Adding upstream version 1.18.10.upstream/1.18.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 928 insertions, 0 deletions

diff --git a/src/runtime/mstats.go b/src/runtime/mstats.go
new file mode 100644
index 0000000..2c1ec79
--- /dev/null
+++ b/src/runtime/mstats.go
@@ -0,0 +1,928 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Memory statistics
+
+package runtime
+
+import (
+	"runtime/internal/atomic"
+	"unsafe"
+)
+
+// Statistics.
+//
+// For detailed descriptions see the documentation for MemStats.
+// Fields that differ from MemStats are further documented here.
+//
+// Many of these fields are updated on the fly, while others are only
+// updated when updatememstats is called.
+type mstats struct {
+	// General statistics.
+	alloc       uint64 // bytes allocated and not yet freed
+	total_alloc uint64 // bytes allocated (even if freed)
+	sys         uint64 // bytes obtained from system (should be sum of xxx_sys below, no locking, approximate)
+	nlookup     uint64 // number of pointer lookups (unused)
+	nmalloc     uint64 // number of mallocs
+	nfree       uint64 // number of frees
+
+	// Statistics about malloc heap.
+	// Updated atomically, or with the world stopped.
+	//
+	// 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_objects is not used by the runtime directly and instead
+	// computed on the fly by updatememstats.
+	heap_objects uint64 // total number of allocated objects
+
+	// Statistics about stacks.
+	stacks_inuse uint64     // bytes in manually-managed stack spans; computed by updatememstats
+	stacks_sys   sysMemStat // only counts newosproc0 stack in mstats; differs from MemStats.StackSys
+
+	// Statistics about allocation of low-level fixed-size structures.
+	// Protected by FixAlloc locks.
+	mspan_inuse  uint64 // mspan structures
+	mspan_sys    sysMemStat
+	mcache_inuse uint64 // mcache structures
+	mcache_sys   sysMemStat
+	buckhash_sys sysMemStat // profiling bucket hash table
+
+	// Statistics about GC overhead.
+	gcWorkBufInUse           uint64     // computed by updatememstats
+	gcProgPtrScalarBitsInUse uint64     // computed by updatememstats
+	gcMiscSys                sysMemStat // updated atomically or during STW
+
+	// Miscellaneous statistics.
+	other_sys sysMemStat // updated atomically or during STW
+
+	// Statistics about the garbage collector.
+
+	// Protected by mheap or stopping the world during GC.
+	last_gc_unix    uint64 // last gc (in unix time)
+	pause_total_ns  uint64
+	pause_ns        [256]uint64 // circular buffer of recent gc pause lengths
+	pause_end       [256]uint64 // circular buffer of recent gc end times (nanoseconds since 1970)
+	numgc           uint32
+	numforcedgc     uint32  // number of user-forced GCs
+	gc_cpu_fraction float64 // fraction of CPU time used by GC
+	enablegc        bool
+	debuggc         bool
+
+	// Statistics about allocation size classes.
+
+	by_size [_NumSizeClasses]struct {
+		size    uint32
+		nmalloc uint64
+		nfree   uint64
+	}
+
+	// Add an uint32 for even number of size classes to align below fields
+	// to 64 bits for atomic operations on 32 bit platforms.
+	_ [1 - _NumSizeClasses%2]uint32
+
+	last_gc_nanotime uint64 // last gc (monotonic time)
+	last_heap_inuse  uint64 // heap_inuse at mark termination of the previous GC
+
+	// heapStats is a set of statistics
+	heapStats consistentHeapStats
+
+	// _ uint32 // ensure gcPauseDist is aligned
+
+	// gcPauseDist represents the distribution of all GC-related
+	// application pauses in the runtime.
+	//
+	// Each individual pause is counted separately, unlike pause_ns.
+	gcPauseDist timeHistogram
+}
+
+var memstats mstats
+
+// A MemStats records statistics about the memory allocator.
+type MemStats struct {
+	// General statistics.
+
+	// Alloc is bytes of allocated heap objects.
+	//
+	// This is the same as HeapAlloc (see below).
+	Alloc uint64
+
+	// TotalAlloc is cumulative bytes allocated for heap objects.
+	//
+	// TotalAlloc increases as heap objects are allocated, but
+	// unlike Alloc and HeapAlloc, it does not decrease when
+	// objects are freed.
