runtime: remove unused gcstats

The gcstats structure is no longer consumed by anything and no longer
tracks statistics that are particularly relevant to the concurrent
garbage collector. Remove it. (Having statistics is probably a good
idea, but these aren't the stats we need these days and we don't have
a way to get them out of the runtime.)

In preparation for #13613.

Change-Id: Ib63e2f9067850668f9dcbfd4ed89aab4a6622c3f
Reviewed-on: https://go-review.googlesource.com/34936
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Rick Hudson <rlh@golang.org>

src/runtime/heapdump.go

@@ -653,7 +653,7 @@ func writeheapdump_m(fd uintptr) {
 	// Update stats so we can dump them.
 	// As a side effect, flushes all the MCaches so the MSpan.freelist
 	// lists contain all the free objects.
-	updatememstats(nil)
+	updatememstats()
 
 	// Set dump file.
 	dumpfd = fd

src/runtime/mgcwork.go

@@ -397,15 +397,11 @@ func getfull() *workbuf {
 		if work.nwait == work.nproc && work.markrootNext >= work.markrootJobs {
 			return nil
 		}
-		_g_ := getg()
 		if i < 10 {
-			_g_.m.gcstats.nprocyield++
 			procyield(20)
 		} else if i < 20 {
-			_g_.m.gcstats.nosyield++
 			osyield()
 		} else {
-			_g_.m.gcstats.nsleep++
 			usleep(100)
 		}
 	}
@@ -419,9 +415,6 @@ func handoff(b *workbuf) *workbuf {
 	b.nobj -= n
 	b1.nobj = n
 	memmove(unsafe.Pointer(&b1.obj[0]), unsafe.Pointer(&b.obj[b.nobj]), uintptr(n)*unsafe.Sizeof(b1.obj[0]))
-	_g_ := getg()
-	_g_.m.gcstats.nhandoff++
-	_g_.m.gcstats.nhandoffcnt += uint64(n)
 
 	// Put b on full list - let first half of b get stolen.
 	putfull(b)

src/runtime/mstats.go

@@ -452,7 +452,7 @@ func ReadMemStats(m *MemStats) {
 }
 
 func readmemstats_m(stats *MemStats) {
-	updatememstats(nil)
+	updatememstats()
 
 	// The size of the trailing by_size array differs between
 	// mstats and MemStats. NumSizeClasses was changed, but we
@@ -506,21 +506,7 @@ func readGCStats_m(pauses *[]uint64) {
 }
 
 //go:nowritebarrier
-func updatememstats(stats *gcstats) {
-	if stats != nil {
-		*stats = gcstats{}
-	}
-	for mp := allm; mp != nil; mp = mp.alllink {
-		if stats != nil {
-			src := (*[unsafe.Sizeof(gcstats{}) / 8]uint64)(unsafe.Pointer(&mp.gcstats))
-			dst := (*[unsafe.Sizeof(gcstats{}) / 8]uint64)(unsafe.Pointer(stats))
-			for i, v := range src {
-				dst[i] += v
-			}
-			mp.gcstats = gcstats{}
-		}
-	}
-
+func updatememstats() {
 	memstats.mcache_inuse = uint64(mheap_.cachealloc.inuse)
 	memstats.mspan_inuse = uint64(mheap_.spanalloc.inuse)
 	memstats.sys = memstats.heap_sys + memstats.stacks_sys + memstats.mspan_sys +

src/runtime/runtime2.go

@@ -292,16 +292,6 @@ type sudog struct {
 	c           *hchan // channel
 }
 
-type gcstats struct {
-	// the struct must consist of only uint64's,
-	// because it is casted to uint64[].
-	nhandoff    uint64
-	nhandoffcnt uint64
-	nprocyield  uint64
-	nosyield    uint64
-	nsleep      uint64
-}
-
 type libcall struct {
 	fn   uintptr
 	n    uintptr // number of parameters
@@ -436,7 +426,6 @@ type m struct {
 	fflag         uint32      // floating point compare flags
 	locked        uint32      // tracking for lockosthread
 	nextwaitm     uintptr     // next m waiting for lock
-	gcstats       gcstats
 	needextram    bool
 	traceback     uint8
 	waitunlockf   unsafe.Pointer // todo go func(*g, unsafe.pointer) bool