package runtime
import (
+ "internal/goexperiment"
"runtime/internal/atomic"
"unsafe"
)
// State of background sweep.
type sweepdata struct {
- lock mutex
- g *g
- parked bool
- started bool
-
- nbgsweep uint32
- npausesweep uint32
+ lock mutex
+ g *g
+ parked bool
// active tracks outstanding sweepers and the sweep
// termination condition.
return
}
if debug.gcpacertrace > 0 {
- print("pacer: sweep done at heap size ", gcController.heapLive>>20, "MB; allocated ", (gcController.heapLive-mheap_.sweepHeapLiveBasis)>>20, "MB during sweep; swept ", mheap_.pagesSwept.Load(), " pages at ", mheap_.sweepPagesPerByte, " pages/byte\n")
+ live := gcController.heapLive.Load()
+ print("pacer: sweep done at heap size ", live>>20, "MB; allocated ", (live-mheap_.sweepHeapLiveBasis)>>20, "MB during sweep; swept ", mheap_.pagesSwept.Load(), " pages at ", mheap_.sweepPagesPerByte, " pages/byte\n")
}
return
}
// instantly. If GC was forced before the concurrent sweep
// finished, there may be spans to sweep.
for sweepone() != ^uintptr(0) {
- sweep.npausesweep++
}
// Make sure there aren't any outstanding sweepers left.
c.fullUnswept(sg).reset()
}
- // Sweeping is done, so if the scavenger isn't already awake,
- // wake it up. There's definitely work for it to do at this
- // point.
- wakeScavenger()
+ // Sweeping is done, so there won't be any new memory to
+ // scavenge for a bit.
+ //
+ // If the scavenger isn't already awake, wake it up. There's
+ // definitely work for it to do at this point.
+ scavenger.wake()
nextMarkBitArenaEpoch()
}
lock(&sweep.lock)
sweep.parked = true
c <- 1
- goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceEvGoBlock, 1)
+ goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceBlockGCSweep, 1)
for {
+ // bgsweep attempts to be a "low priority" goroutine by intentionally
+ // yielding time. It's OK if it doesn't run, because goroutines allocating
+ // memory will sweep and ensure that all spans are swept before the next
+ // GC cycle. We really only want to run when we're idle.
+ //
+ // However, calling Gosched after each span swept produces a tremendous
+ // amount of tracing events, sometimes up to 50% of events in a trace. It's
+ // also inefficient to call into the scheduler so much because sweeping a
+ // single span is in general a very fast operation, taking as little as 30 ns
+ // on modern hardware. (See #54767.)
+ //
+ // As a result, bgsweep sweeps in batches, and only calls into the scheduler
+ // at the end of every batch. Furthermore, it only yields its time if there
+ // isn't spare idle time available on other cores. If there's available idle
+ // time, helping to sweep can reduce allocation latencies by getting ahead of
+ // the proportional sweeper and having spans ready to go for allocation.
+ const sweepBatchSize = 10
+ nSwept := 0
for sweepone() != ^uintptr(0) {
- sweep.nbgsweep++
- Gosched()
+ nSwept++
+ if nSwept%sweepBatchSize == 0 {
+ goschedIfBusy()
+ }
}
for freeSomeWbufs(true) {
- Gosched()
+ // N.B. freeSomeWbufs is already batched internally.
+ goschedIfBusy()
}
lock(&sweep.lock)
if !isSweepDone() {
continue
}
sweep.parked = true
- goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceEvGoBlock, 1)
+ goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceBlockGCSweep, 1)
}
}
// between sweep done and sweep termination (e.g. not enough
// allocations to trigger a GC) which would be nice to fill in
// with scavenging work.
- systemstack(func() {
- lock(&mheap_.lock)
- mheap_.pages.scavengeStartGen()
- unlock(&mheap_.lock)
- })
- // Since we might sweep in an allocation path, it's not possible
- // for us to wake the scavenger directly via wakeScavenger, since
- // it could allocate. Ask sysmon to do it for us instead.
- readyForScavenger()
+ if debug.scavtrace > 0 {
+ systemstack(func() {
+ lock(&mheap_.lock)
+
+ // Get released stats.
+ releasedBg := mheap_.pages.scav.releasedBg.Load()
+ releasedEager := mheap_.pages.scav.releasedEager.Load()
+
+ // Print the line.
+ printScavTrace(releasedBg, releasedEager, false)
+
+ // Update the stats.
+ mheap_.pages.scav.releasedBg.Add(-releasedBg)
+ mheap_.pages.scav.releasedEager.Add(-releasedEager)
+ unlock(&mheap_.lock)
+ })
+ }
+ scavenger.ready()
}
gp.m.locks--
// Caller must disable preemption.
// Otherwise when this function returns the span can become unswept again
// (if GC is triggered on another goroutine).
