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Diffstat (limited to 'src/runtime/mgcmark.go')
| -rw-r--r-- | src/runtime/mgcmark.go | 1591 |
1 files changed, 1591 insertions, 0 deletions
diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go new file mode 100644 index 0000000..0bf044e --- /dev/null +++ b/src/runtime/mgcmark.go @@ -0,0 +1,1591 @@ +// 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. + +// Garbage collector: marking and scanning + +package runtime + +import ( + "internal/goarch" + "internal/goexperiment" + "runtime/internal/atomic" + "runtime/internal/sys" + "unsafe" +) + +const ( + fixedRootFinalizers = iota + fixedRootFreeGStacks + fixedRootCount + + // rootBlockBytes is the number of bytes to scan per data or + // BSS root. + rootBlockBytes = 256 << 10 + + // maxObletBytes is the maximum bytes of an object to scan at + // once. Larger objects will be split up into "oblets" of at + // most this size. Since we can scan 1–2 MB/ms, 128 KB bounds + // scan preemption at ~100 µs. + // + // This must be > _MaxSmallSize so that the object base is the + // span base. + maxObletBytes = 128 << 10 + + // drainCheckThreshold specifies how many units of work to do + // between self-preemption checks in gcDrain. Assuming a scan + // rate of 1 MB/ms, this is ~100 µs. Lower values have higher + // overhead in the scan loop (the scheduler check may perform + // a syscall, so its overhead is nontrivial). Higher values + // make the system less responsive to incoming work. + drainCheckThreshold = 100000 + + // pagesPerSpanRoot indicates how many pages to scan from a span root + // at a time. Used by special root marking. + // + // Higher values improve throughput by increasing locality, but + // increase the minimum latency of a marking operation. + // + // Must be a multiple of the pageInUse bitmap element size and + // must also evenly divide pagesPerArena. + pagesPerSpanRoot = 512 +) + +// gcMarkRootPrepare queues root scanning jobs (stacks, globals, and +// some miscellany) and initializes scanning-related state. +// +// The world must be stopped. +func gcMarkRootPrepare() { + assertWorldStopped() + + // Compute how many data and BSS root blocks there are. + nBlocks := func(bytes uintptr) int { + return int(divRoundUp(bytes, rootBlockBytes)) + } + + work.nDataRoots = 0 + work.nBSSRoots = 0 + + // Scan globals. + for _, datap := range activeModules() { + nDataRoots := nBlocks(datap.edata - datap.data) + if nDataRoots > work.nDataRoots { + work.nDataRoots = nDataRoots + } + } + + for _, datap := range activeModules() { + nBSSRoots := nBlocks(datap.ebss - datap.bss) + if nBSSRoots > work.nBSSRoots { + work.nBSSRoots = nBSSRoots + } + } + + // Scan span roots for finalizer specials. + // + // We depend on addfinalizer to mark objects that get + // finalizers after root marking. + // + // We're going to scan the whole heap (that was available at the time the + // mark phase started, i.e. markArenas) for in-use spans which have specials. + // + // Break up the work into arenas, and further into chunks. + // + // Snapshot allArenas as markArenas. This snapshot is safe because allArenas + // is append-only. + mheap_.markArenas = mheap_.allArenas[:len(mheap_.allArenas):len(mheap_.allArenas)] + work.nSpanRoots = len(mheap_.markArenas) * (pagesPerArena / pagesPerSpanRoot) + + // Scan stacks. + // + // Gs may be created after this point, but it's okay that we + // ignore them because they begin life without any roots, so + // there's nothing to scan, and any roots they create during + // the concurrent phase will be caught by the write barrier. + work.stackRoots = allGsSnapshot() + work.nStackRoots = len(work.stackRoots) + + work.markrootNext = 0 + work.markrootJobs = uint32(fixedRootCount + work.nDataRoots + work.nBSSRoots + work.nSpanRoots + work.nStackRoots) + + // Calculate base indexes of each root type + work.baseData = uint32(fixedRootCount) + work.baseBSS = work.baseData + uint32(work.nDataRoots) + work.baseSpans = work.baseBSS + uint32(work.nBSSRoots) + work.baseStacks = work.baseSpans + uint32(work.nSpanRoots) + work.baseEnd = work.baseStacks + uint32(work.nStackRoots) +} + +// gcMarkRootCheck checks that all roots have been scanned. It is +// purely for debugging. +func gcMarkRootCheck() { + if work.markrootNext < work.markrootJobs { + print(work.markrootNext, " of ", work.markrootJobs, " markroot jobs done\n") + throw("left over markroot jobs") + } + + // Check that stacks have been scanned. + // + // We only check the first nStackRoots Gs that we should have scanned. + // Since we don't care about newer Gs (see comment in + // gcMarkRootPrepare), no locking is required. + i := 0 + forEachGRace(func(gp *g) { + if i >= work.nStackRoots { + return + } + + if !gp.gcscandone { + println("gp", gp, "goid", gp.goid, + "status", readgstatus(gp), + "gcscandone", gp.gcscandone) + throw("scan missed a g") + } + + i++ + }) +} + +// ptrmask for an allocation containing a single pointer. +var oneptrmask = [...]uint8{1} + +// markroot scans the i'th root. +// +// Preemption must be disabled (because this uses a gcWork). +// +// Returns the amount of GC work credit produced by the operation. +// If flushBgCredit is true, then that credit is also flushed +// to the background credit pool. +// +// nowritebarrier is only advisory here. +// +//go:nowritebarrier +func