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// 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 (
type mstats struct {
// Statistics about malloc heap.
heapStats consistentHeapStats
// Statistics about stacks.
stacks_sys sysMemStat // only counts newosproc0 stack in mstats; differs from MemStats.StackSys
// Statistics about allocation of low-level fixed-size structures.
mspan_sys sysMemStat
mcache_sys sysMemStat
buckhash_sys sysMemStat // profiling bucket hash table
// Statistics about GC overhead.
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 worldsema 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
last_gc_nanotime uint64 // last gc (monotonic time)
lastHeapInUse uint64 // heapInUse at mark termination of the previous GC
enablegc bool
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.
// In non-cgo programs this metric is currently equal to StackInuse
// (but this should not be relied upon, and the value may change in
// the future).
// In cgo programs this metric includes OS thread stacks allocated
// directly from the OS. Currently, this only accounts for one stack in
// c-shared and c-archive build modes and other sources of stacks from
// the OS (notably, any allocated by C code) are not currently measured.
// Note this too may change in the future.
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 {
throw("memstats.heapStats 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 {
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) {
_ = m.Alloc // nil check test before we switch stacks, see issue 61158
stw := stopTheWorld(stwReadMemStats)
systemstack(func() {
// doubleCheckReadMemStats controls a double-check mode for ReadMemStats that
// ensures consistency between the values that ReadMemStats is using and the
// runtime-internal stats.
var doubleCheckReadMemStats = false
// readmemstats_m populates stats for internal runtime values.
// The world must be stopped.
func readmemstats_m(stats *MemStats) {
// 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.
// 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.
// Collect consistent stats, which are the source-of-truth in some cases.
var consStats heapStatsDelta
// Collect large allocation stats.
totalAlloc := consStats.largeAlloc
nMalloc := consStats.largeAllocCount
totalFree := consStats.largeFree
nFree := consStats.largeFreeCount
// Collect per-sizeclass stats.
var bySize [_NumSizeClasses]struct {
Size uint32
Mallocs uint64
Frees uint64
for i := range bySize {
bySize[i].Size = uint32(class_to_size[i])
// Malloc stats.
a := consStats.smallAllocCount[i]
totalAlloc += a * uint64(class_to_size[i])
nMalloc += a
bySize[i].Mallocs = a
// Free stats.
f := consStats.smallFreeCount[i]
totalFree += f * uint64(class_to_size[i])
nFree += f
bySize[i].Frees = f
// Account for tiny allocations.
// For historical reasons, MemStats includes tiny allocations
// in both the total free and total alloc count. This double-counts
// memory in some sense because their tiny allocation block is also
// counted. Tracking the lifetime of individual tiny allocations is
// currently not done because it would be too expensive.
nFree += consStats.tinyAllocCount
nMalloc += consStats.tinyAllocCount
// Calculate derived stats.
stackInUse := uint64(consStats.inStacks)
gcWorkBufInUse := uint64(consStats.inWorkBufs)
gcProgPtrScalarBitsInUse := uint64(consStats.inPtrScalarBits)
totalMapped := gcController.heapInUse.load() + gcController.heapFree.load() + gcController.heapReleased.load() +
memstats.stacks_sys.load() + memstats.mspan_sys.load() + memstats.mcache_sys.load() +
memstats.buckhash_sys.load() + memstats.gcMiscSys.load() + memstats.other_sys.load() +
stackInUse + gcWorkBufInUse + gcProgPtrScalarBitsInUse
heapGoal := gcController.heapGoal()
if doubleCheckReadMemStats {
// Only check this if we're debugging. It would be bad to crash an application
// just because the debugging stats are wrong. We mostly rely on tests to catch
// these issues, and we enable the double check mode for tests.
// The world is stopped, so the consistent stats (after aggregation)
// should be identical to some combination of memstats. In particular:
// * memstats.heapInUse == inHeap
// * memstats.heapReleased == released
// * memstats.heapInUse + memstats.heapFree == committed - inStacks - inWorkBufs - inPtrScalarBits
// * memstats.totalAlloc == totalAlloc
// * memstats.totalFree == totalFree
// Check if that's actually true.
