runtime: delete hugepage tracking dead code

After the previous CL, this is now all dead code. This change is
separated out to make the previous one easy to backport.

For #63334.
Related to #61718 and #59960.

Change-Id: I109673ed97c62c472bbe2717dfeeb5aa4fc883ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/532117
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/runtime/export_test.go

@@ -1829,10 +1829,6 @@ func (s *ScavengeIndex) SetEmpty(ci ChunkIdx) {
 	s.i.setEmpty(chunkIdx(ci))
 }
 
-func (s *ScavengeIndex) SetNoHugePage(ci ChunkIdx) {
-	s.i.setNoHugePage(chunkIdx(ci))
-}
-
 func CheckPackScavChunkData(gen uint32, inUse, lastInUse uint16, flags uint8) bool {
 	sc0 := scavChunkData{
 		gen:            gen,

src/runtime/mgcscavenge.go

@@ -769,10 +769,6 @@ func (p *pageAlloc) scavengeOne(ci chunkIdx, searchIdx uint, max uintptr) uintpt
 			p.chunkOf(ci).allocRange(base, npages)
 			p.update(addr, uintptr(npages), true, true)
 
-			// Grab whether the chunk is hugepage backed and if it is,
-			// clear it. We're about to break up this huge page.
-			p.scav.index.setNoHugePage(ci)
-
 			// With that done, it's safe to unlock.
 			unlock(p.mheapLock)
 
@@ -1141,16 +1137,11 @@ func (s *scavengeIndex) find(force bool) (chunkIdx, uint) {
 func (s *scavengeIndex) alloc(ci chunkIdx, npages uint) {
 	sc := s.chunks[ci].load()
 	sc.alloc(npages, s.gen)
-	if !sc.isHugePage() && sc.inUse > scavChunkHiOccPages {
+	// TODO(mknyszek): Consider eagerly backing memory with huge pages
-		// Mark that we're considering this chunk as backed by huge pages.
+	// here and track whether we believe this chunk is backed by huge pages.
-		sc.setHugePage()
+	// In the past we've attempted to use sysHugePageCollapse (which uses
-
+	// MADV_COLLAPSE on Linux, and is unsupported elswhere) for this purpose,
-		// TODO(mknyszek): Consider eagerly backing memory with huge pages
+	// but that caused performance issues in production environments.
-		// here. In the past we've attempted to use sysHugePageCollapse
-		// (which uses MADV_COLLAPSE on Linux, and is unsupported elswhere)
-		// for this purpose, but that caused performance issues in production
-		// environments.
-	}
 	s.chunks[ci].store(sc)
 }
 
@@ -1204,19 +1195,6 @@ func (s *scavengeIndex) setEmpty(ci chunkIdx) {
 	s.chunks[ci].store(val)
 }
 
-// setNoHugePage updates the backed-by-hugepages status of a particular chunk.
-// Returns true if the set was successful (not already backed by huge pages).
-//
-// setNoHugePage may only run concurrently with find.
-func (s *scavengeIndex) setNoHugePage(ci chunkIdx) {
-	val := s.chunks[ci].load()
-	if !val.isHugePage() {
-		return
-	}
-	val.setNoHugePage()
-	s.chunks[ci].store(val)
-}
-
 // atomicScavChunkData is an atomic wrapper around a scavChunkData
 // that stores it in its packed form.
 type atomicScavChunkData struct {
@@ -1285,13 +1263,6 @@ const (
 	// file. The reason we say "HasFree" here is so the zero value is
 	// correct for a newly-grown chunk. (New memory is scavenged.)
 	scavChunkHasFree scavChunkFlags = 1 << iota
-	// scavChunkNoHugePage indicates whether this chunk has had any huge
-	// pages broken by the scavenger.
-	//
-	// The negative here is unfortunate, but necessary to make it so that
-	// the zero value of scavChunkData accurately represents the state of
-	// a newly-grown chunk. (New memory is marked as backed by huge pages.)
-	scavChunkNoHugePage
 
 	// scavChunkMaxFlags is the maximum number of flags we can have, given how
 	// a scavChunkData is packed into 8 bytes.
@@ -1324,21 +1295,6 @@ func (sc *scavChunkFlags) setNonEmpty() {
 	*sc |= scavChunkHasFree
 }
 
-// isHugePage returns false if the noHugePage flag is set.
-func (sc *scavChunkFlags) isHugePage() bool {
-	return (*sc)&scavChunkNoHugePage == 0
-}
-
-// setHugePage clears the noHugePage flag.
-func (sc *scavChunkFlags) setHugePage() {
-	*sc &^= scavChunkNoHugePage
-}
-
-// setNoHugePage sets the noHugePage flag.
-func (sc *scavChunkFlags) setNoHugePage() {
-	*sc |= scavChunkNoHugePage
-}
-
 // shouldScavenge returns true if the corresponding chunk should be interrogated
 // by the scavenger.
 func (sc scavChunkData) shouldScavenge(currGen uint32, force bool) bool {