markroot(gcw *gcWork, i uint32, flushBgCredit bool) int64 { + // Note: if you add a case here, please also update heapdump.go:dumproots. + var workDone int64 + var workCounter *atomic.Int64 + switch { + case work.baseData <= i && i < work.baseBSS: + workCounter = &gcController.globalsScanWork + for _, datap := range activeModules() { + workDone += markrootBlock(datap.data, datap.edata-datap.data, datap.gcdatamask.bytedata, gcw, int(i-work.baseData)) + } + + case work.baseBSS <= i && i < work.baseSpans: + workCounter = &gcController.globalsScanWork + for _, datap := range activeModules() { + workDone += markrootBlock(datap.bss, datap.ebss-datap.bss, datap.gcbssmask.bytedata, gcw, int(i-work.baseBSS)) + } + + case i == fixedRootFinalizers: + for fb := allfin; fb != nil; fb = fb.alllink { + cnt := uintptr(atomic.Load(&fb.cnt)) + scanblock(uintptr(unsafe.Pointer(&fb.fin[0])), cnt*unsafe.Sizeof(fb.fin[0]), &finptrmask[0], gcw, nil) + } + + case i == fixedRootFreeGStacks: + // Switch to the system stack so we can call + // stackfree. + systemstack(markrootFreeGStacks) + + case work.baseSpans <= i && i < work.baseStacks: + // mark mspan.specials + markrootSpans(gcw, int(i-work.baseSpans)) + + default: + // the rest is scanning goroutine stacks + workCounter = &gcController.stackScanWork + if i < work.baseStacks || work.baseEnd <= i { + printlock() + print("runtime: markroot index ", i, " not in stack roots range [", work.baseStacks, ", ", work.baseEnd, ")\n") + throw("markroot: bad index") + } + gp := work.stackRoots[i-work.baseStacks] + + // remember when we've first observed the G blocked + // needed only to output in traceback + status := readgstatus(gp) // We are not in a scan state + if (status == _Gwaiting || status == _Gsyscall) && gp.waitsince == 0 { + gp.waitsince = work.tstart + } + + // scanstack must be done on the system stack in case + // we're trying to scan our own stack. + systemstack(func() { + // If this is a self-scan, put the user G in + // _Gwaiting to prevent self-deadlock. It may + // already be in _Gwaiting if this is a mark + // worker or we're in mark termination. + userG := getg().m.curg + selfScan := gp == userG && readgstatus(userG) == _Grunning + if selfScan { + casgstatus(userG, _Grunning, _Gwaiting) + userG.waitreason = waitReasonGarbageCollectionScan + } + + // TODO: suspendG blocks (and spins) until gp + // stops, which may take a while for + // running goroutines. Consider doing this in + // two phases where the first is non-blocking: + // we scan the stacks we can and ask running + // goroutines to scan themselves; and the + // second blocks. + stopped := suspendG(gp) + if stopped.dead { + gp.gcscandone = true + return + } + if gp.gcscandone { + throw("g already scanned") + } + workDone += scanstack(gp, gcw) + gp.gcscandone = true + resumeG(stopped) + + if selfScan { + casgstatus(userG, _Gwaiting, _Grunning) + } + }) + } + if goexperiment.PacerRedesign { + if workCounter != nil && workDone != 0 { + workCounter.Add(workDone) + if flushBgCredit { + gcFlushBgCredit(workDone) + } + } + } + return workDone +} + +// markrootBlock scans the shard'th shard of the block of memory [b0, +// b0+n0), with the given pointer mask. +// +// Returns the amount of work done. +// +//go:nowritebarrier +func markrootBlock(b0, n0 uintptr, ptrmask0 *uint8, gcw *gcWork, shard int) int64 { + if rootBlockBytes%(8*goarch.PtrSize) != 0 { + // This is necessary to pick byte offsets in ptrmask0. + throw("rootBlockBytes must be a multiple of 8*ptrSize") + } + + // Note that if b0 is toward the end of the address space, + // then b0 + rootBlockBytes might wrap around. + // These tests are written to avoid any possible overflow. + off := uintptr(shard) * rootBlockBytes + if off >= n0 { + return 0 + } + b := b0 + off + ptrmask := (*uint8)(add(unsafe.Pointer(ptrmask0), uintptr(shard)*(rootBlockBytes/(8*goarch.PtrSize)))) + n := uintptr(rootBlockBytes) + if off+n > n0 { + n = n0 - off + } + + // Scan this shard. + scanblock(b, n, ptrmask, gcw, nil) + return int64(n) +} + +// markrootFreeGStacks frees stacks of dead Gs. +// +// This does not free stacks of dead Gs cached on Ps, but having a few +// cached stacks around isn't a problem. +func markrootFreeGStacks() { + // Take list of dead Gs with stacks. + lock(&sched.gFree.lock) + list := sched.gFree.stack + sched.gFree.stack = gList{} + unlock(&sched.gFree.lock) + if list.empty() { + return + } + + // Free stacks. + q := gQueue{list.head, list.head} + for gp := list.head.ptr(); gp != nil; gp = gp.schedlink.ptr() { + stackfree(gp.stack) + gp.stack.lo = 0 + gp.stack.hi = 0 + // Manipulate the queue directly since the Gs are + // already all linked the right way. + q.tail.set(gp) + } + + // Put Gs back on the free list. + lock(&sched.gFree.lock) + sched.gFree.noStack.pushAll(q) + unlock(&sched.gFree.lock) +} + +// markrootSpans marks roots for one shard of markArenas. +// +//go:nowritebarrier +func markrootSpans(gcw *gcWork, shard int) { + // Objects with finalizers have two GC-related invariants: + // + // 1) Everything reachable from the object must be marked. + // This ensures that when we pass the object to its finalizer, + // everything the finalizer can reach will be retained. + // + // 2) Finalizer specials (which are not in the garbage + // collected heap) are roots. In practice, this means the fn + // field must