runtime: move sizeclass defs to new package internal/runtime/gc

We will want to reference these definitions from new generator programs,
and this is a good opportunity to cleanup all these old C-style names.

Change-Id: Ifb06f0afc381e2697e7877f038eca786610c96de
Reviewed-on: https://go-review.googlesource.com/c/go/+/655275
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

17 files changed, 110 insertions, 98 deletions

diff --git a/src/cmd/internal/objabi/pkgspecial.go b/src/cmd/internal/objabi/pkgspecial.go
index 118d2d4126..55b66b6055 100644
--- a/src/cmd/internal/objabi/pkgspecial.go
+++ b/src/cmd/internal/objabi/pkgspecial.go
@@ -50,6 +50,7 @@ var runtimePkgs = []string{
 
 	"internal/runtime/atomic",
 	"internal/runtime/exithook",
+	"internal/runtime/gc",
 	"internal/runtime/maps",
 	"internal/runtime/math",
 	"internal/runtime/sys",
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 21bf8b76a5..1eb683a5ae 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -94,6 +94,7 @@ var depsRules = `
 	< internal/runtime/syscall
 	< internal/runtime/atomic
 	< internal/runtime/exithook
+	< internal/runtime/gc
 	< internal/runtime/math
 	< internal/runtime/maps
 	< runtime
diff --git a/src/runtime/mksizeclasses.go b/src/internal/runtime/gc/mksizeclasses.go
index bb06ba1edd..ea48cda469 100644
--- a/src/runtime/mksizeclasses.go
+++ b/src/internal/runtime/gc/mksizeclasses.go
@@ -289,29 +289,29 @@ func maxObjsPerSpan(classes []class) int {
 
 func printClasses(w io.Writer, classes []class) {
 	fmt.Fprintln(w, "const (")
-	fmt.Fprintf(w, "minHeapAlign = %d\n", minHeapAlign)
-	fmt.Fprintf(w, "_MaxSmallSize = %d\n", maxSmallSize)
-	fmt.Fprintf(w, "smallSizeDiv = %d\n", smallSizeDiv)
-	fmt.Fprintf(w, "smallSizeMax = %d\n", smallSizeMax)
-	fmt.Fprintf(w, "largeSizeDiv = %d\n", largeSizeDiv)
-	fmt.Fprintf(w, "_NumSizeClasses = %d\n", len(classes))
-	fmt.Fprintf(w, "_PageShift = %d\n", pageShift)
-	fmt.Fprintf(w, "maxObjsPerSpan = %d\n", maxObjsPerSpan(classes))
+	fmt.Fprintf(w, "MinHeapAlign = %d\n", minHeapAlign)
+	fmt.Fprintf(w, "MaxSmallSize = %d\n", maxSmallSize)
+	fmt.Fprintf(w, "SmallSizeDiv = %d\n", smallSizeDiv)
+	fmt.Fprintf(w, "SmallSizeMax = %d\n", smallSizeMax)
+	fmt.Fprintf(w, "LargeSizeDiv = %d\n", largeSizeDiv)
+	fmt.Fprintf(w, "NumSizeClasses = %d\n", len(classes))
+	fmt.Fprintf(w, "PageShift = %d\n", pageShift)
+	fmt.Fprintf(w, "MaxObjsPerSpan = %d\n", maxObjsPerSpan(classes))
 	fmt.Fprintln(w, ")")
 
-	fmt.Fprint(w, "var class_to_size = [_NumSizeClasses]uint16 {")
+	fmt.Fprint(w, "var SizeClassToSize = [NumSizeClasses]uint16 {")
 	for _, c := range classes {
 		fmt.Fprintf(w, "%d,", c.size)
 	}
 	fmt.Fprintln(w, "}")
 
-	fmt.Fprint(w, "var class_to_allocnpages = [_NumSizeClasses]uint8 {")
+	fmt.Fprint(w, "var SizeClassToNPages = [NumSizeClasses]uint8 {")
 	for _, c := range classes {
 		fmt.Fprintf(w, "%d,", c.npages)
 	}
 	fmt.Fprintln(w, "}")
 
-	fmt.Fprint(w, "var class_to_divmagic = [_NumSizeClasses]uint32 {")
+	fmt.Fprint(w, "var SizeClassToDivMagic = [NumSizeClasses]uint32 {")
 	for _, c := range classes {
 		if c.size == 0 {
 			fmt.Fprintf(w, "0,")
@@ -332,7 +332,7 @@ func printClasses(w io.Writer, classes []class) {
 			}
 		}
 	}
-	fmt.Fprint(w, "var size_to_class8 = [smallSizeMax/smallSizeDiv+1]uint8 {")
+	fmt.Fprint(w, "var SizeToSizeClass8 = [SmallSizeMax/SmallSizeDiv+1]uint8 {")
 	for _, v := range sc {
 		fmt.Fprintf(w, "%d,", v)
 	}
@@ -349,7 +349,7 @@ func printClasses(w io.Writer, classes []class) {
 			}
 		}
 	}
-	fmt.Fprint(w, "var size_to_class128 = [(_MaxSmallSize-smallSizeMax)/largeSizeDiv+1]uint8 {")
+	fmt.Fprint(w, "var SizeToSizeClass128 = [(MaxSmallSize-SmallSizeMax)/LargeSizeDiv+1]uint8 {")
 	for _, v := range sc {
 		fmt.Fprintf(w, "%d,", v)
 	}
diff --git a/src/runtime/sizeclasses.go b/src/internal/runtime/gc/sizeclasses.go
index bbcaa9e983..d2cca1cef1 100644
--- a/src/runtime/sizeclasses.go
+++ b/src/internal/runtime/gc/sizeclasses.go
@@ -1,7 +1,7 @@
 // Code generated by mksizeclasses.go; DO NOT EDIT.
 //go:generate go run mksizeclasses.go
 