+	TotalAlloc uint64
+
+	// Sys is the total bytes of memory obtained from the OS.
+	//
+	// Sys is the sum of the XSys fields below. Sys measures the
+	// virtual address space reserved by the Go runtime for the
+	// heap, stacks, and other internal data structures. It's
+	// likely that not all of the virtual address space is backed
+	// by physical memory at any given moment, though in general
+	// it all was at some point.
+	Sys uint64
+
+	// Lookups is the number of pointer lookups performed by the
+	// runtime.
+	//
+	// This is primarily useful for debugging runtime internals.
+	Lookups uint64
+
+	// Mallocs is the cumulative count of heap objects allocated.
+	// The number of live objects is Mallocs - Frees.
+	Mallocs uint64
+
+	// Frees is the cumulative count of heap objects freed.
+	Frees uint64
+
+	// Heap memory statistics.
+	//
+	// Interpreting the heap statistics requires some knowledge of
+	// how Go organizes memory. Go divides the virtual address
+	// space of the heap into "spans", which are contiguous
+	// regions of memory 8K or larger. A span may be in one of
+	// three states:
+	//
+	// An "idle" span contains no objects or other data. The
+	// physical memory backing an idle span can be released back
+	// to the OS (but the virtual address space never is), or it
+	// can be converted into an "in use" or "stack" span.
+	//
+	// An "in use" span contains at least one heap object and may
+	// have free space available to allocate more heap objects.
+	//
+	// A "stack" span is used for goroutine stacks. Stack spans
+	// are not considered part of the heap. A span can change
+	// between heap and stack memory; it is never used for both
+	// simultaneously.
+
+	// HeapAlloc is bytes of allocated heap objects.
+	//
+	// "Allocated" heap objects include all reachable objects, as
+	// well as unreachable objects that the garbage collector has
+	// not yet freed. Specifically, HeapAlloc increases as heap
+	// objects are allocated and decreases as the heap is swept
+	// and unreachable objects are freed. Sweeping occurs
+	// incrementally between GC cycles, so these two processes
+	// occur simultaneously, and as a result HeapAlloc tends to
+	// change smoothly (in contrast with the sawtooth that is
+	// typical of stop-the-world garbage collectors).
+	HeapAlloc uint64
+
+	// HeapSys is bytes of heap memory obtained from the OS.
+	//
+	// HeapSys measures the amount of virtual address space
+	// reserved for the heap. This includes virtual address space
+	// that has been reserved but not yet used, which consumes no
+	// physical memory, but tends to be small, as well as virtual
+	// address space for which the physical memory has been
+	// returned to the OS after it became unused (see HeapReleased
+	// for a measure of the latter).
+	//
+	// HeapSys estimates the largest size the heap has had.
+	HeapSys uint64
+
+	// HeapIdle is bytes in idle (unused) spans.
+	//
+	// Idle spans have no objects in them. These spans could be
+	// (and may already have been) returned to the OS, or they can
+	// be reused for heap allocations, or they can be reused as
+	// stack memory.
+	//
+	// HeapIdle minus HeapReleased estimates the amount of memory
+	// that could be returned to the OS, but is being retained by
+	// the runtime so it can grow the heap without requesting more
+	// memory from the OS. If this difference is significantly
+	// larger than the heap size, it indicates there was a recent
+	// transient spike in live heap size.
+	HeapIdle uint64
+
+	// HeapInuse is bytes in in-use spans.
+	//
+	// In-use spans have at least one object in them. These spans
+	// can only be used for other objects of roughly the same
+	// size.
+	//
+	// HeapInuse minus HeapAlloc estimates the amount of memory
+	// that has been dedicated to particular size classes, but is
+	// not currently being used. This is an upper bound on
+	// fragmentation, but in general this memory can be reused
+	// efficiently.
+	HeapInuse uint64
+
+	// HeapReleased is bytes of physical memory returned to the OS.
+	//
+	// This counts heap memory from idle spans that was returned
+	// to the OS and has not yet been reacquired for the heap.
+	HeapReleased uint64
+
+	// HeapObjects is the number of allocated heap objects.
+	//
+	// Like HeapAlloc, this increases as objects are allocated and
+	// decreases as the heap is swept and unreachable objects are
+	// freed.