be scanned. + sg := mheap_.sweepgen + + // Find the arena and page index into that arena for this shard. + ai := mheap_.markArenas[shard/(pagesPerArena/pagesPerSpanRoot)] + ha := mheap_.arenas[ai.l1()][ai.l2()] + arenaPage := uint(uintptr(shard) * pagesPerSpanRoot % pagesPerArena) + + // Construct slice of bitmap which we'll iterate over. + specialsbits := ha.pageSpecials[arenaPage/8:] + specialsbits = specialsbits[:pagesPerSpanRoot/8] + for i := range specialsbits { + // Find set bits, which correspond to spans with specials. + specials := atomic.Load8(&specialsbits[i]) + if specials == 0 { + continue + } + for j := uint(0); j < 8; j++ { + if specials&(1<<j) == 0 { + continue + } + // Find the span for this bit. + // + // This value is guaranteed to be non-nil because having + // specials implies that the span is in-use, and since we're + // currently marking we can be sure that we don't have to worry + // about the span being freed and re-used. + s := ha.spans[arenaPage+uint(i)*8+j] + + // The state must be mSpanInUse if the specials bit is set, so + // sanity check that. + if state := s.state.get(); state != mSpanInUse { + print("s.state = ", state, "\n") + throw("non in-use span found with specials bit set") + } + // Check that this span was swept (it may be cached or uncached). + if !useCheckmark && !(s.sweepgen == sg || s.sweepgen == sg+3) { + // sweepgen was updated (+2) during non-checkmark GC pass + print("sweep ", s.sweepgen, " ", sg, "\n") + throw("gc: unswept span") + } + + // Lock the specials to prevent a special from being + // removed from the list while we're traversing it. + lock(&s.speciallock) + for sp := s.specials; sp != nil; sp = sp.next { + if sp.kind != _KindSpecialFinalizer { + continue + } + // don't mark finalized object, but scan it so we + // retain everything it points to. + spf := (*specialfinalizer)(unsafe.Pointer(sp)) + // A finalizer can be set for an inner byte of an object, find object beginning. + p := s.base() + uintptr(spf.special.offset)/s.elemsize*s.elemsize + + // Mark everything that can be reached from + // the object (but *not* the object itself or + // we'll never collect it). + scanobject(p, gcw) + + // The special itself is a root. + scanblock(uintptr(unsafe.Pointer(&spf.fn)), goarch.PtrSize, &oneptrmask[0], gcw, nil) + } + unlock(&s.speciallock) + } + } +} + +// gcAssistAlloc performs GC work to make gp's assist debt positive. +// gp must be the calling user goroutine. +// +// This must be called with preemption enabled. +func gcAssistAlloc(gp *g) { + // Don't assist in non-preemptible contexts. These are + // generally fragile and won't allow the assist to block. + if getg() == gp.m.g0 { + return + } + if mp := getg().m; mp.locks > 0 || mp.preemptoff != "" { + return + } + + traced := false +retry: + // Compute the amount of scan work we need to do to make the + // balance positive. When the required amount of work is low, + // we over-assist to build up credit for future allocations + // and amortize the cost of assisting. + assistWorkPerByte := gcController.assistWorkPerByte.Load() + assistBytesPerWork := gcController.assistBytesPerWork.Load() + debtBytes := -gp.gcAssistBytes + scanWork := int64(assistWorkPerByte * float64(debtBytes)) + if scanWork < gcOverAssistWork { + scanWork = gcOverAssistWork + debtBytes = int64(assistBytesPerWork * float64(scanWork)) + } + + // Steal as much credit as we can from the background GC's + // scan credit. This is racy and may drop the background + // credit below 0 if two mutators steal at the same time. This + // will just cause steals to fail until credit is accumulated + // again, so in the long run it doesn't really matter, but we + // do have to handle the negative credit case. + bgScanCredit := atomic.Loadint64(&gcController.bgScanCredit) + stolen := int64(0) + if bgScanCredit > 0 { + if bgScanCredit < scanWork { + stolen = bgScanCredit + gp.gcAssistBytes += 1 + int64(assistBytesPerWork*float64(stolen)) + } else { + stolen = scanWork + gp.gcAssistBytes += debtBytes + } + atomic.Xaddint64(&gcController.bgScanCredit, -stolen) + + scanWork -= stolen + + if scanWork == 0 { + // We were able to steal all of the credit we + // needed. + if traced { + traceGCMarkAssistDone() + } + return + } + } + + if trace.enabled && !traced { + traced = true + traceGCMarkAssistStart() + } + + // Perform assist work + systemstack(func() { + gcAssistAlloc1(gp, scanWork) + // The user stack may have moved, so this can't touch + // anything on it until it returns from systemstack. + }) + + completed := gp.param != nil + gp.param = nil + if completed { + gcMarkDone() + } + + if gp.gcAssistBytes < 0 { + // We were unable steal enough credit or perform + // enough work to pay off the assist debt. We need to + // do one of these before letting the mutator allocate + // more to prevent over-allocation. + // + // If this is because we were preempted, reschedule + // and try some more. + if gp.preempt { + Gosched() + goto retry + } + + // Add this G to an assist queue and park. When the GC + // has more background credit, it will satisfy queued + // assists before flushing to the global credit pool. + // + // Note that this does *not* get woken up when more + // work is added to the work list. The theory is that + // there wasn't enough work to do anyway, so we might + // as well let background marking