// Prevent sysmon and the tracer from skewing the stats since they can
// act without synchronizing with a STW. See #64401.
if gcController.heapInUse.load() != uint64(consStats.inHeap) {
print("runtime: heapInUse=", gcController.heapInUse.load(), "\n")
print("runtime: consistent value=", consStats.inHeap, "\n")
throw("heapInUse and consistent stats are not equal")
if gcController.heapReleased.load() != uint64(consStats.released) {
print("runtime: heapReleased=", gcController.heapReleased.load(), "\n")
print("runtime: consistent value=", consStats.released, "\n")
throw("heapReleased and consistent stats are not equal")
heapRetained := gcController.heapInUse.load() + gcController.heapFree.load()
consRetained := uint64(consStats.committed - consStats.inStacks - consStats.inWorkBufs - consStats.inPtrScalarBits)
if heapRetained != consRetained {
print("runtime: global value=", heapRetained, "\n")
print("runtime: consistent value=", consRetained, "\n")
throw("measures of the retained heap are not equal")
if gcController.totalAlloc.Load() != totalAlloc {
print("runtime: totalAlloc=", gcController.totalAlloc.Load(), "\n")
print("runtime: consistent value=", totalAlloc, "\n")
throw("totalAlloc and consistent stats are not equal")
if gcController.totalFree.Load() != totalFree {
print("runtime: totalFree=", gcController.totalFree.Load(), "\n")
print("runtime: consistent value=", totalFree, "\n")
throw("totalFree and consistent stats are not equal")
// Also check that mappedReady lines up with totalMapped - released.
// This isn't really the same type of "make sure consistent stats line up" situation,
// but this is an opportune time to check.
if gcController.mappedReady.Load() != totalMapped-uint64(consStats.released) {
print("runtime: mappedReady=", gcController.mappedReady.Load(), "\n")
print("runtime: totalMapped=", totalMapped, "\n")
print("runtime: released=", uint64(consStats.released), "\n")
print("runtime: totalMapped-released=", totalMapped-uint64(consStats.released), "\n")
throw("mappedReady and other memstats are not equal")
// We've calculated all the values we need. Now, populate stats.
stats.Alloc = totalAlloc - totalFree
stats.TotalAlloc = totalAlloc
stats.Sys = totalMapped
stats.Mallocs = nMalloc
stats.Frees = nFree
stats.HeapAlloc = totalAlloc - totalFree
stats.HeapSys = gcController.heapInUse.load() + gcController.heapFree.load() + gcController.heapReleased.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:
// HeapSys = bytes allocated from the OS for the heap - bytes ultimately used for non-heap purposes
// HeapIdle = bytes allocated from the OS for the heap - bytes ultimately used for any purpose
// or
// HeapSys = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse
// HeapIdle = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse - heapInUse
// => HeapIdle = HeapSys - heapInUse = heapFree + heapReleased
stats.HeapIdle = gcController.heapFree.load() + gcController.heapReleased.load()
stats.HeapInuse = gcController.heapInUse.load()
stats.HeapReleased = gcController.heapReleased.load()
stats.HeapObjects = nMalloc - nFree
stats.StackInuse = stackInUse
// memstats.stacks_sys is only memory mapped directly for OS stacks.
// Add in heap-allocated stack memory for user consumption.
stats.StackSys = stackInUse + memstats.stacks_sys.load()
stats.MSpanInuse = uint64(mheap_.spanalloc.inuse)
stats.MSpanSys = memstats.mspan_sys.load()
stats.MCacheInuse = uint64(mheap_.cachealloc.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() + gcWorkBufInUse + gcProgPtrScalarBitsInUse
stats.OtherSys = memstats.other_sys.load()
stats.NextGC = 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
// stats.BySize and bySize might not match in length.
// That's OK, stats.BySize cannot change due to backwards
// compatibility issues. copy will copy the minimum amount
// of values between the two of them.
copy(stats.BySize[:], bySize[:])
//go:linkname readGCStats runtime/debug.readGCStats
func readGCStats(pauses *[]uint64) {
systemstack(func() {
// readGCStats_m must be called on the system stack because it acquires the heap
// lock. See mheap for details.
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.
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
*pauses = p[:n+n+3]
// flushmcache flushes the mcache of allp[i].
// The world must be stopped.
func flushmcache(i int) {
p := allp[i]
c := p.mcache
if c == nil {
// flushallmcaches flushes the mcaches of all Ps.
// The world must be stopped.
func flushallmcaches() {
for i := 0; i < int(gomaxprocs); 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.
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.
func (s *sysMemStat) add(n int64) {
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.
gen atomic.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.
func (m *consistentHeapStats) acquire() *heapStatsDelta {
if pp := getg().m.p.ptr(); pp != nil {
seq := pp.statsSeq.Add(1)
if seq%2 == 0 {
// Should have been incremented to odd.
print("runtime: seq=", seq, "\n")
throw("bad sequence number")
} else {
gen := m.gen.Load() % 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.
func (m *consistentHeapStats) release() {
if pp := getg().m.p.ptr(); pp != nil {
seq := pp.statsSeq.Add(1)
if seq%2 != 0 {
// Should have been incremented to even.
print("runtime: seq=", seq, "\n")
throw("bad sequence number")
} else {
// 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) {
for i := range m.stats {
// unsafeClear clears the shard.
