, it will continue recording memory
+        history until the program exits, which may incur a slight performance cost.
     """
 
+    start_step: Optional[int] = None
     stop_step: Optional[int] = 2
     max_entries: int = 100000
     enable_oom_observer: bool = True
@@ -44,6 +50,20 @@ class MemorySnapshotProfiler:
     Args:
         output_dir: Directory where to save the memory snapshots.
         memory_snapshot_params: Instance of MemorySnapshotParams.
+
+    Raises:
+        ValueError: If `start_step` is negative, or `stop_step` is less than or equal to zero.
+        ValueError: If `start_step` is greater than or equal to `stop_step`.
+        ValueError: If `start_step` is set and `stop_step` is not set.
+        ValueError: If `stop_step` is set and neither `start_step` nor `enable_oom_observer` are set.
+        ValueError: If `enable_oom_observer` is False and neither `start_step` nor `stop_step` is set
+
+    Examples::
+        memory_snapshot_params = MemorySnapshotParams(start_step=5, stop_step=10, enable_oom_observer=True)
+        memory_snapshot_profiler = MemorySnapshotProfiler(output_dir="/tmp", memory_snapshot_params=memory_snapshot_params)
+        for batch in dataloader:
+            ...
+            memory_snapshot_profiler.step()
     """
 
     def __init__(
@@ -55,6 +75,31 @@ def __init__(
         self.params: MemorySnapshotParams = (
             memory_snapshot_params or MemorySnapshotParams()
         )
+        start_step = self.params.start_step
+        stop_step = self.params.stop_step
+        if start_step is not None:
+            if start_step < 0:
+                raise ValueError("start_step must be nonnegative.")
+            elif stop_step is None:
+                raise ValueError("stop_step must be specified when start_step is set.")
+            elif start_step >= stop_step:
+                raise ValueError("start_step must be < stop_step.")
+        if stop_step is not None:
+            if stop_step <= 0:
+                raise ValueError("stop_step must be positive.")
+            elif start_step is None and not self.params.enable_oom_observer:
+                raise ValueError(
+                    "stop_step must be enabled with either start_step or enable_oom_observer."
+                )
+        if (
+            start_step is None
+            and stop_step is None
+            and not self.params.enable_oom_observer
+        ):
+            raise ValueError(
+                "At least one of start_step/stop_step or enable_oom_observer must be set."
+            )
+
         self.step_num: int = 0
 
         if not is_torch_version_geq_2_0():
@@ -63,6 +108,8 @@ def __init__(
             attach_oom_observer(
                 output_dir=output_dir, trace_max_entries=self.params.max_entries
             )
+        if start_step is not None and start_step == 0:
+            self.start()
 
         logger.info(
             f"Created MemorySnapshotProfiler with MemorySnapshotParams={self.params}."
@@ -97,6 +144,11 @@ def stop(self) -> None:
 
     def step(self) -> None:
         self.step_num += 1
+        if (
+            self.params.start_step is not None
+            and self.step_num == self.params.start_step
+        ):
+            self.start()
         if self.params.stop_step is not None and self.step_num == self.params.stop_step:
             log_memory_snapshot(output_dir=self.output_dir)
             self.stop()