take care of the + // work that is available. + if !gcParkAssist() { + goto retry + } + + // At this point either background GC has satisfied + // this G's assist debt, or the GC cycle is over. + } + if traced { + traceGCMarkAssistDone() + } +} + +// gcAssistAlloc1 is the part of gcAssistAlloc that runs on the system +// stack. This is a separate function to make it easier to see that +// we're not capturing anything from the user stack, since the user +// stack may move while we're in this function. +// +// gcAssistAlloc1 indicates whether this assist completed the mark +// phase by setting gp.param to non-nil. This can't be communicated on +// the stack since it may move. +// +//go:systemstack +func gcAssistAlloc1(gp *g, scanWork int64) { + // Clear the flag indicating that this assist completed the + // mark phase. + gp.param = nil + + if atomic.Load(&gcBlackenEnabled) == 0 { + // The gcBlackenEnabled check in malloc races with the + // store that clears it but an atomic check in every malloc + // would be a performance hit. + // Instead we recheck it here on the non-preemptable system + // stack to determine if we should perform an assist. + + // GC is done, so ignore any remaining debt. + gp.gcAssistBytes = 0 + return + } + // Track time spent in this assist. Since we're on the + // system stack, this is non-preemptible, so we can + // just measure start and end time. + startTime := nanotime() + + decnwait := atomic.Xadd(&work.nwait, -1) + if decnwait == work.nproc { + println("runtime: work.nwait =", decnwait, "work.nproc=", work.nproc) + throw("nwait > work.nprocs") + } + + // gcDrainN requires the caller to be preemptible. + casgstatus(gp, _Grunning, _Gwaiting) + gp.waitreason = waitReasonGCAssistMarking + + // drain own cached work first in the hopes that it + // will be more cache friendly. + gcw := &getg().m.p.ptr().gcw + workDone := gcDrainN(gcw, scanWork) + + casgstatus(gp, _Gwaiting, _Grunning) + + // Record that we did this much scan work. + // + // Back out the number of bytes of assist credit that + // this scan work counts for. The "1+" is a poor man's + // round-up, to ensure this adds credit even if + // assistBytesPerWork is very low. + assistBytesPerWork := gcController.assistBytesPerWork.Load() + gp.gcAssistBytes += 1 + int64(assistBytesPerWork*float64(workDone)) + + // If this is the last worker and we ran out of work, + // signal a completion point. + incnwait := atomic.Xadd(&work.nwait, +1) + if incnwait > work.nproc { + println("runtime: work.nwait=", incnwait, + "work.nproc=", work.nproc) + throw("work.nwait > work.nproc") + } + + if incnwait == work.nproc && !gcMarkWorkAvailable(nil) { + // This has reached a background completion point. Set + // gp.param to a non-nil value to indicate this. It + // doesn't matter what we set it to (it just has to be + // a valid pointer). + gp.param = unsafe.Pointer(gp) + } + duration := nanotime() - startTime + _p_ := gp.m.p.ptr() + _p_.gcAssistTime += duration + if _p_.gcAssistTime > gcAssistTimeSlack { + atomic.Xaddint64(&gcController.assistTime, _p_.gcAssistTime) + _p_.gcAssistTime = 0 + } +} + +// gcWakeAllAssists wakes all currently blocked assists. This is used +// at the end of a GC cycle. gcBlackenEnabled must be false to prevent +// new assists from going to sleep after this point. +func gcWakeAllAssists() { + lock(&work.assistQueue.lock) + list := work.assistQueue.q.popList() + injectglist(&list) + unlock(&work.assistQueue.lock) +} + +// gcParkAssist puts the current goroutine on the assist queue and parks. +// +// gcParkAssist reports whether the assist is now satisfied. If it +// returns false, the caller must retry the assist. +func gcParkAssist() bool { + lock(&work.assistQueue.lock) + // If the GC cycle finished while we were getting the lock, + // exit the assist. The cycle can't finish while we hold the + // lock. + if atomic.Load(&gcBlackenEnabled) == 0 { + unlock(&work.assistQueue.lock) + return true + } + + gp := getg() + oldList := work.assistQueue.q + work.assistQueue.q.pushBack(gp) + + // Recheck for background credit now that this G is in + // the queue, but can still back out. This avoids a + // race in case background marking has flushed more + // credit since we checked above. + if atomic.Loadint64(&gcController.bgScanCredit) > 0 { + work.assistQueue.q = oldList + if oldList.tail != 0 { + oldList.tail.ptr().schedlink.set(nil) + } + unlock(&work.assistQueue.lock) + return false + } + // Park. + goparkunlock(&work.assistQueue.lock, waitReasonGCAssistWait, traceEvGoBlockGC, 2) + return true +} + +// gcFlushBgCredit flushes scanWork units of background scan work +// credit. This first satisfies blocked assists on the +// work.assistQueue and then flushes any remaining credit to +// gcController.bgScanCredit. +// +// Write barriers are disallowed because this is used by gcDrain after +// it has ensured that all work is drained and this must preserve that +// condition. +// +//go:nowritebarrierrec +func gcFlushBgCredit(scanWork int64) { + if work.assistQueue.q.empty() { + // Fast path; there are no blocked assists. There's a + // small window here where an assist may add itself to + // the blocked queue and park. If that happens, we'll + // just get it on the next flush. + atomic.Xaddint64(&gcController.bgScanCredit, scanWork) + return + } + + assistBytesPerWork := gcController.assistBytesPerWork.Load() + scanBytes := int64(float64(scanWork) * assistBytesPerWork) + + lock(&work.assistQueue.lock) + for !work.assistQueue.q.empty() && scanBytes > 0 { + gp := work.assistQueue.q.pop() + // Note that gp.gcAssistBytes is negative because gp + // is in debt. Think carefully about the signs below. + if scanBytes+gp.gcAssistBytes >= 0 { + // Satisfy this entire assist debt. + scanBytes += gp.gcAssistBytes + gp.gcAssistBytes = 0 + // It's important that we *not* put gp in + // runnext. Otherwise, it's possible for user + // code to exploit the GC worker's high + // scheduler priority to get itself always run + // before other goroutines and always in the + // fresh quantum started by GC. + ready(gp, 0, false) + } else { + // Partially satisfy this assist. + gp.gcAssistBytes += scanBytes + scanBytes = 0 + // As a heuristic, we move this assist to the + // back of the queue so that large assists + // can't clog up the assist queue and + // substantially delay small assists. + work.assistQueue.q.pushBack(gp) + break + } + } + + if scanBytes > 0 { + // Convert from scan bytes back to work. + assistWorkPerByte := gcController.assistWorkPerByte.Load() + scanWork = int64(float64(scanBytes) * assistWorkPerByte) + atomic.Xaddint64(&gcController.bgScanCredit, scanWork) + } + unlock(&work.assistQueue.lock) +} + +// scanstack scans gp's stack, greying all pointers found on the stack. +// +// For goexperiment.PacerRedesign: +// Returns the amount of scan work performed, but doesn't update +// gcController.stackScanWork or flush any credit. Any background credit produced +// by this function should be flushed by its caller. scanstack itself can't +// safely flush because it may result in trying to wake up a goroutine that +// was just scanned, resulting in a self-deadlock. +// +// scanstack will also shrink the stack if it is safe to do so. If it +// is not, it schedules a stack shrink for the next synchronous safe +// point. +// +// scanstack is marked go:systemstack because it must not be preempted +// while using a workbuf. +// +//go:nowritebarrier +//go:systemstack +func scanstack(gp *g, gcw *gcWork) int64 { + if readgstatus(gp)&_Gscan == 0 { + print("runtime:scanstack: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", hex(readgstatus(gp)), "\n") + throw("scanstack - bad status") + } + + switch readgstatus(gp) &^ _Gscan { + default: + print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n") + throw("mark - bad status") + case _Gdead: + return 0 + case _Grunning: + print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n") + throw("scanstack: goroutine not stopped") + case _Grunnable, _Gsyscall, _Gwaiting: + // ok + } + + if gp == getg() { + throw("can't scan our own stack") + } + + // stackSize is the amount of work we'll be reporting. + // + // We report the total stack size, more than we scan, + // because this number needs to line up with gcControllerState's + // stackScan and scannableStackSize fields. + // + // See the documentation on those fields for more information. + stackSize := gp.stack.hi - gp.stack.lo + + if isShrinkStackSafe(gp) { + // Shrink the stack if not much of it is being used. + shrinkstack(gp) + } else { + // Otherwise, shrink the stack at the next sync safe point. + gp.preemptShrink = true + } + + var state stackScanState + state.stack = gp.stack + + if stackTraceDebug { + println("stack trace goroutine", gp.goid) + } + + if debugScanConservative && gp.asyncSafePoint { + print("scanning async preempted goroutine ", gp.goid, " stack [", hex(gp.stack.lo), ",", hex(gp.stack.hi), ")\n") + } + + // Scan the saved context register. This is effectively a live + // register that gets moved back and forth between the + // register and sched.ctxt without a write barrier. + if gp.sched.ctxt != nil { + scanblock(uintptr(unsafe.Pointer(&gp.sched.ctxt)), goarch.PtrSize, &oneptrmask[0], gcw, &state) + } + + // Scan the stack. Accumulate a list of stack objects. + scanframe := func(frame *stkframe, unused unsafe.Pointer) bool { + scanframeworker(frame, &state, gcw) + return true + } + gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, scanframe, nil, 0) + + // Find additional pointers that point into the stack from the heap. + // Currently this includes defers and panics. See also function copystack. + + // Find and trace other pointers in defer records. + for d := gp._defer; d != nil; d = d.link { + if d.fn != nil { + // Scan the func value, which could be a stack allocated closure. + // See issue 30453. + scanblock(uintptr(unsafe.Pointer(&d.fn)), goarch.PtrSize, &oneptrmask[0], gcw, &state) + } + if d.link != nil { + // The link field of a stack-allocated defer record might point + // to a heap-allocated defer record. Keep that heap record live. + scanblock(uintptr(unsafe.Pointer(&d.link)), goarch.PtrSize, &oneptrmask[0], gcw, &state) + } + // Retain defers records themselves. + // Defer records might not be reachable from the G through regular heap + // tracing because the defer linked list might weave between the stack and the heap. + if d.heap { + scanblock(uintptr(unsafe.Pointer(&d)), goarch.PtrSize, &oneptrmask[0], gcw, &state) + } + } + if gp._panic != nil { + // Panics are always stack allocated. + state.putPtr(uintptr(unsafe.Pointer(gp._panic)), false) + } + + // Find and scan all reachable stack objects. + // + // The