+	HeapObjects uint64
+
+	// Stack memory statistics.
+	//
+	// Stacks are not considered part of the heap, but the runtime
+	// can reuse a span of heap memory for stack memory, and
+	// vice-versa.
+
+	// StackInuse is bytes in stack spans.
+	//
+	// In-use stack spans have at least one stack in them. These
+	// spans can only be used for other stacks of the same size.
+	//
+	// There is no StackIdle because unused stack spans are
+	// returned to the heap (and hence counted toward HeapIdle).
+	StackInuse uint64
+
+	// StackSys is bytes of stack memory obtained from the OS.
+	//
+	// StackSys is StackInuse, plus any memory obtained directly
+	// from the OS for OS thread stacks (which should be minimal).
+	StackSys uint64
+
+	// Off-heap memory statistics.
+	//
+	// The following statistics measure runtime-internal
+	// structures that are not allocated from heap memory (usually
+	// because they are part of implementing the heap). Unlike
+	// heap or stack memory, any memory allocated to these
+	// structures is dedicated to these structures.
+	//
+	// These are primarily useful for debugging runtime memory
+	// overheads.
+
+	// MSpanInuse is bytes of allocated mspan structures.
+	MSpanInuse uint64
+
+	// MSpanSys is bytes of memory obtained from the OS for mspan
+	// structures.
+	MSpanSys uint64
+
+	// MCacheInuse is bytes of allocated mcache structures.
+	MCacheInuse uint64
+
+	// MCacheSys is bytes of memory obtained from the OS for
+	// mcache structures.
+	MCacheSys uint64
+
+	// BuckHashSys is bytes of memory in profiling bucket hash tables.
+	BuckHashSys uint64
+
+	// GCSys is bytes of memory in garbage collection metadata.
+	GCSys uint64
+
+	// OtherSys is bytes of memory in miscellaneous off-heap
+	// runtime allocations.
+	OtherSys uint64
+
+	// Garbage collector statistics.
+
+	// NextGC is the target heap size of the next GC cycle.
+	//
+	// The garbage collector's goal is to keep HeapAlloc ≤ NextGC.
+	// At the end of each GC cycle, the target for the next cycle
+	// is computed based on the amount of reachable data and the
+	// value of GOGC.
+	NextGC uint64
+
+	// LastGC is the time the last garbage collection finished, as
+	// nanoseconds since 1970 (the UNIX epoch).
+	LastGC uint64
+
+	// PauseTotalNs is the cumulative nanoseconds in GC
+	// stop-the-world pauses since the program started.
+	//
+	// During a stop-the-world pause, all goroutines are paused
+	// and only the garbage collector can run.
+	PauseTotalNs uint64
+
+	// PauseNs is a circular buffer of recent GC stop-the-world
+	// pause times in nanoseconds.
+	//
+	// The most recent pause is at PauseNs[(NumGC+255)%256]. In
+	// general, PauseNs[N%256] records the time paused in the most
+	// recent N%256th GC cycle. There may be multiple pauses per
+	// GC cycle; this is the sum of all pauses during a cycle.
+	PauseNs [256]uint64
+
+	// PauseEnd is a circular buffer of recent GC pause end times,
+	// as nanoseconds since 1970 (the UNIX epoch).
+	//
+	// This buffer is filled the same way as PauseNs. There may be
+	// multiple pauses per GC cycle; this records the end of the
+	// last pause in a cycle.
+	PauseEnd [256]uint64
+
+	// NumGC is the number of completed GC cycles.
+	NumGC uint32
+
+	// NumForcedGC is the number of GC cycles that were forced by
+	// the application calling the GC function.
+	NumForcedGC uint32
+
+	// GCCPUFraction is the fraction of this program's available
+	// CPU time used by the GC since the program started.
+	//
+	// GCCPUFraction is expressed as a number between 0 and 1,
+	// where 0 means GC has consumed none of this program's CPU. A
+	// program's available CPU time is defined as the integral of
+	// GOMAXPROCS since the program started. That is, if
+	// GOMAXPROCS is 2 and a program has been running for 10
+	// seconds, its "available CPU" is 20 seconds. GCCPUFraction
+	// does not include CPU time used for write barrier activity.
