runtime: remove go119MemoryLimitSupport flag

Change-Id: I207480d991c6242a1610795605c5ec6a3b3c59de
Reviewed-on: https://go-review.googlesource.com/c/go/+/463225
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/runtime/mgcmark.go

@@ -414,7 +414,7 @@ func gcAssistAlloc(gp *g) {
 
 	traced := false
 retry:
-	if go119MemoryLimitSupport && gcCPULimiter.limiting() {
+	if gcCPULimiter.limiting() {
 		// If the CPU limiter is enabled, intentionally don't
 		// assist to reduce the amount of CPU time spent in the GC.
 		if traced {

src/runtime/mgcpacer.go

@@ -11,12 +11,6 @@ import (
 	_ "unsafe" // for go:linkname
 )
 
-// go119MemoryLimitSupport is a feature flag for a number of changes
-// related to the memory limit feature (#48409). Disabling this flag
-// disables those features, as well as the memory limit mechanism,
-// which becomes a no-op.
-const go119MemoryLimitSupport = true
-
 const (
 	// gcGoalUtilization is the goal CPU utilization for
 	// marking as a fraction of GOMAXPROCS.
@@ -899,7 +893,7 @@ func (c *gcControllerState) heapGoalInternal() (goal, minTrigger uint64) {
 	goal = c.gcPercentHeapGoal.Load()
 
 	// Check if the memory-limit-based goal is smaller, and if so, pick that.
-	if newGoal := c.memoryLimitHeapGoal(); go119MemoryLimitSupport && newGoal < goal {
+	if newGoal := c.memoryLimitHeapGoal(); newGoal < goal {
 		goal = newGoal
 	} else {
 		// We're not limited by the memory limit goal, so perform a series of

src/runtime/mgcscavenge.go

@@ -379,8 +379,7 @@ func (s *scavengerState) init() {
 		s.shouldStop = func() bool {
 			// If background scavenging is disabled or if there's no work to do just stop.
 			return heapRetained() <= scavenge.gcPercentGoal.Load() &&
-				(!go119MemoryLimitSupport ||
+				gcController.mappedReady.Load() <= scavenge.memoryLimitGoal.Load()
-					gcController.mappedReady.Load() <= scavenge.memoryLimitGoal.Load())
 		}
 	}
 	if s.gomaxprocs == nil {

src/runtime/mheap.go

@@ -1270,7 +1270,7 @@ HaveSpan:
 	// pages not to get touched until we return. Simultaneously, it's important
 	// to do this before calling sysUsed because that may commit address space.
 	bytesToScavenge := uintptr(0)
-	if limit := gcController.memoryLimit.Load(); go119MemoryLimitSupport && !gcCPULimiter.limiting() {
+	if limit := gcController.memoryLimit.Load(); !gcCPULimiter.limiting() {
 		// Assist with scavenging to maintain the memory limit by the amount
 		// that we expect to page in.
 		inuse := gcController.mappedReady.Load()

src/runtime/runtime1.go

@@ -364,7 +364,7 @@ func parsedebugvars() {
 	// defaults
 	debug.cgocheck = 1
 	debug.invalidptr = 1
-	debug.adaptivestackstart = 1 // go119 - set this to 0 to turn larger initial goroutine stacks off
+	debug.adaptivestackstart = 1 // set this to 0 to turn larger initial goroutine stacks off
 	if GOOS == "linux" {
 		// On Linux, MADV_FREE is faster than MADV_DONTNEED,
 		// but doesn't affect many of the statistics that