state's pointer queue prioritizes precise pointers over + // conservative pointers so that we'll prefer scanning stack + // objects precisely. + state.buildIndex() + for { + p, conservative := state.getPtr() + if p == 0 { + break + } + obj := state.findObject(p) + if obj == nil { + continue + } + r := obj.r + if r == nil { + // We've already scanned this object. + continue + } + obj.setRecord(nil) // Don't scan it again. + if stackTraceDebug { + printlock() + print(" live stkobj at", hex(state.stack.lo+uintptr(obj.off)), "of size", obj.size) + if conservative { + print(" (conservative)") + } + println() + printunlock() + } + gcdata := r.gcdata() + var s *mspan + if r.useGCProg() { + // This path is pretty unlikely, an object large enough + // to have a GC program allocated on the stack. + // We need some space to unpack the program into a straight + // bitmask, which we allocate/free here. + // TODO: it would be nice if there were a way to run a GC + // program without having to store all its bits. We'd have + // to change from a Lempel-Ziv style program to something else. + // Or we can forbid putting objects on stacks if they require + // a gc program (see issue 27447). + s = materializeGCProg(r.ptrdata(), gcdata) + gcdata = (*byte)(unsafe.Pointer(s.startAddr)) + } + + b := state.stack.lo + uintptr(obj.off) + if conservative { + scanConservative(b, r.ptrdata(), gcdata, gcw, &state) + } else { + scanblock(b, r.ptrdata(), gcdata, gcw, &state) + } + + if s != nil { + dematerializeGCProg(s) + } + } + + // Deallocate object buffers. + // (Pointer buffers were all deallocated in the loop above.) + for state.head != nil { + x := state.head + state.head = x.next + if stackTraceDebug { + for i := 0; i < x.nobj; i++ { + obj := &x.obj[i] + if obj.r == nil { // reachable + continue + } + println(" dead stkobj at", hex(gp.stack.lo+uintptr(obj.off)), "of size", obj.r.size) + // Note: not necessarily really dead - only reachable-from-ptr dead. + } + } + x.nobj = 0 + putempty((*workbuf)(unsafe.Pointer(x))) + } + if state.buf != nil || state.cbuf != nil || state.freeBuf != nil { + throw("remaining pointer buffers") + } + return int64(stackSize) +} + +// Scan a stack frame: local variables and function arguments/results. +//go:nowritebarrier +func scanframeworker(frame *stkframe, state *stackScanState, gcw *gcWork) { + if _DebugGC > 1 && frame.continpc != 0 { + print("scanframe ", funcname(frame.fn), "\n") + } + + isAsyncPreempt := frame.fn.valid() && frame.fn.funcID == funcID_asyncPreempt + isDebugCall := frame.fn.valid() && frame.fn.funcID == funcID_debugCallV2 + if state.conservative || isAsyncPreempt || isDebugCall { + if debugScanConservative { + println("conservatively scanning function", funcname(frame.fn), "at PC", hex(frame.continpc)) + } + + // Conservatively scan the frame. Unlike the precise + // case, this includes the outgoing argument space + // since we may have stopped while this function was + // setting up a call. + // + // TODO: We could narrow this down if the compiler + // produced a single map per function of stack slots + // and registers that ever contain a pointer. + if frame.varp != 0 { + size := frame.varp - frame.sp + if size > 0 { + scanConservative(frame.sp, size, nil, gcw, state) + } + } + + // Scan arguments to this frame. + if frame.arglen != 0 { + // TODO: We could pass the entry argument map + // to narrow this down further. + scanConservative(frame.argp, frame.arglen, nil, gcw, state) + } + + if isAsyncPreempt || isDebugCall { + // This function's frame contained the + // registers for the asynchronously stopped + // parent frame. Scan the parent + // conservatively. + state.conservative = true + } else { + // We only wanted to scan those two frames + // conservatively. Clear the flag for future + // frames. + state.conservative = false + } + return + } + + locals, args, objs := getStackMap(frame, &state.cache, false) + + // Scan local variables if stack frame has been allocated. + if locals.n > 0 { + size := uintptr(locals.n) * goarch.PtrSize + scanblock(frame.varp-size, size, locals.bytedata, gcw, state) + } + + // Scan arguments. + if args.n > 0 { + scanblock(frame.argp, uintptr(args.n)*goarch.PtrSize, args.bytedata, gcw, state) + } + + // Add all stack objects to the stack object list. + if frame.varp != 0 { + // varp is 0 for defers, where there are no locals. + // In that case, there can't be a pointer to its args, either. + // (And all args would be scanned above anyway.) + for i := range objs { + obj := &objs[i] + off := obj.off + base := frame.varp // locals base pointer + if off >= 0 { + base = frame.argp // arguments and return values base pointer + } + ptr := base + uintptr(off) + if ptr < frame.sp { + // object hasn't been allocated in the frame yet. + continue + } + if stackTraceDebug { + println("stkobj at", hex(ptr), "of size", obj.size) + } + state.addObject(ptr, obj) + } + } +} + +type gcDrainFlags int + +const ( + gcDrainUntilPreempt gcDrainFlags = 1 << iota + gcDrainFlushBgCredit + gcDrainIdle + gcDrainFractional +) + +// gcDrain scans roots and objects in work buffers, blackening grey +// objects until it is unable to get more work. It may return before +// GC is done; it's the caller's responsibility to balance work from +// other Ps. +// +// If flags&gcDrainUntilPreempt != 0, gcDrain returns when g.preempt +// is