+	//
+	// This is the same as the fraction of CPU reported by
+	// GODEBUG=gctrace=1.
+	GCCPUFraction float64
+
+	// EnableGC indicates that GC is enabled. It is always true,
+	// even if GOGC=off.
+	EnableGC bool
+
+	// DebugGC is currently unused.
+	DebugGC bool
+
+	// BySize reports per-size class allocation statistics.
+	//
+	// BySize[N] gives statistics for allocations of size S where
+	// BySize[N-1].Size < S ≤ BySize[N].Size.
+	//
+	// This does not report allocations larger than BySize[60].Size.
+	BySize [61]struct {
+		// Size is the maximum byte size of an object in this
+		// size class.
+		Size uint32
+
+		// Mallocs is the cumulative count of heap objects
+		// allocated in this size class. The cumulative bytes
+		// of allocation is Size*Mallocs. The number of live
+		// objects in this size class is Mallocs - Frees.
+		Mallocs uint64
+
+		// Frees is the cumulative count of heap objects freed
+		// in this size class.
+		Frees uint64
+	}
+}
+
+func init() {
+	if offset := unsafe.Offsetof(memstats.heapStats); offset%8 != 0 {
+		println(offset)
+		throw("memstats.heapStats not aligned to 8 bytes")
+	}
+	if offset := unsafe.Offsetof(memstats.gcPauseDist); offset%8 != 0 {
+		println(offset)
+		throw("memstats.gcPauseDist not aligned to 8 bytes")
+	}
+	// Ensure the size of heapStatsDelta causes adjacent fields/slots (e.g.
+	// [3]heapStatsDelta) to be 8-byte aligned.
+	if size := unsafe.Sizeof(heapStatsDelta{}); size%8 != 0 {
+		println(size)
+		throw("heapStatsDelta not a multiple of 8 bytes in size")
+	}
+}
+
+// ReadMemStats populates m with memory allocator statistics.
+//
+// The returned memory allocator statistics are up to date as of the
+// call to ReadMemStats. This is in contrast with a heap profile,
+// which is a snapshot as of the most recently completed garbage
+// collection cycle.
+func ReadMemStats(m *MemStats) {
+	stopTheWorld("read mem stats")
+
+	systemstack(func() {
+		readmemstats_m(m)
+	})
+
+	startTheWorld()
+}
+
+func readmemstats_m(stats *MemStats) {
+	updatememstats()
+
+	stats.Alloc = memstats.alloc
+	stats.TotalAlloc = memstats.total_alloc
+	stats.Sys = memstats.sys
+	stats.Mallocs = memstats.nmalloc
+	stats.Frees = memstats.nfree
+	stats.HeapAlloc = memstats.alloc
+	stats.HeapSys = memstats.heap_sys.load()
+	// By definition, HeapIdle is memory that was mapped
+	// for the heap but is not currently used to hold heap
+	// objects. It also specifically is memory that can be
+	// used for other purposes, like stacks, but this memory
+	// is subtracted out of HeapSys before it makes that
+	// transition. Put another way:
+	//
+	// heap_sys = bytes allocated from the OS for the heap - bytes ultimately used for non-heap purposes
+	// heap_idle = bytes allocated from the OS for the heap - bytes ultimately used for any purpose
+	//
+	// or
+	//
+	// heap_sys = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse
+	// heap_idle = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse - heap_inuse
+	//
+	// => heap_idle = heap_sys - heap_inuse
+	stats.HeapIdle = memstats.heap_sys.load() - memstats.heap_inuse
+	stats.HeapInuse = memstats.heap_inuse
+	stats.HeapReleased = memstats.heap_released
+	stats.HeapObjects = memstats.heap_objects
+	stats.StackInuse = memstats.stacks_inuse
+	// memstats.stacks_sys is only memory mapped directly for OS stacks.
+	// Add in heap-allocated stack memory for user consumption.
+	stats.StackSys = memstats.stacks_inuse + memstats.stacks_sys.load()
+	stats.MSpanInuse = memstats.mspan_inuse
+	stats.MSpanSys = memstats.mspan_sys.load()
+	stats.MCacheInuse = memstats.mcache_inuse
+	stats.MCacheSys = memstats.mcache_sys.load()
+	stats.BuckHashSys = memstats.buckhash_sys.load()
+	// MemStats defines GCSys as an aggregate of all memory related
+	// to the memory management system, but we track this memory
+	// at a more granular level in the runtime.
