feat(display): cap malloc arenas in-process and malloc_trim between screens (#774)

* feat(display): cap malloc arenas in-process and malloc_trim between screens Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * test: malloc_tuning with ctypes mocked; add to the mypy ratchet Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * docs(changelog): malloc arena cap and malloc_trim between screens Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> * docs(changelog): spacing Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-05 14:55:08 +00:00 · 2026-10-05 10:47:29 -04:00
parent a669d781f5
commit e745ae8060
6 changed files with 366 additions and 0 deletions
@@ -0,0 +1,206 @@
+"""src/malloc_tuning.py: glibc arena cap and periodic malloc_trim, ctypes mocked."""
+import ctypes
+from pathlib import Path
+from unittest import mock
+
+import pytest
+
+from src import malloc_tuning as mt
+
+
+class FakeLibc:
+    """Stands in for ctypes.CDLL(None) on glibc: records calls."""
+
+    def __init__(self, trim_result=1, glibc=True):
+        self.trims = []
+        self.mallopts = []
+        self._trim_result = trim_result
+        if glibc:
+            self.gnu_get_libc_version = lambda: b'2.41'
+        self.malloc_trim = mock.Mock(side_effect=self._trim)
+        self.mallopt = mock.Mock(side_effect=self._mallopt)
+
+    def _trim(self, pad):
+        self.trims.append(pad)
+        if isinstance(self._trim_result, Exception):
+            raise self._trim_result
+        return self._trim_result
+
+    def _mallopt(self, param, value):
+        self.mallopts.append((param, value))
+        return 1
+
+
+@pytest.fixture(autouse=True)
+def fresh_libc(monkeypatch):
+    """Each test loads the C library itself; nothing real is called."""
+    monkeypatch.setattr(mt, '_libc', mt._UNLOADED)
+    monkeypatch.delenv('MALLOC_ARENA_MAX', raising=False)
+    yield
+
+
+def _on_glibc(monkeypatch, libc):
+    monkeypatch.setattr(mt.sys, 'platform', 'linux')
+    cdll = mock.Mock(return_value=libc)
+    monkeypatch.setattr(mt.ctypes, 'CDLL', cdll)
+    return cdll
+
+
+class Clock:
+    def __init__(self, t=1000.0):
+        self.t = t
+
+    def __call__(self):
+        return self.t
+
+
+# -- loading ----------------------------------------------------------------
+
+@pytest.mark.parametrize('platform', ['win32', 'darwin', 'freebsd14'])
+def test_not_linux_loads_nothing(monkeypatch, platform):
+    monkeypatch.setattr(mt.sys, 'platform', platform)
+    cdll = mock.Mock(side_effect=AssertionError('must not load'))
+    monkeypatch.setattr(mt.ctypes, 'CDLL', cdll)
+    assert mt._load_libc() is None
+    assert mt.cap_arenas() is False
+    trimmer = mt.MallocTrimmer(interval=0)
+    assert not trimmer.available
+    assert trimmer.maybe_trim() is False
+    cdll.assert_not_called()
+
+
+def test_linux_without_glibc_is_a_noop(monkeypatch):
+    """musl: no gnu_get_libc_version (and no malloc_trim) -- nothing is called."""
+    libc = FakeLibc(glibc=False)
+    del libc.malloc_trim
+    _on_glibc(monkeypatch, libc)
+    assert mt._load_libc() is None
+    assert mt.cap_arenas() is False
+    assert mt.MallocTrimmer(interval=0).maybe_trim() is False
+    assert libc.mallopts == []
+
+
+def test_cdll_failure_is_a_noop(monkeypatch):
+    monkeypatch.setattr(mt.sys, 'platform', 'linux')
+    monkeypatch.setattr(mt.ctypes, 'CDLL', mock.Mock(side_effect=OSError('no libc')))
+    assert mt._load_libc() is None
+    assert mt.cap_arenas() is False
+
+
+def test_loads_once(monkeypatch):
+    cdll = _on_glibc(monkeypatch, FakeLibc())
+    mt._load_libc()
+    mt._load_libc()
+    mt.MallocTrimmer()
+    assert cdll.call_count == 1
+
+
+def test_declares_c_signatures(monkeypatch):
+    libc = FakeLibc()
+    _on_glibc(monkeypatch, libc)
+    mt._load_libc()
+    assert libc.malloc_trim.argtypes == [ctypes.c_size_t]
+    assert libc.mallopt.argtypes == [ctypes.c_int, ctypes.c_int]
+
+
+# -- cap_arenas ---------------------------------------------------------------
+
+def test_cap_arenas_calls_mallopt(monkeypatch):
+    libc = FakeLibc()
+    _on_glibc(monkeypatch, libc)
+    assert mt.cap_arenas() is True
+    assert libc.mallopts == [(mt.M_ARENA_MAX, 2)]
+    assert mt.M_ARENA_MAX == -8  # glibc's malloc.h
+
+
+def test_cap_arenas_defers_to_the_environment(monkeypatch):
+    libc = FakeLibc()
+    _on_glibc(monkeypatch, libc)
+    monkeypatch.setenv('MALLOC_ARENA_MAX', '4')
+    assert mt.cap_arenas() is False
+    assert libc.mallopts == []
+
+
+def test_cap_arenas_swallows_errors(monkeypatch):
+    libc = FakeLibc()
+    libc.mallopt = mock.Mock(side_effect=RuntimeError('boom'))
+    _on_glibc(monkeypatch, libc)
+    assert mt.cap_arenas() is False
+
+
+def test_cap_arenas_matches_the_unit():
+    """The in-process default is the value the unit's MALLOC_ARENA_MAX carries."""
