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GH-4109: report the top three RSS growths, and stop calling them retainers #4144

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Merged
jeremydmiller merged 1 commit into from
Aug 26, 2026
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GH-4109: report the top three RSS growths, and stop calling them retainers #4144

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24 changes: 20 additions & 4 deletions build/SupervisedTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -291,14 +291,30 @@ bool report(string projectName, string framework, SupervisorResults results, boo
Log.Warning(" [STALLED] {Test} — {Seconds}s in flight on lane {Lane}",
stalled.DisplayName, (int)stalled.InFlight.TotalSeconds, stalled.Worker.Lane);

// GH-4109. Report the top THREE, and do not call them retainers.
//
// This is a start-to-verdict RSS delta, which is heap EXPANSION, not live bytes: the GC does
// not hand memory back to the OS promptly, so whichever test happens to be running when the
// heap grows is charged for all of it. Naming a single winner "top retainer" reads as an
// accusation against that test, and the very first measurement this ever produced sent us
// after CoreTests.Acceptance.wolverine_as_command_bus.use_iasync_enumerable_as_return_value
// at +685 MB -- a test that sends three empty records and awaits two 50ms delays.
//
// Five consecutive runs of the same unchanged suite named five DIFFERENT tests (+535 MB to
// +1084 MB) while peak RSS stayed flat at 4956-5468 MB. The leader is noise; the peak is the
// signal. Three entries make that visible in the log itself -- a test that really does retain
// will hold its place across runs, and a run whose three entries are all strangers is telling
// you the ranking means nothing this time.
var memory = RunResources.For(results);
if (memory.IsMeasured)
{
Log.Information(" peak worker RSS {Peak}; top retainer: {Retainer}",
var growth = memory.TopRetainers(3)
.Select(x => $"{RunResources.Delta(x.RetainedBytes!.Value)} {x.DisplayName}")
.ToArray();

Log.Information(" peak worker RSS {Peak}; largest RSS growth during: {Growth}",
RunResources.Humanize(memory.PeakBytes!.Value),
memory.TopRetainers(1) is [{ } top]
? $"{RunResources.Delta(top.RetainedBytes!.Value)} {top.DisplayName}"
: "(none attributed)");
growth.Length > 0 ? string.Join(", ", growth) : "(none attributed)");
}

foreach (var test in results.Indeterminate)
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