-package runtime
+package gc
 
 // class  bytes/obj  bytes/span  objects  tail waste  max waste  min align
 //     1          8        8192     1024           0     87.50%          8
@@ -82,18 +82,18 @@ package runtime
 //      8192    13         32768
 
 const (
-	minHeapAlign    = 8
-	_MaxSmallSize   = 32768
-	smallSizeDiv    = 8
-	smallSizeMax    = 1024
-	largeSizeDiv    = 128
-	_NumSizeClasses = 68
-	_PageShift      = 13
-	maxObjsPerSpan  = 1024
+	MinHeapAlign   = 8
+	MaxSmallSize   = 32768
+	SmallSizeDiv   = 8
+	SmallSizeMax   = 1024
+	LargeSizeDiv   = 128
+	NumSizeClasses = 68
+	PageShift      = 13
+	MaxObjsPerSpan = 1024
 )
 
-var class_to_size = [_NumSizeClasses]uint16{0, 8, 16, 24, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, 240, 256, 288, 320, 352, 384, 416, 448, 480, 512, 576, 640, 704, 768, 896, 1024, 1152, 1280, 1408, 1536, 1792, 2048, 2304, 2688, 3072, 3200, 3456, 4096, 4864, 5376, 6144, 6528, 6784, 6912, 8192, 9472, 9728, 10240, 10880, 12288, 13568, 14336, 16384, 18432, 19072, 20480, 21760, 24576, 27264, 28672, 32768}
-var class_to_allocnpages = [_NumSizeClasses]uint8{0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 3, 2, 3, 1, 3, 2, 3, 4, 5, 6, 1, 7, 6, 5, 4, 3, 5, 7, 2, 9, 7, 5, 8, 3, 10, 7, 4}
-var class_to_divmagic = [_NumSizeClasses]uint32{0, ^uint32(0)/8 + 1, ^uint32(0)/16 + 1, ^uint32(0)/24 + 1, ^uint32(0)/32 + 1, ^uint32(0)/48 + 1, ^uint32(0)/64 + 1, ^uint32(0)/80 + 1, ^uint32(0)/96 + 1, ^uint32(0)/112 + 1, ^uint32(0)/128 + 1, ^uint32(0)/144 + 1, ^uint32(0)/160 + 1, ^uint32(0)/176 + 1, ^uint32(0)/192 + 1, ^uint32(0)/208 + 1, ^uint32(0)/224 + 1, ^uint32(0)/240 + 1, ^uint32(0)/256 + 1, ^uint32(0)/288 + 1, ^uint32(0)/320 + 1, ^uint32(0)/352 + 1, ^uint32(0)/384 + 1, ^uint32(0)/416 + 1, ^uint32(0)/448 + 1, ^uint32(0)/480 + 1, ^uint32(0)/512 + 1, ^uint32(0)/576 + 1, ^uint32(0)/640 + 1, ^uint32(0)/704 + 1, ^uint32(0)/768 + 1, ^uint32(0)/896 + 1, ^uint32(0)/1024 + 1, ^uint32(0)/1152 + 1, ^uint32(0)/1280 + 1, ^uint32(0)/1408 + 1, ^uint32(0)/1536 + 1, ^uint32(0)/1792 + 1, ^uint32(0)/2048 + 1, ^uint32(0)/2304 + 1, ^uint32(0)/2688 + 1, ^uint32(0)/3072 + 1, ^uint32(0)/3200 + 1, ^uint32(0)/3456 + 1, ^uint32(0)/4096 + 1, ^uint32(0)/4864 + 1, ^uint32(0)/5376 + 1, ^uint32(0)/6144 + 1, ^uint32(0)/6528 + 1, ^uint32(0)/6784 + 1, ^uint32(0)/6912 + 1, ^uint32(0)/8192 + 1, ^uint32(0)/9472 + 1, ^uint32(0)/9728 + 1, ^uint32(0)/10240 + 1, ^uint32(0)/10880 + 1, ^uint32(0)/12288 + 1, ^uint32(0)/13568 + 1, ^uint32(0)/14336 + 1, ^uint32(0)/16384 + 1, ^uint32(0)/18432 + 1, ^uint32(0)/19072 + 1, ^uint32(0)/20480 + 1, ^uint32(0)/21760 + 1, ^uint32(0)/24576 + 1, ^uint32(0)/27264 + 1, ^uint32(0)/28672 + 1, ^uint32(0)/32768 + 1}
-var size_to_class8 = [smallSizeMax/smallSizeDiv + 1]uint8{0, 1, 2, 3, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 22, 22, 22, 22, 23, 23, 23, 23, 24, 24, 24, 24, 25, 25, 25, 25, 26, 26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27, 28, 28, 28, 28, 28, 28, 28, 28, 29, 29, 29, 29, 29, 29, 29, 29, 30, 30, 30, 30, 30, 30, 30, 30, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32}
-var size_to_class128 = [(_MaxSmallSize-smallSizeMax)/largeSizeDiv + 1]uint8{32, 33, 34, 35, 36, 37, 37, 38, 38, 39, 39, 40, 40, 40, 41, 41, 41, 42, 43, 43, 44, 44, 44, 44, 44, 45, 45, 45, 45, 45, 45, 46, 46, 46, 46, 47, 47, 47, 47, 47, 47, 48, 48, 48, 49, 49, 50, 51, 51, 51, 51, 51, 51, 51, 51, 51, 51, 52, 52, 52, 52, 52, 52, 52, 52, 52, 52, 53, 53, 54, 54, 54, 54, 55, 55, 55, 55, 55, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 57, 57, 57, 57, 57, 57, 57, 57, 57, 57, 58, 58, 58, 58, 58, 58, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 61, 61, 61, 61, 61, 62, 62, 62, 62, 62, 62, 62, 62, 62, 62, 62, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 66, 66, 66, 66, 66, 66, 66, 66, 66, 66, 66, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67}
