runtime: maintain a direct count of total allocs and frees

This will be used by the memory limit computation to determine
overheads.

For #48409.

Change-Id: Iaa4e26e1e6e46f88d10ba8ebb6b001be876dc5cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/394220
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/runtime/mcache.go

@@ -169,8 +169,12 @@ func (c *mcache) refill(spc spanClass) {
 		}
 		memstats.heapStats.release()
 
+		// Count the allocs in inconsistent, internal stats.
+		bytesAllocated := int64(slotsUsed * s.elemsize)
+		memstats.totalAlloc.Add(bytesAllocated)
+
 		// Update heapLive and flush scanAlloc.
-		gcController.update(int64(slotsUsed*s.elemsize), int64(c.scanAlloc))
+		gcController.update(bytesAllocated, int64(c.scanAlloc))
 		c.scanAlloc = 0
 
 		// Clear the second allocCount just to be safe.
@@ -217,11 +221,16 @@ func (c *mcache) allocLarge(size uintptr, noscan bool) *mspan {
 	if s == nil {
 		throw("out of memory")
 	}
+
+	// Count the alloc in consistent, external stats.
 	stats := memstats.heapStats.acquire()
 	atomic.Xadduintptr(&stats.largeAlloc, npages*pageSize)
 	atomic.Xadduintptr(&stats.largeAllocCount, 1)
 	memstats.heapStats.release()
 
+	// Count the alloc in inconsistent, internal stats.
+	memstats.totalAlloc.Add(int64(npages * pageSize))
+
 	// Update heapLive.
 	gcController.update(int64(s.npages*pageSize), 0)
 
@@ -241,12 +250,17 @@ func (c *mcache) releaseAll() {
 	for i := range c.alloc {
 		s := c.alloc[i]
 		if s != &emptymspan {
+			slotsUsed := uintptr(s.allocCount) - uintptr(s.allocCountBeforeCache)
+			s.allocCountBeforeCache = 0
+
 			// Adjust smallAllocCount for whatever was allocated.
 			stats := memstats.heapStats.acquire()
-			slotsUsed := uintptr(s.allocCount) - uintptr(s.allocCountBeforeCache)
 			atomic.Xadduintptr(&stats.smallAllocCount[spanClass(i).sizeclass()], slotsUsed)
 			memstats.heapStats.release()
-			s.allocCountBeforeCache = 0
+
+			// Adjust the actual allocs in inconsistent, internal stats.
+			// We assumed earlier that the full span gets allocated.
+			memstats.totalAlloc.Add(int64(slotsUsed * s.elemsize))
 
 			// Release the span to the mcentral.
 			mheap_.central[i].mcentral.uncacheSpan(s)

src/runtime/mgcsweep.go

@@ -666,6 +666,9 @@ func (sl *sweepLocked) sweep(preserve bool) bool {
 			stats := memstats.heapStats.acquire()
 			atomic.Xadduintptr(&stats.smallFreeCount[spc.sizeclass()], uintptr(nfreed))
 			memstats.heapStats.release()
+
+			// Count the frees in the inconsistent, internal stats.
+			memstats.totalFree.Add(int64(nfreed) * int64(s.elemsize))
 		}
 		if !preserve {
 			// The caller may not have removed this span from whatever
@@ -710,10 +713,16 @@ func (sl *sweepLocked) sweep(preserve bool) bool {
 			} else {
 				mheap_.freeSpan(s)
 			}
+
+			// Count the free in the consistent, external stats.
 			stats := memstats.heapStats.acquire()
 			atomic.Xadduintptr(&stats.largeFreeCount, 1)
 			atomic.Xadduintptr(&stats.largeFree, size)
 			memstats.heapStats.release()
+
+			// Count the free in the inconsistent, internal stats.
+			memstats.totalFree.Add(int64(size))
+
 			return true
 		}
 

src/runtime/mstats.go

@@ -31,9 +31,11 @@ type mstats struct {
 	//
 	// Like MemStats, heap_sys and heap_inuse do not count memory
 	// in manually-managed spans.
-	heap_sys      sysMemStat // virtual address space obtained from system for GC'd heap
-	heap_inuse    uint64     // bytes in mSpanInUse spans
-	heap_released uint64     // bytes released to the OS
+	heap_sys      sysMemStat    // virtual address space obtained from system for GC'd heap
+	heap_inuse    uint64        // bytes in mSpanInUse spans
+	heap_released uint64        // bytes released to the OS
+	totalAlloc    atomic.Uint64 // total bytes allocated
+	totalFree     atomic.Uint64 // total bytes freed
 
 	// Statistics about stacks.
 	stacks_sys sysMemStat // only counts newosproc0 stack in mstats; differs from MemStats.StackSys
@@ -452,9 +454,11 @@ func readmemstats_m(stats *MemStats) {
 	// The world is stopped, so the consistent stats (after aggregation)
 	// should be identical to some combination of memstats. In particular:
 	//
-	// * heap_inuse == inHeap
-	// * heap_released == released
-	// * heap_sys - heap_released == committed - inStacks - inWorkBufs - inPtrScalarBits
+	// * memstats.heap_inuse == inHeap
+	// * memstats.heap_released == released
+	// * memstats.heap_sys - memstats.heap_released == committed - inStacks - inWorkBufs - inPtrScalarBits
+	// * memstats.totalAlloc == totalAlloc
+	// * memstats.totalFree == totalFree
 	//
 	// Check if that's actually true.
 	//
@@ -478,6 +482,16 @@ func readmemstats_m(stats *MemStats) {
 		print("runtime: consistent value=", consRetained, "\n")
 		throw("measures of the retained heap are not equal")
 	}
+	if memstats.totalAlloc.Load() != totalAlloc {
+		print("runtime: totalAlloc=", memstats.totalAlloc.Load(), "\n")
+		print("runtime: consistent value=", totalAlloc, "\n")
+		throw("totalAlloc and consistent stats are not equal")
+	}
+	if memstats.totalFree.Load() != totalFree {
+		print("runtime: totalFree=", memstats.totalFree.Load(), "\n")
+		print("runtime: consistent value=", totalFree, "\n")
+		throw("totalFree and consistent stats are not equal")
+	}
 
 	// We've calculated all the values we need. Now, populate stats.