runtime: track scannable globals space

For #44167.

Change-Id: I2cd13229d88f630451fabd113b0e5a04841e9e79
Reviewed-on: https://go-review.googlesource.com/c/go/+/309590
Trust: Michael Knyszek <[email protected]>
Run-TryBot: Michael Knyszek <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>

Author: mknyszek

src/runtime/mgcpacer.go

@@ -182,6 +182,12 @@ type gcControllerState struct {
 	// Read and updated atomically.
 	scannableStackSize uint64
 
+	// globalsScan is the total amount of global variable space
+	// that is scannable.
+	//
+	// Read and updated atomically.
+	globalsScan uint64
+
 	// heapMarked is the number of bytes marked by the previous
 	// GC. After mark termination, heapLive == heapMarked, but
 	// unlike heapLive, heapMarked does not change until the
@@ -715,6 +721,10 @@ func (c *gcControllerState) addScannableStack(pp *p, amount int64) {
 	}
 }
 
+func (c *gcControllerState) addGlobals(amount int64) {
+	atomic.Xadd64(&c.globalsScan, amount)
+}
+
 // commit sets the trigger ratio and updates everything
 // derived from it: the absolute trigger, the heap goal, mark pacing,
 // and sweep pacing.

src/runtime/symtab.go

@@ -529,8 +529,11 @@ func modulesinit() {
 		}
 		*modules = append(*modules, md)
 		if md.gcdatamask == (bitvector{}) {
-			md.gcdatamask = progToPointerMask((*byte)(unsafe.Pointer(md.gcdata)), md.edata-md.data)
-			md.gcbssmask = progToPointerMask((*byte)(unsafe.Pointer(md.gcbss)), md.ebss-md.bss)
+			scanDataSize := md.edata - md.data
+			md.gcdatamask = progToPointerMask((*byte)(unsafe.Pointer(md.gcdata)), scanDataSize)
+			scanBSSSize := md.ebss - md.bss
+			md.gcbssmask = progToPointerMask((*byte)(unsafe.Pointer(md.gcbss)), scanBSSSize)
+			gcController.addGlobals(int64(scanDataSize + scanBSSSize))
 		}
 	}