+var SizeClassToSize = [NumSizeClasses]uint16{0, 8, 16, 24, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, 240, 256, 288, 320, 352, 384, 416, 448, 480, 512, 576, 640, 704, 768, 896, 1024, 1152, 1280, 1408, 1536, 1792, 2048, 2304, 2688, 3072, 3200, 3456, 4096, 4864, 5376, 6144, 6528, 6784, 6912, 8192, 9472, 9728, 10240, 10880, 12288, 13568, 14336, 16384, 18432, 19072, 20480, 21760, 24576, 27264, 28672, 32768}
+var SizeClassToNPages = [NumSizeClasses]uint8{0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 3, 2, 3, 1, 3, 2, 3, 4, 5, 6, 1, 7, 6, 5, 4, 3, 5, 7, 2, 9, 7, 5, 8, 3, 10, 7, 4}
+var SizeClassToDivMagic = [NumSizeClasses]uint32{0, ^uint32(0)/8 + 1, ^uint32(0)/16 + 1, ^uint32(0)/24 + 1, ^uint32(0)/32 + 1, ^uint32(0)/48 + 1, ^uint32(0)/64 + 1, ^uint32(0)/80 + 1, ^uint32(0)/96 + 1, ^uint32(0)/112 + 1, ^uint32(0)/128 + 1, ^uint32(0)/144 + 1, ^uint32(0)/160 + 1, ^uint32(0)/176 + 1, ^uint32(0)/192 + 1, ^uint32(0)/208 + 1, ^uint32(0)/224 + 1, ^uint32(0)/240 + 1, ^uint32(0)/256 + 1, ^uint32(0)/288 + 1, ^uint32(0)/320 + 1, ^uint32(0)/352 + 1, ^uint32(0)/384 + 1, ^uint32(0)/416 + 1, ^uint32(0)/448 + 1, ^uint32(0)/480 + 1, ^uint32(0)/512 + 1, ^uint32(0)/576 + 1, ^uint32(0)/640 + 1, ^uint32(0)/704 + 1, ^uint32(0)/768 + 1, ^uint32(0)/896 + 1, ^uint32(0)/1024 + 1, ^uint32(0)/1152 + 1, ^uint32(0)/1280 + 1, ^uint32(0)/1408 + 1, ^uint32(0)/1536 + 1, ^uint32(0)/1792 + 1, ^uint32(0)/2048 + 1, ^uint32(0)/2304 + 1, ^uint32(0)/2688 + 1, ^uint32(0)/3072 + 1, ^uint32(0)/3200 + 1, ^uint32(0)/3456 + 1, ^uint32(0)/4096 + 1, ^uint32(0)/4864 + 1, ^uint32(0)/5376 + 1, ^uint32(0)/6144 + 1, ^uint32(0)/6528 + 1, ^uint32(0)/6784 + 1, ^uint32(0)/6912 + 1, ^uint32(0)/8192 + 1, ^uint32(0)/9472 + 1, ^uint32(0)/9728 + 1, ^uint32(0)/10240 + 1, ^uint32(0)/10880 + 1, ^uint32(0)/12288 + 1, ^uint32(0)/13568 + 1, ^uint32(0)/14336 + 1, ^uint32(0)/16384 + 1, ^uint32(0)/18432 + 1, ^uint32(0)/19072 + 1, ^uint32(0)/20480 + 1, ^uint32(0)/21760 + 1, ^uint32(0)/24576 + 1, ^uint32(0)/27264 + 1, ^uint32(0)/28672 + 1, ^uint32(0)/32768 + 1}
+var SizeToSizeClass8 = [SmallSizeMax/SmallSizeDiv + 1]uint8{0, 1, 2, 3, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 22, 22, 22, 22, 23, 23, 23, 23, 24, 24, 24, 24, 25, 25, 25, 25, 26, 26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27, 28, 28, 28, 28, 28, 28, 28, 28, 29, 29, 29, 29, 29, 29, 29, 29, 30, 30, 30, 30, 30, 30, 30, 30, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 31, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32, 32}
+var SizeToSizeClass128 = [(MaxSmallSize-SmallSizeMax)/LargeSizeDiv + 1]uint8{32, 33, 34, 35, 36, 37, 37, 38, 38, 39, 39, 40, 40, 40, 41, 41, 41, 42, 43, 43, 44, 44, 44, 44, 44, 45, 45, 45, 45, 45, 45, 46, 46, 46, 46, 47, 47, 47, 47, 47, 47, 48, 48, 48, 49, 49, 50, 51, 51, 51, 51, 51, 51, 51, 51, 51, 51, 52, 52, 52, 52, 52, 52, 52, 52, 52, 52, 53, 53, 54, 54, 54, 54, 55, 55, 55, 55, 55, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 57, 57, 57, 57, 57, 57, 57, 57, 57, 57, 58, 58, 58, 58, 58, 58, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 61, 61, 61, 61, 61, 62, 62, 62, 62, 62, 62, 62, 62, 62, 62, 62, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 65, 66, 66, 66, 66, 66, 66, 66, 66, 66, 66, 66, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67, 67}
diff --git a/src/runtime/export_test.go b/src/runtime/export_test.go
index 8da4ece881..572f62c2f9 100644
--- a/src/runtime/export_test.go
+++ b/src/runtime/export_test.go
@@ -11,6 +11,7 @@ import (
 	"internal/goarch"
 	"internal/goos"
 	"internal/runtime/atomic"
+	"internal/runtime/gc"
 	"internal/runtime/sys"
 	"unsafe"
 )
@@ -363,7 +364,7 @@ func ReadMemStatsSlow() (base, slow MemStats) {
 		slow.Mallocs = 0
 		slow.Frees = 0
 		slow.HeapReleased = 0
-		var bySize [_NumSizeClasses]struct {
+		var bySize [gc.NumSizeClasses]struct {
 			Mallocs, Frees uint64
 		}
 
