[release-branch.go1.18] runtime: store consistent total allocation stats as uint64

Currently the consistent total allocation stats are managed as uintptrs,
which means they can easily overflow on 32-bit systems. Fix this by
storing these stats as uint64s. This will cause some minor performance
degradation on 32-bit systems, but there really isn't a way around this,
and it affects the correctness of the metrics we export.

For #52680.
Fixes #52689.

Change-Id: I8b1926116e899ae9f03d58e0320bcb9264945b3e
Reviewed-on: https://go-review.googlesource.com/c/go/+/411495
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/runtime/mcache.go

@@ -175,11 +175,11 @@ func (c *mcache) refill(spc spanClass) {
 	// Assume all objects from this span will be allocated in the
 	// mcache. If it gets uncached, we'll adjust this.
 	stats := memstats.heapStats.acquire()
-	atomic.Xadduintptr(&stats.smallAllocCount[spc.sizeclass()], uintptr(s.nelems)-uintptr(s.allocCount))
+	atomic.Xadd64(&stats.smallAllocCount[spc.sizeclass()], int64(s.nelems)-int64(s.allocCount))
 
 	// Flush tinyAllocs.
 	if spc == tinySpanClass {
-		atomic.Xadduintptr(&stats.tinyAllocCount, c.tinyAllocs)
+		atomic.Xadd64(&stats.tinyAllocCount, int64(c.tinyAllocs))
 		c.tinyAllocs = 0
 	}
 	memstats.heapStats.release()
@@ -215,8 +215,8 @@ func (c *mcache) allocLarge(size uintptr, noscan bool) *mspan {
 		throw("out of memory")
 	}
 	stats := memstats.heapStats.acquire()
-	atomic.Xadduintptr(&stats.largeAlloc, npages*pageSize)
-	atomic.Xadduintptr(&stats.largeAllocCount, 1)
+	atomic.Xadd64(&stats.largeAlloc, int64(npages*pageSize))
+	atomic.Xadd64(&stats.largeAllocCount, 1)
 	memstats.heapStats.release()
 
 	// Update heapLive.
@@ -241,9 +241,9 @@ func (c *mcache) releaseAll() {
 		s := c.alloc[i]
 		if s != &emptymspan {
 			// Adjust nsmallalloc in case the span wasn't fully allocated.
-			n := uintptr(s.nelems) - uintptr(s.allocCount)
+			n := int64(s.nelems) - int64(s.allocCount)
 			stats := memstats.heapStats.acquire()
-			atomic.Xadduintptr(&stats.smallAllocCount[spanClass(i).sizeclass()], -n)
+			atomic.Xadd64(&stats.smallAllocCount[spanClass(i).sizeclass()], -n)
 			memstats.heapStats.release()
 			if s.sweepgen != sg+1 {
 				// refill conservatively counted unallocated slots in gcController.heapLive.
@@ -253,7 +253,7 @@ func (c *mcache) releaseAll() {
 				// gcController.heapLive was totally recomputed since
 				// caching this span, so we don't do this for
 				// stale spans.
-				dHeapLive -= int64(n) * int64(s.elemsize)
+				dHeapLive -= n * int64(s.elemsize)
 			}
 			// Release the span to the mcentral.
 			mheap_.central[i].mcentral.uncacheSpan(s)
@@ -266,7 +266,7 @@ func (c *mcache) releaseAll() {
 
 	// Flush tinyAllocs.
 	stats := memstats.heapStats.acquire()
-	atomic.Xadduintptr(&stats.tinyAllocCount, c.tinyAllocs)
+	atomic.Xadd64(&stats.tinyAllocCount, int64(c.tinyAllocs))
 	c.tinyAllocs = 0
 	memstats.heapStats.release()
 

src/runtime/metrics.go

@@ -388,13 +388,13 @@ func (a *heapStatsAggregate) compute() {
 	memstats.heapStats.read(&a.heapStatsDelta)
 