set. +// +// If flags&gcDrainIdle != 0, gcDrain returns when there is other work +// to do. +// +// If flags&gcDrainFractional != 0, gcDrain self-preempts when +// pollFractionalWorkerExit() returns true. This implies +// gcDrainNoBlock. +// +// If flags&gcDrainFlushBgCredit != 0, gcDrain flushes scan work +// credit to gcController.bgScanCredit every gcCreditSlack units of +// scan work. +// +// gcDrain will always return if there is a pending STW. +// +//go:nowritebarrier +func gcDrain(gcw *gcWork, flags gcDrainFlags) { + if !writeBarrier.needed { + throw("gcDrain phase incorrect") + } + + gp := getg().m.curg + preemptible := flags&gcDrainUntilPreempt != 0 + flushBgCredit := flags&gcDrainFlushBgCredit != 0 + idle := flags&gcDrainIdle != 0 + + initScanWork := gcw.heapScanWork + + // checkWork is the scan work before performing the next + // self-preempt check. + checkWork := int64(1<<63 - 1) + var check func() bool + if flags&(gcDrainIdle|gcDrainFractional) != 0 { + checkWork = initScanWork + drainCheckThreshold + if idle { + check = pollWork + } else if flags&gcDrainFractional != 0 { + check = pollFractionalWorkerExit + } + } + + // Drain root marking jobs. + if work.markrootNext < work.markrootJobs { + // Stop if we're preemptible or if someone wants to STW. + for !(gp.preempt && (preemptible || atomic.Load(&sched.gcwaiting) != 0)) { + job := atomic.Xadd(&work.markrootNext, +1) - 1 + if job >= work.markrootJobs { + break + } + markroot(gcw, job, flushBgCredit) + if check != nil && check() { + goto done + } + } + } + + // Drain heap marking jobs. + // Stop if we're preemptible or if someone wants to STW. + for !(gp.preempt && (preemptible || atomic.Load(&sched.gcwaiting) != 0)) { + // Try to keep work available on the global queue. We used to + // check if there were waiting workers, but it's better to + // just keep work available than to make workers wait. In the + // worst case, we'll do O(log(_WorkbufSize)) unnecessary + // balances. + if work.full == 0 { + gcw.balance() + } + + b := gcw.tryGetFast() + if b == 0 { + b = gcw.tryGet() + if b == 0 { + // Flush the write barrier + // buffer; this may create + // more work. + wbBufFlush(nil, 0) + b = gcw.tryGet() + } + } + if b == 0 { + // Unable to get work. + break + } + scanobject(b, gcw) + + // Flush background scan work credit to the global + // account if we've accumulated enough locally so + // mutator assists can draw on it. + if gcw.heapScanWork >= gcCreditSlack { + gcController.heapScanWork.Add(gcw.heapScanWork) + if flushBgCredit { + gcFlushBgCredit(gcw.heapScanWork - initScanWork) + initScanWork = 0 + } + checkWork -= gcw.heapScanWork + gcw.heapScanWork = 0 + + if checkWork <= 0 { + checkWork += drainCheckThreshold + if check != nil && check() { + break + } + } + } + } + +done: + // Flush remaining scan work credit. + if gcw.heapScanWork > 0 { + gcController.heapScanWork.Add(gcw.heapScanWork) + if flushBgCredit { + gcFlushBgCredit(gcw.heapScanWork - initScanWork) + } + gcw.heapScanWork = 0 + } +} + +// gcDrainN blackens grey objects until it has performed roughly +// scanWork units of scan work or the G is preempted. This is +// best-effort, so it may perform less work if it fails to get a work +// buffer. Otherwise, it will perform at least n units of work, but +// may perform more because scanning is always done in whole object +// increments. It returns the amount of scan work performed. +// +// The caller goroutine must be in a preemptible state (e.g., +// _Gwaiting) to prevent deadlocks during stack scanning. As a +// consequence, this must be called on the system stack. +// +//go:nowritebarrier +//go:systemstack +func gcDrainN(gcw *gcWork, scanWork int64) int64 { + if !writeBarrier.needed { + throw("gcDrainN phase incorrect") + } + + // There may already be scan work on the gcw, which we don't + // want to claim was done by this call. + workFlushed := -gcw.heapScanWork + + gp := getg().m.curg + for !gp.preempt && workFlushed+gcw.heapScanWork < scanWork { + // See gcDrain comment. + if work.full == 0 { + gcw.balance() + } + + b := gcw.tryGetFast() + if b == 0 { + b = gcw.tryGet() + if b == 0 { + // Flush the write barrier buffer; + // this may create more work. + wbBufFlush(nil, 0) + b = gcw.tryGet() + } + } + + if b == 0 { + // Try to do a root job. + if work.markrootNext < work.markrootJobs { + job := atomic.Xadd(&work.markrootNext, +1) - 1 + if job < work.markrootJobs { + work := markroot(gcw, job, false) + if goexperiment.PacerRedesign { + workFlushed += work + } + continue + } + } + // No heap or root jobs. + break + } + + scanobject(b, gcw) + + // Flush background scan work credit. + if gcw.heapScanWork >= gcCreditSlack { + gcController.heapScanWork.Add(gcw.heapScanWork) + workFlushed += gcw.heapScanWork + gcw.heapScanWork = 0 + } + } + + // Unlike gcDrain, there's no need to flush remaining work + // here because this never flushes to bgScanCredit and + // gcw.dispose will flush any remaining work to scanWork. + + return workFlushed + gcw.heapScanWork +} + +// scanblock scans b as scanobject would, but using an explicit +// pointer bitmap instead of the heap bitmap. +// +// This is used to scan non-heap roots, so it does not update +// gcw.bytesMarked or gcw.heapScanWork. +// +// If stk != nil, possible stack pointers are also reported to stk.putPtr. +//go:nowritebarrier +func scanblock(b0, n0 