@@ -391,11 +392,11 @@ func ReadMemStatsSlow() (base, slow MemStats) {
 
 		// Collect per-sizeclass free stats.
 		var smallFree uint64
-		for i := 0; i < _NumSizeClasses; i++ {
+		for i := 0; i < gc.NumSizeClasses; i++ {
 			slow.Frees += m.smallFreeCount[i]
 			bySize[i].Frees += m.smallFreeCount[i]
 			bySize[i].Mallocs += m.smallFreeCount[i]
-			smallFree += m.smallFreeCount[i] * uint64(class_to_size[i])
+			smallFree += m.smallFreeCount[i] * uint64(gc.SizeClassToSize[i])
 		}
 		slow.Frees += m.tinyAllocCount + m.largeFreeCount
 		slow.Mallocs += slow.Frees
diff --git a/src/runtime/heapdump.go b/src/runtime/heapdump.go
index 6287cccd5f..6e6b58edd5 100644
--- a/src/runtime/heapdump.go
+++ b/src/runtime/heapdump.go
@@ -14,6 +14,7 @@ package runtime
 import (
 	"internal/abi"
 	"internal/goarch"
+	"internal/runtime/gc"
 	"unsafe"
 )
 
@@ -471,7 +472,7 @@ func dumproots() {
 
 // Bit vector of free marks.
 // Needs to be as big as the largest number of objects per span.
-var freemark [_PageSize / 8]bool
+var freemark [pageSize / 8]bool
 
 func dumpobjs() {
 	// To protect mheap_.allspans.
@@ -483,7 +484,7 @@ func dumpobjs() {
 		}
 		p := s.base()
 		size := s.elemsize
-		n := (s.npages << _PageShift) / size
+		n := (s.npages << gc.PageShift) / size
 		if n > uintptr(len(freemark)) {
 			throw("freemark array doesn't have enough entries")
 		}
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index 0a48f8bc61..554cfa6fcf 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -104,6 +104,7 @@ import (
 	"internal/goarch"
 	"internal/goos"
 	"internal/runtime/atomic"
+	"internal/runtime/gc"
 	"internal/runtime/math"
 	"internal/runtime/sys"
 	"unsafe"
@@ -112,13 +113,10 @@ import (
 const (
 	maxTinySize   = _TinySize
 	tinySizeClass = _TinySizeClass
-	maxSmallSize  = _MaxSmallSize
-
-	pageShift = _PageShift
-	pageSize  = _PageSize
-
-	_PageSize = 1 << _PageShift
-	_PageMask = _PageSize - 1
+	maxSmallSize  = gc.MaxSmallSize
+	pageSize      = 1 << gc.PageShift
+	pageMask      = pageSize - 1
+	_PageSize     = pageSize // Unused. Left for viewcore.
 
 	// _64bit = 1 on 64-bit systems, 0 on 32-bit systems
 	_64bit = 1 << (^uintptr(0) >> 63) / 2
@@ -371,7 +369,7 @@ var (
 )
 
 func mallocinit() {
-	if class_to_size[_TinySizeClass] != _TinySize {
+	if gc.SizeClassToSize[tinySizeClass] != maxTinySize {
 		throw("bad TinySizeClass")
 	}
 
