runtime: detangle sweeper pacing from GC pacing

The sweeper's pacing state is global, so detangle it from the GC pacer's
state updates so that the GC pacer can be tested.

For #44167.

Change-Id: Ibcea989cd435b73c5891f777d9f95f9604e03bd1
Reviewed-on: https://go-review.googlesource.com/c/go/+/309273
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>

1 files changed, 1 insertions, 34 deletions

diff --git a/src/runtime/mgcpacer.go b/src/runtime/mgcpacer.go
index 73fe6e15e4..980cb2f086 100644
--- a/src/runtime/mgcpacer.go
+++ b/src/runtime/mgcpacer.go
@@ -735,40 +735,6 @@ func (c *gcControllerState) commit(triggerRatio float64) {
 	if gcphase != _GCoff {
 		c.revise()
 	}
-
-	// Update sweep pacing.
-	if isSweepDone() {
-		mheap_.sweepPagesPerByte = 0
-	} else {
-		// Concurrent sweep needs to sweep all of the in-use
-		// pages by the time the allocated heap reaches the GC
-		// trigger. Compute the ratio of in-use pages to sweep
-		// per byte allocated, accounting for the fact that
-		// some might already be swept.
-		heapLiveBasis := atomic.Load64(&c.heapLive)
-		heapDistance := int64(trigger) - int64(heapLiveBasis)
-		// Add a little margin so rounding errors and
-		// concurrent sweep are less likely to leave pages
-		// unswept when GC starts.
-		heapDistance -= 1024 * 1024
-		if heapDistance < _PageSize {
-			// Avoid setting the sweep ratio extremely high
-			heapDistance = _PageSize
-		}
-		pagesSwept := mheap_.pagesSwept.Load()
-		pagesInUse := mheap_.pagesInUse.Load()
-		sweepDistancePages := int64(pagesInUse) - int64(pagesSwept)
-		if sweepDistancePages <= 0 {
-			mheap_.sweepPagesPerByte = 0
-		} else {
-			mheap_.sweepPagesPerByte = float64(sweepDistancePages) / float64(heapDistance)
-			mheap_.sweepHeapLiveBasis = heapLiveBasis
-			// Write pagesSweptBasis last, since this
-			// signals concurrent sweeps to recompute
-			// their debt.
-			mheap_.pagesSweptBasis.Store(pagesSwept)
-		}
-	}
 }
 
 // effectiveGrowthRatio returns the current effective heap growth
@@ -819,6 +785,7 @@ func setGCPercent(in int32) (out int32) {
 	systemstack(func() {
 		lock(&mheap_.lock)
 		out = gcController.setGCPercent(in)
+		gcPaceSweeper(gcController.trigger)
 		gcPaceScavenger(gcController.heapGoal, gcController.lastHeapGoal)
 		unlock(&mheap_.lock)
 	})