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Fix InMemoryCircularBuffer merge failure with large CircularMB #2439

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Fix InMemoryCircularBuffer merge failure with large CircularMB #2439

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8 changes: 7 additions & 1 deletion src/TraceEvent/TraceEventSession.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2509,8 +2509,14 @@ private void EnsureStarted(TraceEventNativeMethods.EVENT_TRACE_PROPERTIES* prope
else
{
properties->LogFileMode |= TraceEventNativeMethods.EVENT_TRACE_BUFFERING_MODE;
// Size the in-memory circular buffer purely by the number of buffers, leaving BufferSize at the
// per-buffer quantum set above (m_BufferQuantumKB). MinimumBuffers is intentionally computed against
// that same quantum so that (MinimumBuffers * BufferSize) == m_CircularBufferMB megabytes.
// Do NOT set BufferSize to m_CircularBufferMB here: BufferSize is a per-buffer size in KB, so treating
// a megabyte value as KB makes each buffer exceed ETW's maximum buffer size. On some systems that
// causes the subsequent KernelTraceControl merge (CreateMergedTraceFile) to fail (e.g. 0x80280012),
// and inflates the requested memory quadratically.
properties->MinimumBuffers = (uint)(m_CircularBufferMB * 1024 / m_BufferQuantumKB);
properties->BufferSize = (uint)m_CircularBufferMB;
}
properties->LogFileNameOffset = 0;
}
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