@@ -432,11 +430,11 @@ func mallocinit() {
 	// span sizes are one page. Some code relies on this.
 	minSizeForMallocHeaderIsSizeClass := false
 	sizeClassesUpToMinSizeForMallocHeaderAreOnePage := true
-	for i := 0; i < len(class_to_size); i++ {
-		if class_to_allocnpages[i] > 1 {
+	for i := 0; i < len(gc.SizeClassToSize); i++ {
+		if gc.SizeClassToNPages[i] > 1 {
 			sizeClassesUpToMinSizeForMallocHeaderAreOnePage = false
 		}
-		if minSizeForMallocHeader == uintptr(class_to_size[i]) {
+		if minSizeForMallocHeader == uintptr(gc.SizeClassToSize[i]) {
 			minSizeForMallocHeaderIsSizeClass = true
 			break
 		}
@@ -1272,12 +1270,12 @@ func mallocgcSmallNoscan(size uintptr, typ *_type, needzero bool) (unsafe.Pointe
 	checkGCTrigger := false
 	c := getMCache(mp)
 	var sizeclass uint8
-	if size <= smallSizeMax-8 {
-		sizeclass = size_to_class8[divRoundUp(size, smallSizeDiv)]
+	if size <= gc.SmallSizeMax-8 {
+		sizeclass = gc.SizeToSizeClass8[divRoundUp(size, gc.SmallSizeDiv)]
 	} else {
-		sizeclass = size_to_class128[divRoundUp(size-smallSizeMax, largeSizeDiv)]
+		sizeclass = gc.SizeToSizeClass128[divRoundUp(size-gc.SmallSizeMax, gc.LargeSizeDiv)]
 	}
-	size = uintptr(class_to_size[sizeclass])
+	size = uintptr(gc.SizeClassToSize[sizeclass])
 	spc := makeSpanClass(sizeclass, true)
 	span := c.alloc[spc]
 	v := nextFreeFast(span)
@@ -1360,7 +1358,7 @@ func mallocgcSmallScanNoHeader(size uintptr, typ *_type) (unsafe.Pointer, uintpt
 
 	checkGCTrigger := false
 	c := getMCache(mp)
-	sizeclass := size_to_class8[divRoundUp(size, smallSizeDiv)]
+	sizeclass := gc.SizeToSizeClass8[divRoundUp(size, gc.SmallSizeDiv)]
 	spc := makeSpanClass(sizeclass, false)
 	span := c.alloc[spc]
 	v := nextFreeFast(span)
@@ -1378,7 +1376,7 @@ func mallocgcSmallScanNoHeader(size uintptr, typ *_type) (unsafe.Pointer, uintpt
 	} else {
 		c.scanAlloc += heapSetTypeNoHeader(uintptr(x), size, typ, span)
 	}
-	size = uintptr(class_to_size[sizeclass])
+	size = uintptr(gc.SizeClassToSize[sizeclass])
 
 	// Ensure that the stores above that initialize x to
 	// type-safe memory and set the heap bits occur before
@@ -1453,12 +1451,12 @@ func mallocgcSmallScanHeader(size uintptr, typ *_type) (unsafe.Pointer, uintptr)
 	c := getMCache(mp)
 	size += mallocHeaderSize
 	var sizeclass uint8
-	if size <= smallSizeMax-8 {
-		sizeclass = size_to_class8[divRoundUp(size, smallSizeDiv)]
+	if size <= gc.SmallSizeMax-8 {
+		sizeclass = gc.SizeToSizeClass8[divRoundUp(size, gc.SmallSizeDiv)]
 	} else {
-		sizeclass = size_to_class128[divRoundUp(size-smallSizeMax, largeSizeDiv)]
+		sizeclass = gc.SizeToSizeClass128[divRoundUp(size-gc.SmallSizeMax, gc.LargeSizeDiv)]
 	}
-	size = uintptr(class_to_size[sizeclass])
+	size = uintptr(gc.SizeClassToSize[sizeclass])
 	spc := makeSpanClass(sizeclass, false)
 	span := c.alloc[spc]
 	v := nextFreeFast(span)
@@ -1909,7 +1907,7 @@ func persistentalloc1(size, align uintptr, sysStat *sysMemStat) *notInHeap {
 		if align&(align-1) != 0 {
 			throw("persistentalloc: align is not a power of 2")
 		}
-		if align > _PageSize {
+		if align > pageSize {
 			throw("persistentalloc: align is too large")
 		}
 	} else {
diff --git a/src/runtime/mcache.go b/src/runtime/mcache.go
index 44d737b19c..440120cdfe 100644
--- a/src/runtime/mcache.go
+++ b/src/runtime/mcache.go
@@ -6,6 +6,7 @@ package runtime
 
 import (
 	"internal/runtime/atomic"
+	"internal/runtime/gc"
 	"internal/runtime/sys"
 	"unsafe"
 )
@@ -218,18 +219,18 @@ func (c *mcache) refill(spc spanClass) {
 
 // allocLarge allocates a span for a large object.
 func (c *mcache) allocLarge(size uintptr, noscan bool) *mspan {
-	if size+_PageSize < size {
+	if size+pageSize < size {
 		throw("out of memory")
 	}
-	npages := size >> _PageShift
-	if size&_PageMask != 0 {
+	npages := size >> gc.PageShift
+	if size&pageMask != 0 {
 		npages++
 	}
 
 	// Deduct credit for this span allocation and sweep if
 	// necessary. mHeap_Alloc will also sweep npages, so this only
 	// pays the debt down to npage pages.
-	deductSweepCredit(npages*_PageSize, npages)
+	deductSweepCredit(npages*pageSize, npages)
 
 	spc := makeSpanClass(0, noscan)
 	s := mheap_.alloc(npages, spc)
diff --git a/src/runtime/mcentral.go b/src/runtime/mcentral.go
index 08ff0a5c5d..21731f3fec 100644
--- a/src/runtime/mcentral.go
+++ b/src/runtime/mcentral.go
@@ -14,6 +14,7 @@ package runtime
 
 import (
 	"internal/runtime/atomic"
+	"internal/runtime/gc"
 	"internal/runtime/sys"
 )
 