- _g_ := getg()
- if _g_.m.locks == 0 && _g_.m.mallocing == 0 && _g_ != _g_.m.g0 {
+ gp := getg()
+ if gp.m.locks == 0 && gp.m.mallocing == 0 && gp != gp.m.g0 {
throw("mspan.ensureSwept: m is not locked")
}
}
}
-// Sweep frees or collects finalizers for blocks not marked in the mark phase.
+// sweep frees or collects finalizers for blocks not marked in the mark phase.
// It clears the mark bits in preparation for the next GC round.
// Returns true if the span was returned to heap.
// If preserve=true, don't return it to heap nor relink in mcentral lists;
func (sl *sweepLocked) sweep(preserve bool) bool {
// It's critical that we enter this function with preemption disabled,
// GC must not start while we are in the middle of this function.
- _g_ := getg()
- if _g_.m.locks == 0 && _g_.m.mallocing == 0 && _g_ != _g_.m.g0 {
+ gp := getg()
+ if gp.m.locks == 0 && gp.m.mallocing == 0 && gp != gp.m.g0 {
throw("mspan.sweep: m is not locked")
}
throw("mspan.sweep: bad span state")
}
- if trace.enabled {
- traceGCSweepSpan(s.npages * _PageSize)
+ trace := traceAcquire()
+ if trace.ok() {
+ trace.GCSweepSpan(s.npages * _PageSize)
+ traceRelease(trace)
}
mheap_.pagesSwept.Add(int64(s.npages))
// efficient; allocfreetrace has massive overhead.
mbits := s.markBitsForBase()
abits := s.allocBitsForIndex(0)
- for i := uintptr(0); i < s.nelems; i++ {
- if !mbits.isMarked() && (abits.index < s.freeindex || abits.isMarked()) {
+ for i := uintptr(0); i < uintptr(s.nelems); i++ {
+ if !mbits.isMarked() && (abits.index < uintptr(s.freeindex) || abits.isMarked()) {
x := s.base() + i*s.elemsize
if debug.allocfreetrace != 0 {
tracefree(unsafe.Pointer(x), size)
if debug.clobberfree != 0 {
clobberfree(unsafe.Pointer(x), size)
}
- if raceenabled {
+ // User arenas are handled on explicit free.
+ if raceenabled && !s.isUserArenaChunk {
racefree(unsafe.Pointer(x), size)
}
- if msanenabled {
+ if msanenabled && !s.isUserArenaChunk {
msanfree(unsafe.Pointer(x), size)
}
- if asanenabled {
+ if asanenabled && !s.isUserArenaChunk {
asanpoison(unsafe.Pointer(x), size)
}
}
//
// Check the first bitmap byte, where we have to be
// careful with freeindex.
- obj := s.freeindex
+ obj := uintptr(s.freeindex)
if (*s.gcmarkBits.bytep(obj / 8)&^*s.allocBits.bytep(obj / 8))>>(obj%8) != 0 {
s.reportZombies()
}
// Check remaining bytes.
- for i := obj/8 + 1; i < divRoundUp(s.nelems, 8); i++ {
+ for i := obj/8 + 1; i < divRoundUp(uintptr(s.nelems), 8); i++ {
if *s.gcmarkBits.bytep(i)&^*s.allocBits.bytep(i) != 0 {
s.reportZombies()
}
s.allocCount = nalloc
s.freeindex = 0 // reset allocation index to start of span.
- if trace.enabled {
- getg().m.p.ptr().traceReclaimed += uintptr(nfreed) * s.elemsize
+ s.freeIndexForScan = 0
+ if traceEnabled() {
+ getg().m.p.ptr().trace.reclaimed += uintptr(nfreed) * s.elemsize
}
// gcmarkBits becomes the allocBits.
// get a fresh cleared gcmarkBits in preparation for next GC
s.allocBits = s.gcmarkBits
- s.gcmarkBits = newMarkBits(s.nelems)
+ s.gcmarkBits = newMarkBits(uintptr(s.nelems))
+
+ // refresh pinnerBits if they exists
+ if s.pinnerBits != nil {
+ s.refreshPinnerBits()
+ }
// Initialize alloc bits cache.
s.refillAllocCache(0)
// to go so release the span.
atomic.Store(&s.sweepgen, sweepgen)
+ if s.isUserArenaChunk {
+ if preserve {
+ // This is a case that should never be handled by a sweeper that
+ // preserves the span for reuse.
+ throw("sweep: tried to preserve a user arena span")
+ }
+ if nalloc > 0 {
+ // There still exist pointers into the span or the span hasn't been
+ // freed yet. It's not ready to be reused. Put it back on the
+ // full swept list for the next cycle.
+ mheap_.central[spc].mcentral.fullSwept(sweepgen).push(s)
+ return false
+ }
+
+ // It's only at this point that the sweeper doesn't actually need to look
+ // at this arena anymore, so subtract from pagesInUse now.
