Remove USS sampling from the benchmark memory recorder

source/isaaclab/changelog.d/benchmark-drop-uss-sampling.removed.rst

@@ -0,0 +1,6 @@
+* Removed Unique Set Size (USS) collection from :class:`~isaaclab.benchmark.recorders.MemoryInfoRecorder`.
+  ``psutil.Process.memory_full_info()`` walks the process page tables on every call, and the recorder ran it
+  once per second from the :class:`~isaaclab.benchmark.BenchmarkMonitor` thread while the benchmark was being
+  timed, perturbing the workload being measured. The ``System Memory USS``, ``System Memory USS std``,
+  ``System Memory USS peak`` and ``System Memory USS n`` measurements are no longer emitted. Resident Set Size
+  and Virtual Memory Size are unchanged and are read from cheap kernel counters.

source/isaaclab/isaaclab/benchmark/recorders/record_memory_info.py

@@ -28,16 +28,10 @@ def __init__(self):
         self._vms_m2 = 0
         self._vms_n = 0
 
-        # Welford's algorithm stats for USS (Unique Set Size)
-        self._uss_mean = 0
-        self._uss_m2 = 0
-        self._uss_n = 0
-
         # Peak (running max) alongside the Welford mean/std. Initialised to
         # 0.0 so emit-before-record returns a meaningful zero.
         self._rss_peak = 0.0
         self._vms_peak = 0.0
-        self._uss_peak = 0.0
 
         # Process handle
         self._process = psutil.Process(os.getpid())
@@ -84,20 +78,7 @@ def _get_runtime_info(self) -> None:
         self._memory_runtime_info["vms_n"] = self._vms_n
         self._memory_runtime_info["vms_peak"] = self._vms_peak
 
-        # USS (Unique Set Size) - memory unique to process (not shared)
-        try:
-            uss = self._process.memory_full_info().uss
-            self._uss_mean, self._uss_m2, self._uss_n, uss_std = self._update_welford(
-                uss, self._uss_mean, self._uss_m2, self._uss_n
-            )
-            self._uss_peak = max(self._uss_peak, float(uss))
-            self._memory_runtime_info["uss_mean"] = self._uss_mean
-            self._memory_runtime_info["uss_std"] = uss_std
-            self._memory_runtime_info["uss_n"] = self._uss_n
-            self._memory_runtime_info["uss_peak"] = self._uss_peak
-        except (psutil.AccessDenied, AttributeError):
-            # USS may not be available on all platforms
-            pass
+        # USS (Unique Set Size) is deliberately not sampled, it's too expensive.
 
     def update(self) -> None:
         self._get_runtime_info()
@@ -154,31 +135,6 @@ def get_data(self) -> MeasurementData:
             SingleMeasurement(name="System Memory VMS n", value=self._memory_runtime_info.get("vms_n", 0), unit=""),
         ]
 
-        # USS (Unique Set Size) - only if available
-        if "uss_mean" in self._memory_runtime_info:
-            measurements.extend(
-                [
-                    SingleMeasurement(
-                        name="System Memory USS",
-                        value=self._bytes_to_gb(self._memory_runtime_info.get("uss_mean", 0)),
-                        unit="GB",
-                    ),
-                    SingleMeasurement(
-                        name="System Memory USS std",
-                        value=self._bytes_to_gb(self._memory_runtime_info.get("uss_std", 0)),
-                        unit="GB",
-                    ),
-                    SingleMeasurement(
-                        name="System Memory USS peak",
-                        value=self._bytes_to_gb(self._memory_runtime_info.get("uss_peak", 0)),
-                        unit="GB",
-                    ),
-                    SingleMeasurement(
-                        name="System Memory USS n", value=self._memory_runtime_info.get("uss_n", 0), unit=""
-                    ),
-                ]
-            )
-
         return MeasurementData(
             measurements=measurements,
             metadata=[

source/isaaclab/test/benchmark/test_recorders.py

@@ -257,8 +257,8 @@ def test_get_data_measurement_names(self, recorder):
         assert "System Memory VMS" in names
         assert "System Memory VMS std" in names
         assert "System Memory VMS n" in names
-        # USS measurements may be present depending on platform (mean, std, peak, n)
-        assert 8 <= len(data.measurements) <= 12
+        # Exactly 8: RSS and VMS, each with mean, std, peak and n.
+        assert len(data.measurements) == 8
         metadata = {m.name: m.data for m in data.metadata}
         assert len(data.metadata) == 1
         assert isinstance(metadata["total_ram_gb"], float) and metadata["total_ram_gb"] > 0
@@ -277,7 +277,6 @@ class _FakeMemInfo:
             def __init__(self, rss):
                 self.rss = rss
                 self.vms = rss  # mirror so VMS also moves
-                # USS is read via memory_full_info, not memory_info; leave alone.
 
         def _fake_memory_info(self):  # noqa: ARG001 — bound method, self is the process
             return _FakeMemInfo(next(scripted_iter))