@@ -80,7 +81,7 @@ func (c *mcentral) fullSwept(sweepgen uint32) *spanSet {
 // Allocate a span to use in an mcache.
 func (c *mcentral) cacheSpan() *mspan {
 	// Deduct credit for this span allocation and sweep if necessary.
-	spanBytes := uintptr(class_to_allocnpages[c.spanclass.sizeclass()]) * _PageSize
+	spanBytes := uintptr(gc.SizeClassToNPages[c.spanclass.sizeclass()]) * pageSize
 	deductSweepCredit(spanBytes, 0)
 
 	traceDone := false
@@ -248,8 +249,8 @@ func (c *mcentral) uncacheSpan(s *mspan) {
 
 // grow allocates a new empty span from the heap and initializes it for c's size class.
 func (c *mcentral) grow() *mspan {
-	npages := uintptr(class_to_allocnpages[c.spanclass.sizeclass()])
-	size := uintptr(class_to_size[c.spanclass.sizeclass()])
+	npages := uintptr(gc.SizeClassToNPages[c.spanclass.sizeclass()])
+	size := uintptr(gc.SizeClassToSize[c.spanclass.sizeclass()])
 
 	s := mheap_.alloc(npages, c.spanclass)
 	if s == nil {
@@ -257,8 +258,8 @@ func (c *mcentral) grow() *mspan {
 	}
 
 	// Use division by multiplication and shifts to quickly compute:
-	// n := (npages << _PageShift) / size
-	n := s.divideByElemSize(npages << _PageShift)
+	// n := (npages << gc.PageShift) / size
+	n := s.divideByElemSize(npages << gc.PageShift)
 	s.limit = s.base() + size*n
 	s.initHeapBits()
 	return s
diff --git a/src/runtime/metrics.go b/src/runtime/metrics.go
index 417f1071bb..949a2d42bd 100644
--- a/src/runtime/metrics.go
+++ b/src/runtime/metrics.go
@@ -8,6 +8,7 @@ package runtime
 
 import (
 	"internal/godebugs"
+	"internal/runtime/gc"
 	"unsafe"
 )
 
@@ -62,12 +63,12 @@ func initMetrics() {
 		return
 	}
 
-	sizeClassBuckets = make([]float64, _NumSizeClasses, _NumSizeClasses+1)
+	sizeClassBuckets = make([]float64, gc.NumSizeClasses, gc.NumSizeClasses+1)
 	// Skip size class 0 which is a stand-in for large objects, but large
 	// objects are tracked separately (and they actually get placed in
 	// the last bucket, not the first).
 	sizeClassBuckets[0] = 1 // The smallest allocation is 1 byte in size.
-	for i := 1; i < _NumSizeClasses; i++ {
+	for i := 1; i < gc.NumSizeClasses; i++ {
 		// Size classes have an inclusive upper-bound
 		// and exclusive lower bound (e.g. 48-byte size class is
 		// (32, 48]) whereas we want and inclusive lower-bound
@@ -79,7 +80,7 @@ func initMetrics() {
 		// value up to 2^53 and size classes are relatively small
 		// (nowhere near 2^48 even) so this will give us exact
 		// boundaries.
-		sizeClassBuckets[i] = float64(class_to_size[i] + 1)
+		sizeClassBuckets[i] = float64(gc.SizeClassToSize[i] + 1)
 	}
 	sizeClassBuckets = append(sizeClassBuckets, float64Inf())
 
@@ -615,8 +616,8 @@ func (a *heapStatsAggregate) compute() {
 		nf := a.smallFreeCount[i]
 		a.totalAllocs += na
 		a.totalFrees += nf
-		a.totalAllocated += na * uint64(class_to_size[i])
-		a.totalFreed += nf * uint64(class_to_size[i])
+		a.totalAllocated += na * uint64(gc.SizeClassToSize[i])
+		a.totalFreed += nf * uint64(gc.SizeClassToSize[i])
 	}
 	a.inObjects = a.totalAllocated - a.totalFreed
 	a.numObjects = a.totalAllocs - a.totalFrees
diff --git a/src/runtime/mgcsweep.go b/src/runtime/mgcsweep.go
index b6890bac47..4fd80a6883 100644
--- a/src/runtime/mgcsweep.go
+++ b/src/runtime/mgcsweep.go
@@ -517,7 +517,7 @@ func (sl *sweepLocked) sweep(preserve bool) bool {
 
 	trace := traceAcquire()
 	if trace.ok() {
-		trace.GCSweepSpan(s.npages * _PageSize)
+		trace.GCSweepSpan(s.npages * pageSize)
 		traceRelease(trace)
 	}
 
@@ -981,9 +981,9 @@ func gcPaceSweeper(trigger uint64) {
 		// concurrent sweep are less likely to leave pages
 		// unswept when GC starts.
 		heapDistance -= 1024 * 1024
-		if heapDistance < _PageSize {
+		if heapDistance < pageSize {
 			// Avoid setting the sweep ratio extremely high
-			heapDistance = _PageSize
+			heapDistance = pageSize
 		}
 		pagesSwept := mheap_.pagesSwept.Load()
 		pagesInUse := mheap_.pagesInUse.Load()
diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index 50ff68646f..7e6c284423 100644
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -13,6 +13,7 @@ import (
 	"internal/cpu"
 	"internal/goarch"
 	"internal/runtime/atomic"
+	"internal/runtime/gc"
 	"internal/runtime/sys"
 	"unsafe"
 )
@@ -514,7 +515,7 @@ func (s *mspan) base() uintptr {
 }
 
 func (s *mspan) layout() (size, n, total uintptr) {
-	total = s.npages << _PageShift
+	total = s.npages << gc.PageShift
 	size = s.elemsize
 	if size > 0 {
 		n = total / size
@@ -576,7 +577,7 @@ func recordspan(vh unsafe.Pointer, p unsafe.Pointer) {
 type spanClass uint8
 
 const (
-	numSpanClasses = _NumSizeClasses << 1
+	numSpanClasses = gc.NumSizeClasses << 1
 	tinySpanClass  = spanClass(tinySizeClass<<1 | 1)
 )
 