+    unit = (Path(__file__).resolve().parent.parent / 'systemd' / 'ledmatrix.service').read_text()
+    assert f'Environment=MALLOC_ARENA_MAX={mt.DEFAULT_ARENA_MAX}\n' in unit
+
+
+# -- MallocTrimmer ------------------------------------------------------------
+
+def test_trim_waits_one_interval_then_rate_limits(monkeypatch):
+    libc = FakeLibc()
+    _on_glibc(monkeypatch, libc)
+    clock = Clock()
+    trimmer = mt.MallocTrimmer(interval=300, clock=clock)
+    assert trimmer.available
+    assert trimmer.maybe_trim() is False          # start-up: not yet
+    clock.t += 299.9
+    assert trimmer.maybe_trim() is False
+    clock.t += 0.1
+    assert trimmer.maybe_trim() is True
+    assert libc.trims == [0]
+    clock.t += 100
+    assert trimmer.maybe_trim() is False          # rate-limited
+    clock.t += 200
+    assert trimmer.maybe_trim() is True
+    assert libc.trims == [0, 0]
+
+
+def test_trim_reports_nothing_released(monkeypatch):
+    libc = FakeLibc(trim_result=0)
+    _on_glibc(monkeypatch, libc)
+    clock = Clock()
+    trimmer = mt.MallocTrimmer(interval=10, clock=clock)
+    clock.t += 10
+    assert trimmer.maybe_trim() is False
+    assert libc.trims == [0]
+
+
+def test_trim_failure_disables_trimming(monkeypatch):
+    libc = FakeLibc(trim_result=RuntimeError('boom'))
+    _on_glibc(monkeypatch, libc)
+    clock = Clock()
+    trimmer = mt.MallocTrimmer(interval=10, clock=clock)
+    clock.t += 10
+    assert trimmer.maybe_trim() is False
+    clock.t += 10
+    assert trimmer.maybe_trim() is False
+    assert libc.trims == [0]                      # not retried
+    assert not trimmer.available
+
+
+# -- wiring -------------------------------------------------------------------
+
+def test_run_py_caps_arenas_before_threads():
+    """run.py applies the cap before the watchdog or the controller import."""
+    src = (Path(__file__).resolve().parent.parent / 'run.py').read_text()
+    cap = src.index('malloc_tuning.cap_arenas()')
+    assert cap < src.index('display_watchdog.watchdog.begin_startup()')
+    assert cap < src.index('from src.display_controller import main')
+
+
+def test_render_loop_trims_between_screens():
+    src = (Path(__file__).resolve().parent.parent / 'src' / 'display_controller.py').read_text()
+    loop = src.index('display_watchdog.watchdog.loop_pass()')
+    trim = src.index('trimmer.maybe_trim()')
+    assert loop < trim < src.index('outcome = runner.run(plan, manager_to_display)')
+
+
+@pytest.mark.skipif(not mt.sys.platform.startswith('linux'), reason='glibc only')
+def test_real_libc_on_linux():
+    """On a real Linux C library the calls go through without raising."""
+    if mt._load_libc() is None:
+        pytest.skip('not glibc')
+    trimmer = mt.MallocTrimmer(interval=0)
+    assert trimmer.available
+    assert trimmer.maybe_trim() in (True, False)
+    assert trimmer.available  # did not fail and disable itself