+	stats.GCSys = memstats.gcMiscSys.load() + memstats.gcWorkBufInUse + memstats.gcProgPtrScalarBitsInUse
+	stats.OtherSys = memstats.other_sys.load()
+	stats.NextGC = gcController.heapGoal
+	stats.LastGC = memstats.last_gc_unix
+	stats.PauseTotalNs = memstats.pause_total_ns
+	stats.PauseNs = memstats.pause_ns
+	stats.PauseEnd = memstats.pause_end
+	stats.NumGC = memstats.numgc
+	stats.NumForcedGC = memstats.numforcedgc
+	stats.GCCPUFraction = memstats.gc_cpu_fraction
+	stats.EnableGC = true
+
+	// Handle BySize. Copy N values, where N is
+	// the minimum of the lengths of the two arrays.
+	// Unfortunately copy() won't work here because
+	// the arrays have different structs.
+	//
+	// TODO(mknyszek): Consider renaming the fields
+	// of by_size's elements to align so we can use
+	// the copy built-in.
+	bySizeLen := len(stats.BySize)
+	if l := len(memstats.by_size); l < bySizeLen {
+		bySizeLen = l
+	}
+	for i := 0; i < bySizeLen; i++ {
+		stats.BySize[i].Size = memstats.by_size[i].size
+		stats.BySize[i].Mallocs = memstats.by_size[i].nmalloc
+		stats.BySize[i].Frees = memstats.by_size[i].nfree
+	}
+}
+
+//go:linkname readGCStats runtime/debug.readGCStats
+func readGCStats(pauses *[]uint64) {
+	systemstack(func() {
+		readGCStats_m(pauses)
+	})
+}
+
+// readGCStats_m must be called on the system stack because it acquires the heap
+// lock. See mheap for details.
+//go:systemstack
+func readGCStats_m(pauses *[]uint64) {
+	p := *pauses
+	// Calling code in runtime/debug should make the slice large enough.
+	if cap(p) < len(memstats.pause_ns)+3 {
+		throw("short slice passed to readGCStats")
+	}
+
+	// Pass back: pauses, pause ends, last gc (absolute time), number of gc, total pause ns.
+	lock(&mheap_.lock)
+
+	n := memstats.numgc
+	if n > uint32(len(memstats.pause_ns)) {
+		n = uint32(len(memstats.pause_ns))
+	}
+
+	// The pause buffer is circular. The most recent pause is at
+	// pause_ns[(numgc-1)%len(pause_ns)], and then backward
+	// from there to go back farther in time. We deliver the times
+	// most recent first (in p[0]).
+	p = p[:cap(p)]
+	for i := uint32(0); i < n; i++ {
+		j := (memstats.numgc - 1 - i) % uint32(len(memstats.pause_ns))
+		p[i] = memstats.pause_ns[j]
+		p[n+i] = memstats.pause_end[j]
+	}
+
+	p[n+n] = memstats.last_gc_unix
+	p[n+n+1] = uint64(memstats.numgc)
+	p[n+n+2] = memstats.pause_total_ns
+	unlock(&mheap_.lock)
+	*pauses = p[:n+n+3]
+}
+
+// Updates the memstats structure.
+//
+// The world must be stopped.
+//
+//go:nowritebarrier
+func updatememstats() {
+	assertWorldStopped()
+
+	// Flush mcaches to mcentral before doing anything else.
+	//
+	// Flushing to the mcentral may in general cause stats to
+	// change as mcentral data structures are manipulated.
+	systemstack(flushallmcaches)
+
+	memstats.mcache_inuse = uint64(mheap_.cachealloc.inuse)
+	memstats.mspan_inuse = uint64(mheap_.spanalloc.inuse)
+	memstats.sys = memstats.heap_sys.load() + memstats.stacks_sys.load() + memstats.mspan_sys.load() +
+		memstats.mcache_sys.load() + memstats.buckhash_sys.load() + memstats.gcMiscSys.load() +
+		memstats.other_sys.load()
+
+	// Calculate memory allocator stats.
+	// During program execution we only count number of frees and amount of freed memory.