@@ -1423,14 +1424,14 @@ func (h *mheap) initSpan(s *mspan, typ spanAllocType, spanclass spanClass, base,
 			s.nelems = 1
 			s.divMul = 0
 		} else {
-			s.elemsize = uintptr(class_to_size[sizeclass])
+			s.elemsize = uintptr(gc.SizeClassToSize[sizeclass])
 			if !s.spanclass.noscan() && heapBitsInSpan(s.elemsize) {
 				// Reserve space for the pointer/scan bitmap at the end.
 				s.nelems = uint16((nbytes - (nbytes / goarch.PtrSize / 8)) / s.elemsize)
 			} else {
 				s.nelems = uint16(nbytes / s.elemsize)
 			}
-			s.divMul = class_to_divmagic[sizeclass]
+			s.divMul = gc.SizeClassToDivMagic[sizeclass]
 		}
 
 		// Initialize mark and allocation structures.
@@ -1589,13 +1590,13 @@ func (h *mheap) freeSpan(s *mspan) {
 		if msanenabled {
 			// Tell msan that this entire span is no longer in use.
 			base := unsafe.Pointer(s.base())
-			bytes := s.npages << _PageShift
+			bytes := s.npages << gc.PageShift
 			msanfree(base, bytes)
 		}
 		if asanenabled {
 			// Tell asan that this entire span is no longer in use.
 			base := unsafe.Pointer(s.base())
-			bytes := s.npages << _PageShift
+			bytes := s.npages << gc.PageShift
 			asanpoison(base, bytes)
 		}
 		h.freeSpanLocked(s, spanAllocHeap)
diff --git a/src/runtime/mpagealloc.go b/src/runtime/mpagealloc.go
index c9491e31f4..4c58fb6e02 100644
--- a/src/runtime/mpagealloc.go
+++ b/src/runtime/mpagealloc.go
@@ -49,6 +49,7 @@ package runtime
 
 import (
 	"internal/runtime/atomic"
+	"internal/runtime/gc"
 	"unsafe"
 )
 
@@ -58,7 +59,7 @@ const (
 	pallocChunkPages    = 1 << logPallocChunkPages
 	pallocChunkBytes    = pallocChunkPages * pageSize
 	logPallocChunkPages = 9
-	logPallocChunkBytes = logPallocChunkPages + pageShift
+	logPallocChunkBytes = logPallocChunkPages + gc.PageShift
 
 	// The number of radix bits for each level.
 	//
diff --git a/src/runtime/msize.go b/src/runtime/msize.go
index 64d1531ab0..428a86e5aa 100644
--- a/src/runtime/msize.go
+++ b/src/runtime/msize.go
@@ -9,6 +9,8 @@
 
 package runtime
 
+import "internal/runtime/gc"
+
 // Returns size of the memory block that mallocgc will allocate if you ask for the size,
 // minus any inline space for metadata.
 func roundupsize(size uintptr, noscan bool) (reqSize uintptr) {
@@ -20,10 +22,10 @@ func roundupsize(size uintptr, noscan bool) (reqSize uintptr) {
 		}
 		// (reqSize - size) is either mallocHeaderSize or 0. We need to subtract mallocHeaderSize
 		// from the result if we have one, since mallocgc will add it back in.
-		if reqSize <= smallSizeMax-8 {
-			return uintptr(class_to_size[size_to_class8[divRoundUp(reqSize, smallSizeDiv)]]) - (reqSize - size)
+		if reqSize <= gc.SmallSizeMax-8 {
+			return uintptr(gc.SizeClassToSize[gc.SizeToSizeClass8[divRoundUp(reqSize, gc.SmallSizeDiv)]]) - (reqSize - size)
 		}
-		return uintptr(class_to_size[size_to_class128[divRoundUp(reqSize-smallSizeMax, largeSizeDiv)]]) - (reqSize - size)
+		return uintptr(gc.SizeClassToSize[gc.SizeToSizeClass128[divRoundUp(reqSize-gc.SmallSizeMax, gc.LargeSizeDiv)]]) - (reqSize - size)
 	}
 	// Large object. Align reqSize up to the next page. Check for overflow.
 	reqSize += pageSize - 1
diff --git a/src/runtime/mstats.go b/src/runtime/mstats.go
index 888798c600..ea61385998 100644
--- a/src/runtime/mstats.go
+++ b/src/runtime/mstats.go
@@ -8,6 +8,7 @@ package runtime
 
 import (
 	"internal/runtime/atomic"
+	"internal/runtime/gc"
 	"unsafe"
 )
 
@@ -397,23 +398,23 @@ func readmemstats_m(stats *MemStats) {
 	nFree := consStats.largeFreeCount
 
 	// Collect per-sizeclass stats.
-	var bySize [_NumSizeClasses]struct {
+	var bySize [gc.NumSizeClasses]struct {
 		Size    uint32
 		Mallocs uint64
 		Frees   uint64
 	}
 	for i := range bySize {
-		bySize[i].Size = uint32(class_to_size[i])
+		bySize[i].Size = uint32(gc.SizeClassToSize[i])
 