// Unsafe because the world must be stopped and values should
// be donated elsewhere before clearing.
func (m *consistentHeapStats) unsafeClear() {
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 := m.gen.Load()
prevGen := currGen - 1
if currGen == 0 {
prevGen = 2
// Prevent writers without a P from writing while we update gen.
// 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.
m.gen.Swap((currGen + 1) % 3)
// Allow P-less writers to continue. They'll be writing to the
// next generation now.
for _, p := range allp {
// Spin until there are no more writers.
for p.statsSeq.Load()%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[prevGen] = heapStatsDelta{}
// Finally, copy out the complete delta.
*out = m.stats[currGen]
type cpuStats struct {
// All fields are CPU time in nanoseconds computed by comparing
// calls of nanotime. This means they're all overestimates, because
// they don't accurately compute on-CPU time (so some of the time
// could be spent scheduled away by the OS).
GCAssistTime int64 // GC assists
GCDedicatedTime int64 // GC dedicated mark workers + pauses
GCIdleTime int64 // GC idle mark workers
GCPauseTime int64 // GC pauses (all GOMAXPROCS, even if just 1 is running)
GCTotalTime int64
ScavengeAssistTime int64 // background scavenger
ScavengeBgTime int64 // scavenge assists
ScavengeTotalTime int64
IdleTime int64 // Time Ps spent in _Pidle.
UserTime int64 // Time Ps spent in _Prunning or _Psyscall that's not any of the above.
TotalTime int64 // GOMAXPROCS * (monotonic wall clock time elapsed)
// accumulateGCPauseTime add dt*stwProcs to the GC CPU pause time stats. dt should be
// the actual time spent paused, for orthogonality. maxProcs should be GOMAXPROCS,
// not work.stwprocs, since this number must be comparable to a total time computed
func (s *cpuStats) accumulateGCPauseTime(dt int64, maxProcs int32) {
cpu := dt * int64(maxProcs)
s.GCPauseTime += cpu
s.GCTotalTime += cpu
// accumulate takes a cpuStats and adds in the current state of all GC CPU
// counters.
// gcMarkPhase indicates that we're in the mark phase and that certain counter
// values should be used.
func (s *cpuStats) accumulate(now int64, gcMarkPhase bool) {
// N.B. Mark termination and sweep termination pauses are
// accumulated in work.cpuStats at the end of their respective pauses.
var (
markAssistCpu int64
markDedicatedCpu int64
markFractionalCpu int64
markIdleCpu int64
if gcMarkPhase {
// N.B. These stats may have stale values if the GC is not
// currently in the mark phase.
markAssistCpu = gcController.assistTime.Load()
markDedicatedCpu = gcController.dedicatedMarkTime.Load()
markFractionalCpu = gcController.fractionalMarkTime.Load()
markIdleCpu = gcController.idleMarkTime.Load()
// The rest of the stats below are either derived from the above or
// are reset on each mark termination.
scavAssistCpu := scavenge.assistTime.Load()
scavBgCpu := scavenge.backgroundTime.Load()
// Update cumulative GC CPU stats.
s.GCAssistTime += markAssistCpu
s.GCDedicatedTime += markDedicatedCpu + markFractionalCpu
s.GCIdleTime += markIdleCpu
s.GCTotalTime += markAssistCpu + markDedicatedCpu + markFractionalCpu + markIdleCpu
// Update cumulative scavenge CPU stats.
s.ScavengeAssistTime += scavAssistCpu
s.ScavengeBgTime += scavBgCpu
s.ScavengeTotalTime += scavAssistCpu + scavBgCpu
// Update total CPU.
s.TotalTime = sched.totaltime + (now-sched.procresizetime)*int64(gomaxprocs)
s.IdleTime += sched.idleTime.Load()
// Compute userTime. We compute this indirectly as everything that's not the above.
// Since time spent in _Pgcstop is covered by gcPauseTime, and time spent in _Pidle
// is covered by idleTime, what we're left with is time spent in _Prunning and _Psyscall,
// the latter of which is fine because the P will either go idle or get used for something
// else via sysmon. Meanwhile if we subtract GC time from whatever's left, we get non-GC
// _Prunning time. Note that this still leaves time spent in sweeping and in the scheduler,
// but that's fine. The overwhelming majority of this time will be actual user time.
s.UserTime = s.TotalTime - (s.GCTotalTime + s.ScavengeTotalTime + s.IdleTime)