+	// Current number of alive objects in the heap and amount of alive heap memory
+	// are calculated by scanning all spans.
+	// Total number of mallocs is calculated as number of frees plus number of alive objects.
+	// Similarly, total amount of allocated memory is calculated as amount of freed memory
+	// plus amount of alive heap memory.
+	memstats.alloc = 0
+	memstats.total_alloc = 0
+	memstats.nmalloc = 0
+	memstats.nfree = 0
+	for i := 0; i < len(memstats.by_size); i++ {
+		memstats.by_size[i].nmalloc = 0
+		memstats.by_size[i].nfree = 0
+	}
+	// Collect consistent stats, which are the source-of-truth in the some cases.
+	var consStats heapStatsDelta
+	memstats.heapStats.unsafeRead(&consStats)
+
+	// Collect large allocation stats.
+	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 := consStats.smallAllocCount[i]
+		totalAlloc += a * uint64(class_to_size[i])
+		memstats.nmalloc += a
+		memstats.by_size[i].nmalloc = a
+
+		// Free stats.
+		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 += consStats.tinyAllocCount
+	memstats.nmalloc += consStats.tinyAllocCount
+
+	// Calculate derived stats.
+	memstats.total_alloc = totalAlloc
+	memstats.alloc = totalAlloc - totalFree
+	memstats.heap_objects = memstats.nmalloc - memstats.nfree
+
+	memstats.stacks_inuse = uint64(consStats.inStacks)
+	memstats.gcWorkBufInUse = uint64(consStats.inWorkBufs)
+	memstats.gcProgPtrScalarBitsInUse = uint64(consStats.inPtrScalarBits)
+
+	// We also count stacks_inuse, gcWorkBufInUse, and gcProgPtrScalarBitsInUse as sys memory.
+	memstats.sys += memstats.stacks_inuse + memstats.gcWorkBufInUse + memstats.gcProgPtrScalarBitsInUse
+
+	// 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
+	//
+	// Check if that's actually true.
+	//
+	// TODO(mknyszek): Maybe don't throw here. It would be bad if a
+	// bug in otherwise benign accounting caused the whole application
+	// to crash.
+	if memstats.heap_inuse != uint64(consStats.inHeap) {
+		print("runtime: heap_inuse=", memstats.heap_inuse, "\n")
+		print("runtime: consistent value=", consStats.inHeap, "\n")
+		throw("heap_inuse and consistent stats are not equal")
+	}
+	if memstats.heap_released != uint64(consStats.released) {
+		print("runtime: heap_released=", memstats.heap_released, "\n")
+		print("runtime: consistent value=", consStats.released, "\n")
+		throw("heap_released and consistent stats are not equal")
+	}
+	globalRetained := memstats.heap_sys.load() - memstats.heap_released
+	consRetained := uint64(consStats.committed - consStats.inStacks - consStats.inWorkBufs - consStats.inPtrScalarBits)
+	if globalRetained != consRetained {
+		print("runtime: global value=", globalRetained, "\n")
+		print("runtime: consistent value=", consRetained, "\n")
+		throw("measures of the retained heap are not equal")
+	}
+}
+
+// flushmcache flushes the mcache of allp[i].
+//
+// The world must be stopped.
+//
+//go:nowritebarrier
+func flushmcache(i int) {
+	assertWorldStopped()
+
+	p := allp[i]
+	c := p.mcache
+	if c == nil {
+		return
+	}
+	c.releaseAll()
+	stackcache_clear(c)
+}
+
+// flushallmcaches flushes the mcaches of all Ps.
+//
+// The world must be stopped.
+//
+//go:nowritebarrier
+func flushallmcaches() {
+	assertWorldStopped()
+
+	for i := 0; i < int(gomaxprocs); i++ {
+		flushmcache(i)
+	}
+}
+
+// sysMemStat represents a global system statistic that is managed atomically.
+//
+// This type must structurally be a uint64 so that mstats aligns with MemStats.
+type sysMemStat uint64
+
+// load atomically reads the value of the stat.
+//
+// Must be nosplit as it is called in runtime initialization, e.g. newosproc0.
+//go:nosplit
+func (s *sysMemStat) load() uint64 {
+	return atomic.Load64((*uint64)(s))
+}
+
+// add atomically adds the sysMemStat by n.