 		// Malloc stats.
 		a := consStats.smallAllocCount[i]
-		totalAlloc += a * uint64(class_to_size[i])
+		totalAlloc += a * uint64(gc.SizeClassToSize[i])
 		nMalloc += a
 		bySize[i].Mallocs = a
 
 		// Free stats.
 		f := consStats.smallFreeCount[i]
-		totalFree += f * uint64(class_to_size[i])
+		totalFree += f * uint64(gc.SizeClassToSize[i])
 		nFree += f
 		bySize[i].Frees = f
 	}
@@ -678,13 +679,13 @@ type heapStatsDelta struct {
 	//
 	// These are all uint64 because they're cumulative, and could quickly wrap
 	// around otherwise.
-	tinyAllocCount  uint64                  // number of tiny allocations
-	largeAlloc      uint64                  // bytes allocated for large objects
-	largeAllocCount uint64                  // number of large object allocations
-	smallAllocCount [_NumSizeClasses]uint64 // number of allocs for small objects
-	largeFree       uint64                  // bytes freed for large objects (>maxSmallSize)
-	largeFreeCount  uint64                  // number of frees for large objects (>maxSmallSize)
-	smallFreeCount  [_NumSizeClasses]uint64 // number of frees for small objects (<=maxSmallSize)
+	tinyAllocCount  uint64                    // number of tiny allocations
+	largeAlloc      uint64                    // bytes allocated for large objects
+	largeAllocCount uint64                    // number of large object allocations
+	smallAllocCount [gc.NumSizeClasses]uint64 // number of allocs for small objects
+	largeFree       uint64                    // bytes freed for large objects (>maxSmallSize)
+	largeFreeCount  uint64                    // number of frees for large objects (>maxSmallSize)
+	smallFreeCount  [gc.NumSizeClasses]uint64 // number of frees for small objects (<=maxSmallSize)
 
 	// NOTE: This struct must be a multiple of 8 bytes in size because it
 	// is stored in an array. If it's not, atomic accesses to the above
diff --git a/src/runtime/stack.go b/src/runtime/stack.go
index a2866322a9..2fedaa9421 100644
--- a/src/runtime/stack.go
+++ b/src/runtime/stack.go
@@ -10,6 +10,7 @@ import (
 	"internal/goarch"
 	"internal/goos"
 	"internal/runtime/atomic"
+	"internal/runtime/gc"
 	"internal/runtime/sys"
 	"unsafe"
 )
@@ -161,11 +162,11 @@ type stackpoolItem struct {
 // Global pool of large stack spans.
 var stackLarge struct {
 	lock mutex
-	free [heapAddrBits - pageShift]mSpanList // free lists by log_2(s.npages)
+	free [heapAddrBits - gc.PageShift]mSpanList // free lists by log_2(s.npages)
 }
 
 func stackinit() {
-	if _StackCacheSize&_PageMask != 0 {
+	if _StackCacheSize&pageMask != 0 {
 		throw("cache size must be a multiple of page size")
 	}
 	for i := range stackpool {
@@ -196,7 +197,7 @@ func stackpoolalloc(order uint8) gclinkptr {
 	lockWithRankMayAcquire(&mheap_.lock, lockRankMheap)
 	if s == nil {
 		// no free stacks. Allocate another span worth.
-		s = mheap_.allocManual(_StackCacheSize>>_PageShift, spanAllocStack)
+		s = mheap_.allocManual(_StackCacheSize>>gc.PageShift, spanAllocStack)
 		if s == nil {
 			throw("out of memory")
 		}
@@ -390,7 +391,7 @@ func stackalloc(n uint32) stack {
 		v = unsafe.Pointer(x)
 	} else {
 		var s *mspan
-		npage := uintptr(n) >> _PageShift
+		npage := uintptr(n) >> gc.PageShift
 		log2npage := stacklog2(npage)
 
 		// Try to get a stack from the large stack cache.
diff --git a/src/runtime/traceallocfree.go b/src/runtime/traceallocfree.go
index 40f1cfe8ab..70e48ea3a6 100644
--- a/src/runtime/traceallocfree.go
+++ b/src/runtime/traceallocfree.go
@@ -8,6 +8,7 @@ package runtime
 
 import (
 	"internal/abi"
+	"internal/runtime/gc"
 	"internal/runtime/sys"
 	"internal/trace/tracev2"
 )
@@ -38,7 +39,7 @@ func traceSnapshotMemory(gen uintptr) {
 	// Emit info.
 	w.varint(uint64(trace.minPageHeapAddr))
 	w.varint(uint64(pageSize))
-	w.varint(uint64(minHeapAlign))
+	w.varint(uint64(gc.MinHeapAlign))
 	w.varint(uint64(fixedStack))
 
 	// Finish writing the batch.
@@ -129,7 +130,7 @@ func (tl traceLocker) HeapObjectFree(addr uintptr) {
 
 // traceHeapObjectID creates a trace ID for a heap object at address addr.
 func traceHeapObjectID(addr uintptr) traceArg {
-	return traceArg(uint64(addr)-trace.minPageHeapAddr) / minHeapAlign
+	return traceArg(uint64(addr)-trace.minPageHeapAddr) / gc.MinHeapAlign
 }
 
 // GoroutineStackExists records that a goroutine stack already exists at address base with the provided size.