{name: "profstackdepth", value: &debug.profstackdepth, def: 128},
	{name: "runtimecontentionstacks", atomic: &debug.runtimeContentionStacks},
	{name: "sbrk", value: &debug.sbrk},
	{name: "scavtrace", value: &debug.scavtrace},
	{name: "scheddetail", value: &debug.scheddetail},
	{name: "schedtrace", value: &debug.schedtrace},
	{name: "traceadvanceperiod", value: &debug.traceadvanceperiod},

	sbrk: setting sbrk=1 replaces the memory allocator and garbage collector
	with a trivial allocator that obtains memory from the operating system and
	never reclaims any memory.

	scavtrace: setting scavtrace=1 causes the runtime to emit a single line to standard
	error, roughly once per GC cycle, summarizing the amount of work done by the
	scavenger as well as the total amount of memory returned to the operating system

		// between sweep done and sweep termination (e.g. not enough
		// allocations to trigger a GC) which would be nice to fill in
		// with scavenging work.
		if debug.scavtrace > 0 {
			systemstack(func() {
				lock(&mheap_.lock)

				// Get released stats.
				releasedBg := mheap_.pages.scav.releasedBg.Load()
				releasedEager := mheap_.pages.scav.releasedEager.Load()

	// the mheap API.
	gp := getg()
	gp.m.mallocing++

	// Force scavenge everything.
	released := h.pages.scavenge(^uintptr(0), nil, true)

	gp.m.mallocing--

	if debug.scavtrace > 0 {
		printScavTrace(0, released, true)
	}
}

//go:linkname runtime_debug_freeOSMemory runtime/debug.freeOSMemory
func runtime_debug_freeOSMemory() {
	GC()

	Stop()
	size := buf.Len()
	if size == 0 {
		t.Fatalf("trace is empty")
	}
	time.Sleep(100 * time.Millisecond)
	if size != buf.Len() {
		t.Fatalf("trace writes after stop: %v -> %v", size, buf.Len())
	}
	saveTrace(t, buf, "TestTraceStartStop")
}

func TestTraceDoubleStart(t *testing.T) {
	if IsEnabled() {
		t.Skip("skipping because -test.trace is set")
	}
	Stop()
	buf := new(bytes.Buffer)