+//
+// Must be nosplit as it is called in runtime initialization, e.g. newosproc0.
+//go:nosplit
+func (s *sysMemStat) add(n int64) {
+	if s == nil {
+		return
+	}
+	val := atomic.Xadd64((*uint64)(s), n)
+	if (n > 0 && int64(val) < n) || (n < 0 && int64(val)+n < n) {
+		print("runtime: val=", val, " n=", n, "\n")
+		throw("sysMemStat overflow")
+	}
+}
+
+// heapStatsDelta contains deltas of various runtime memory statistics
+// that need to be updated together in order for them to be kept
+// consistent with one another.
+type heapStatsDelta struct {
+	// Memory stats.
+	committed       int64 // byte delta of memory committed
+	released        int64 // byte delta of released memory generated
+	inHeap          int64 // byte delta of memory placed in the heap
+	inStacks        int64 // byte delta of memory reserved for stacks
+	inWorkBufs      int64 // byte delta of memory reserved for work bufs
+	inPtrScalarBits int64 // byte delta of memory reserved for unrolled GC prog bits
+
+	// Allocator stats.
+	//
+	// 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)
+
+	// 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.
+func (a *heapStatsDelta) merge(b *heapStatsDelta) {
+	a.committed += b.committed
+	a.released += b.released
+	a.inHeap += b.inHeap
+	a.inStacks += b.inStacks
+	a.inWorkBufs += b.inWorkBufs
+	a.inPtrScalarBits += b.inPtrScalarBits
+
+	a.tinyAllocCount += b.tinyAllocCount
+	a.largeAlloc += b.largeAlloc
+	a.largeAllocCount += b.largeAllocCount
+	for i := range b.smallAllocCount {
+		a.smallAllocCount[i] += b.smallAllocCount[i]
+	}
+	a.largeFree += b.largeFree
+	a.largeFreeCount += b.largeFreeCount
+	for i := range b.smallFreeCount {
+		a.smallFreeCount[i] += b.smallFreeCount[i]
+	}
+}
+
+// consistentHeapStats represents a set of various memory statistics
+// whose updates must be viewed completely to get a consistent
+// state of the world.
+//
+// To write updates to memory stats use the acquire and release
+// methods. To obtain a consistent global snapshot of these statistics,
+// use read.
+type consistentHeapStats struct {
+	// stats is a ring buffer of heapStatsDelta values.
+	// Writers always atomically update the delta at index gen.
+	//
+	// Readers operate by rotating gen (0 -> 1 -> 2 -> 0 -> ...)
+	// and synchronizing with writers by observing each P's
+	// statsSeq field. If the reader observes a P not writing,
+	// it can be sure that it will pick up the new gen value the
+	// next time it writes.
+	//
+	// The reader then takes responsibility by clearing space
+	// in the ring buffer for the next reader to rotate gen to
+	// that space (i.e. it merges in values from index (gen-2) mod 3
+	// to index (gen-1) mod 3, then clears the former).
+	//
+	// Note that this means only one reader can be reading at a time.
+	// There is no way for readers to synchronize.
+	//
+	// This process is why we need a ring buffer of size 3 instead
+	// of 2: one is for the writers, one contains the most recent
+	// data, and the last one is clear so writers can begin writing
+	// to it the moment gen is updated.
+	stats [3]heapStatsDelta
+
+	// gen represents the current index into which writers
+	// are writing, and can take on the value of 0, 1, or 2.
+	// This value is updated atomically.
+	gen uint32
+
+	// noPLock is intended to provide mutual exclusion for updating
+	// stats when no P is available. It does not block other writers
+	// with a P, only other writers without a P and the reader. Because
+	// stats are usually updated when a P is available, contention on
+	// this lock should be minimal.
+	noPLock mutex
+}
+
+// acquire returns a heapStatsDelta to be updated. In effect,
+// it acquires the shard for writing. release must be called
+// as soon as the relevant deltas are updated.
+//
+// The returned heapStatsDelta must be updated atomically.
+//
+// The caller's P must not change between acquire and
+// release. This also means that the caller should not
+// acquire a P or release its P in between. A P also must
+// not acquire a given consistentHeapStats if it hasn't
+// yet released it.