+ mheap_.pagesInUse.Add(-s.npages)
+ s.state.set(mSpanDead)
+
+ // The arena is ready to be recycled. Remove it from the quarantine list
+ // and place it on the ready list. Don't add it back to any sweep lists.
+ systemstack(func() {
+ // It's the arena code's responsibility to get the chunk on the quarantine
+ // list by the time all references to the chunk are gone.
+ if s.list != &mheap_.userArena.quarantineList {
+ throw("user arena span is on the wrong list")
+ }
+ lock(&mheap_.lock)
+ mheap_.userArena.quarantineList.remove(s)
+ mheap_.userArena.readyList.insert(s)
+ unlock(&mheap_.lock)
+ })
+ return false
+ }
+
if spc.sizeclass() != 0 {
// Handle spans for small objects.
if nfreed > 0 {
// 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()
+
+ // Count the frees in the inconsistent, internal stats.
+ gcController.totalFree.Add(int64(nfreed) * int64(s.elemsize))
}
if !preserve {
// The caller may not have removed this span from whatever
return true
}
// Return span back to the right mcentral list.
- if uintptr(nalloc) == s.nelems {
+ if nalloc == s.nelems {
mheap_.central[spc].mcentral.fullSwept(sweepgen).push(s)
} else {
mheap_.central[spc].mcentral.partialSwept(sweepgen).push(s)
} else {
mheap_.freeSpan(s)
}
+ if goexperiment.AllocHeaders && s.largeType != nil && s.largeType.Kind_&kindGCProg != 0 {
+ // In the allocheaders experiment, the unrolled GCProg bitmap is allocated separately.
+ // Free the space for the unrolled bitmap.
+ systemstack(func() {
+ s := spanOf(uintptr(unsafe.Pointer(s.largeType)))
+ mheap_.freeManual(s, spanAllocPtrScalarBits)
+ })
+ s.largeType = nil
+ }
+
+ // Count the free in the consistent, external stats.
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()
+
+ // Count the free in the inconsistent, internal stats.
+ gcController.totalFree.Add(int64(size))
+
return true
}
print("runtime: marked free object in span ", s, ", elemsize=", s.elemsize, " freeindex=", s.freeindex, " (bad use of unsafe.Pointer? try -d=checkptr)\n")
mbits := s.markBitsForBase()
abits := s.allocBitsForIndex(0)
- for i := uintptr(0); i < s.nelems; i++ {
+ for i := uintptr(0); i < uintptr(s.nelems); i++ {
addr := s.base() + i*s.elemsize
print(hex(addr))
- alloc := i < s.freeindex || abits.isMarked()
+ alloc := i < uintptr(s.freeindex) || abits.isMarked()
if alloc {
print(" alloc")
} else {
return
}
- if trace.enabled {
- traceGCSweepStart()
+ trace := traceAcquire()
+ if trace.ok() {
+ trace.GCSweepStart()
+ traceRelease(trace)
}
+ // Fix debt if necessary.
retry:
sweptBasis := mheap_.pagesSweptBasis.Load()
-
- // Fix debt if necessary.
- newHeapLive := uintptr(atomic.Load64(&gcController.heapLive)-mheap_.sweepHeapLiveBasis) + spanBytes
+ live := gcController.heapLive.Load()
+ liveBasis := mheap_.sweepHeapLiveBasis
+ newHeapLive := spanBytes
+ if liveBasis < live {
+ // Only do this subtraction when we don't overflow. Otherwise, pagesTarget
+ // might be computed as something really huge, causing us to get stuck
+ // sweeping here until the next mark phase.
+ //
+ // Overflow can happen here if gcPaceSweeper is called concurrently with
+ // sweeping (i.e. not during a STW, like it usually is) because this code
+ // is intentionally racy. A concurrent call to gcPaceSweeper can happen
+ // if a GC tuning parameter is modified and we read an older value of
+ // heapLive than what was used to set the basis.
+ //
+ // This state should be transient, so it's fine to just let newHeapLive
+ // be a relatively small number. We'll probably just skip this attempt to
+ // sweep.
+ //
+ // See issue #57523.
+ newHeapLive += uintptr(live - liveBasis)
+ }
pagesTarget := int64(mheap_.sweepPagesPerByte*float64(newHeapLive)) - int64(callerSweepPages)
for pagesTarget > int64(mheap_.pagesSwept.Load()-sweptBasis) {
if sweepone() == ^uintptr(0) {
}
}
- if trace.enabled {
- traceGCSweepDone()
+ trace = traceAcquire()
+ if trace.ok() {
+ trace.GCSweepDone()
+ traceRelease(trace)
}
}
// trigger. Compute the ratio of in-use pages to sweep
// per byte allocated, accounting for the fact that
// some might already be swept.
- heapLiveBasis := atomic.Load64(&gcController.heapLive)
+ heapLiveBasis := gcController.heapLive.Load()
heapDistance := int64(trigger) - int64(heapLiveBasis)
// Add a little margin so rounding errors and
// concurrent sweep are less likely to leave pages