 	// Calculate derived stats.
-	a.totalAllocs = uint64(a.largeAllocCount)
-	a.totalFrees = uint64(a.largeFreeCount)
-	a.totalAllocated = uint64(a.largeAlloc)
-	a.totalFreed = uint64(a.largeFree)
+	a.totalAllocs = a.largeAllocCount
+	a.totalFrees = a.largeFreeCount
+	a.totalAllocated = a.largeAlloc
+	a.totalFreed = a.largeFree
 	for i := range a.smallAllocCount {
-		na := uint64(a.smallAllocCount[i])
-		nf := uint64(a.smallFreeCount[i])
+		na := a.smallAllocCount[i]
+		nf := a.smallFreeCount[i]
 		a.totalAllocs += na
 		a.totalFrees += nf
 		a.totalAllocated += na * uint64(class_to_size[i])

src/runtime/mgcsweep.go

@@ -666,7 +666,7 @@ func (sl *sweepLocked) sweep(preserve bool) bool {
 			// free slots zeroed.
 			s.needzero = 1
 			stats := memstats.heapStats.acquire()
-			atomic.Xadduintptr(&stats.smallFreeCount[spc.sizeclass()], uintptr(nfreed))
+			atomic.Xadd64(&stats.smallFreeCount[spc.sizeclass()], int64(nfreed))
 			memstats.heapStats.release()
 		}
 		if !preserve {
@@ -713,8 +713,8 @@ func (sl *sweepLocked) sweep(preserve bool) bool {
 				mheap_.freeSpan(s)
 			}
 			stats := memstats.heapStats.acquire()
-			atomic.Xadduintptr(&stats.largeFreeCount, 1)
-			atomic.Xadduintptr(&stats.largeFree, size)
+			atomic.Xadd64(&stats.largeFreeCount, 1)
+			atomic.Xadd64(&stats.largeFree, int64(size))
 			memstats.heapStats.release()
 			return true
 		}

src/runtime/mstats.go

@@ -7,7 +7,6 @@
 package runtime
 
 import (
-	"internal/goarch"
 	"runtime/internal/atomic"
 	"unsafe"
 )
@@ -565,29 +564,29 @@ func updatememstats() {
 	memstats.heapStats.unsafeRead(&consStats)
 
 	// Collect large allocation stats.
-	totalAlloc := uint64(consStats.largeAlloc)
-	memstats.nmalloc += uint64(consStats.largeAllocCount)
-	totalFree := uint64(consStats.largeFree)
-	memstats.nfree += uint64(consStats.largeFreeCount)
+	totalAlloc := consStats.largeAlloc
+	memstats.nmalloc += consStats.largeAllocCount
+	totalFree := consStats.largeFree
+	memstats.nfree += consStats.largeFreeCount
 
 	// Collect per-sizeclass stats.
 	for i := 0; i < _NumSizeClasses; i++ {
 		// Malloc stats.
-		a := uint64(consStats.smallAllocCount[i])
+		a := consStats.smallAllocCount[i]
 		totalAlloc += a * uint64(class_to_size[i])
 		memstats.nmalloc += a
 		memstats.by_size[i].nmalloc = a
 
 		// Free stats.
-		f := uint64(consStats.smallFreeCount[i])
+		f := consStats.smallFreeCount[i]
 		totalFree += f * uint64(class_to_size[i])
 		memstats.nfree += f
 		memstats.by_size[i].nfree = f
 	}
 
 	// Account for tiny allocations.
-	memstats.nfree += uint64(consStats.tinyAllocCount)
-	memstats.nmalloc += uint64(consStats.tinyAllocCount)
+	memstats.nfree += consStats.tinyAllocCount
+	memstats.nmalloc += consStats.tinyAllocCount
 
 	// Calculate derived stats.
 	memstats.total_alloc = totalAlloc
@@ -703,17 +702,20 @@ type heapStatsDelta struct {
 	inPtrScalarBits int64 // byte delta of memory reserved for unrolled GC prog bits
 
 	// Allocator stats.
-	tinyAllocCount  uintptr                  // number of tiny allocations
-	largeAlloc      uintptr                  // bytes allocated for large objects
-	largeAllocCount uintptr                  // number of large object allocations
-	smallAllocCount [_NumSizeClasses]uintptr // number of allocs for small objects
-	largeFree       uintptr                  // bytes freed for large objects (>maxSmallSize)
-	largeFreeCount  uintptr                  // number of frees for large objects (>maxSmallSize)
-	smallFreeCount  [_NumSizeClasses]uintptr // number of frees for small objects (<=maxSmallSize)
+	//
+	// 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)
 
-	// Add a uint32 to ensure this struct is a multiple of 8 bytes in size.
-	// Only necessary on 32-bit platforms.
-	_ [(goarch.PtrSize / 4) % 2]uint32
+	// 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
+	// fields may be unaligned and fail on 32-bit platforms.
 }
 
 // merge adds in the deltas from b into a.