+//
+// nosplit because a stack growth in this function could
+// lead to a stack allocation that could reenter the
+// function.
+//
+//go:nosplit
+func (m *consistentHeapStats) acquire() *heapStatsDelta {
+	if pp := getg().m.p.ptr(); pp != nil {
+		seq := atomic.Xadd(&pp.statsSeq, 1)
+		if seq%2 == 0 {
+			// Should have been incremented to odd.
+			print("runtime: seq=", seq, "\n")
+			throw("bad sequence number")
+		}
+	} else {
+		lock(&m.noPLock)
+	}
+	gen := atomic.Load(&m.gen) % 3
+	return &m.stats[gen]
+}
+
+// release indicates that the writer is done modifying
+// the delta. The value returned by the corresponding
+// acquire must no longer be accessed or modified after
+// release is called.
+//
+// The caller's P must not change between acquire and
+// release. This also means that the caller should not
+// acquire a P or release its P in between.
+//
+// nosplit because a stack growth in this function could
+// lead to a stack allocation that causes another acquire
+// before this operation has completed.
+//
+//go:nosplit
+func (m *consistentHeapStats) release() {
+	if pp := getg().m.p.ptr(); pp != nil {
+		seq := atomic.Xadd(&pp.statsSeq, 1)
+		if seq%2 != 0 {
+			// Should have been incremented to even.
+			print("runtime: seq=", seq, "\n")
+			throw("bad sequence number")
+		}
+	} else {
+		unlock(&m.noPLock)
+	}
+}
+
+// unsafeRead aggregates the delta for this shard into out.
+//
+// Unsafe because it does so without any synchronization. The
+// world must be stopped.
+func (m *consistentHeapStats) unsafeRead(out *heapStatsDelta) {
+	assertWorldStopped()
+
+	for i := range m.stats {
+		out.merge(&m.stats[i])
+	}
+}
+
+// unsafeClear clears the shard.
+//
+// Unsafe because the world must be stopped and values should
+// be donated elsewhere before clearing.
+func (m *consistentHeapStats) unsafeClear() {
+	assertWorldStopped()
+
+	for i := range m.stats {
+		m.stats[i] = heapStatsDelta{}
+	}
+}
+
+// read takes a globally consistent snapshot of m
+// and puts the aggregated value in out. Even though out is a
+// heapStatsDelta, the resulting values should be complete and
+// valid statistic values.
+//
+// Not safe to call concurrently. The world must be stopped
+// or metricsSema must be held.
+func (m *consistentHeapStats) read(out *heapStatsDelta) {
+	// Getting preempted after this point is not safe because
+	// we read allp. We need to make sure a STW can't happen
+	// so it doesn't change out from under us.
+	mp := acquirem()
+
+	// Get the current generation. We can be confident that this
+	// will not change since read is serialized and is the only
+	// one that modifies currGen.
+	currGen := atomic.Load(&m.gen)
+	prevGen := currGen - 1
+	if currGen == 0 {
+		prevGen = 2
+	}
+
+	// Prevent writers without a P from writing while we update gen.
+	lock(&m.noPLock)
+
+	// Rotate gen, effectively taking a snapshot of the state of
+	// these statistics at the point of the exchange by moving
+	// writers to the next set of deltas.
+	//
+	// This exchange is safe to do because we won't race
+	// with anyone else trying to update this value.
+	atomic.Xchg(&m.gen, (currGen+1)%3)
+
+	// Allow P-less writers to continue. They'll be writing to the
+	// next generation now.
+	unlock(&m.noPLock)
+
+	for _, p := range allp {
+		// Spin until there are no more writers.
+		for atomic.Load(&p.statsSeq)%2 != 0 {
+		}
+	}
+
+	// At this point we've observed that each sequence
+	// number is even, so any future writers will observe
+	// the new gen value. That means it's safe to read from
+	// the other deltas in the stats buffer.
+
+	// Perform our responsibilities and free up
+	// stats[prevGen] for the next time we want to take
+	// a snapshot.
+	m.stats[currGen].merge(&m.stats[prevGen])
+	m.stats[prevGen] = heapStatsDelta{}
+
+	// Finally, copy out the complete delta.
+	*out = m.stats[currGen]
+
+	releasem(mp)
+}