uintptr, ptrmask *uint8, gcw *gcWork, stk *stackScanState) { + // Use local copies of original parameters, so that a stack trace + // due to one of the throws below shows the original block + // base and extent. + b := b0 + n := n0 + + for i := uintptr(0); i < n; { + // Find bits for the next word. + bits := uint32(*addb(ptrmask, i/(goarch.PtrSize*8))) + if bits == 0 { + i += goarch.PtrSize * 8 + continue + } + for j := 0; j < 8 && i < n; j++ { + if bits&1 != 0 { + // Same work as in scanobject; see comments there. + p := *(*uintptr)(unsafe.Pointer(b + i)) + if p != 0 { + if obj, span, objIndex := findObject(p, b, i); obj != 0 { + greyobject(obj, b, i, span, gcw, objIndex) + } else if stk != nil && p >= stk.stack.lo && p < stk.stack.hi { + stk.putPtr(p, false) + } + } + } + bits >>= 1 + i += goarch.PtrSize + } + } +} + +// scanobject scans the object starting at b, adding pointers to gcw. +// b must point to the beginning of a heap object or an oblet. +// scanobject consults the GC bitmap for the pointer mask and the +// spans for the size of the object. +// +//go:nowritebarrier +func scanobject(b uintptr, gcw *gcWork) { + // Prefetch object before we scan it. + // + // This will overlap fetching the beginning of the object with initial + // setup before we start scanning the object. + sys.Prefetch(b) + + // Find the bits for b and the size of the object at b. + // + // b is either the beginning of an object, in which case this + // is the size of the object to scan, or it points to an + // oblet, in which case we compute the size to scan below. + hbits := heapBitsForAddr(b) + s := spanOfUnchecked(b) + n := s.elemsize + if n == 0 { + throw("scanobject n == 0") + } + + if n > maxObletBytes { + // Large object. Break into oblets for better + // parallelism and lower latency. + if b == s.base() { + // It's possible this is a noscan object (not + // from greyobject, but from other code + // paths), in which case we must *not* enqueue + // oblets since their bitmaps will be + // uninitialized. + if s.spanclass.noscan() { + // Bypass the whole scan. + gcw.bytesMarked += uint64(n) + return + } + + // Enqueue the other oblets to scan later. + // Some oblets may be in b's scalar tail, but + // these will be marked as "no more pointers", + // so we'll drop out immediately when we go to + // scan those. + for oblet := b + maxObletBytes; oblet < s.base()+s.elemsize; oblet += maxObletBytes { + if !gcw.putFast(oblet) { + gcw.put(oblet) + } + } + } + + // Compute the size of the oblet. Since this object + // must be a large object, s.base() is the beginning + // of the object. + n = s.base() + s.elemsize - b + if n > maxObletBytes { + n = maxObletBytes + } + } + + var i uintptr + for i = 0; i < n; i, hbits = i+goarch.PtrSize, hbits.next() { + // Load bits once. See CL 22712 and issue 16973 for discussion. + bits := hbits.bits() + if bits&bitScan == 0 { + break // no more pointers in this object + } + if bits&bitPointer == 0 { + continue // not a pointer + } + + // Work here is duplicated in scanblock and above. + // If you make changes here, make changes there too. + obj := *(*uintptr)(unsafe.Pointer(b + i)) + + // At this point we have extracted the next potential pointer. + // Quickly filter out nil and pointers back to the current object. + if obj != 0 && obj-b >= n { + // Test if obj points into the Go heap and, if so, + // mark the object. + // + // Note that it's possible for findObject to + // fail if obj points to a just-allocated heap + // object because of a race with growing the + // heap. In this case, we know the object was + // just allocated and hence will be marked by + // allocation itself. + if obj, span, objIndex := findObject(obj, b, i); obj != 0 { + greyobject(obj, b, i, span, gcw, objIndex) + } + } + } + gcw.bytesMarked += uint64(n) + gcw.heapScanWork += int64(i) +} + +// scanConservative scans block [b, b+n) conservatively, treating any +// pointer-like value in the block as a pointer. +// +// If ptrmask != nil, only words that are marked in ptrmask are +// considered as potential pointers. +// +// If state != nil, it's assumed that [b, b+n) is a block in the stack +// and may contain pointers to stack objects. +func scanConservative(b, n uintptr, ptrmask *uint8, gcw *gcWork, state *stackScanState) { + if debugScanConservative { + printlock() + print("conservatively scanning [", hex(b), ",", hex(b+n), ")\n") + hexdumpWords(b, b+n, func(p uintptr) byte { + if ptrmask != nil { + word := (p - b) / goarch.PtrSize + bits := *addb(ptrmask, word/8) + if (bits>>(word%8))&1 == 0 { + return '$' + } + } + + val := *(*uintptr)(unsafe.Pointer(p)) + if state != nil && state.stack.lo <= val && val < state.stack.hi { + return '@' + } + + span := spanOfHeap(val) + if span == nil { + return ' ' + } + idx := span.objIndex(val) + if span.isFree(idx) { + return ' ' + } + return '*' + }) + printunlock() + } + + for i := uintptr(0); i < n; i += goarch.PtrSize { + if ptrmask != nil { + word := i / goarch.PtrSize + bits := *addb(ptrmask, word/8) + if bits == 0 { + // Skip 8 words (the loop increment will do the 8th) + // + // This must be the first time we've + // seen this word of ptrmask, so i + // must be 8-word-aligned, but check + // our reasoning just in case. + if i%(goarch.PtrSize*8) != 0 { + throw("misaligned mask") + } + i += goarch.PtrSize*8 - goarch.PtrSize + continue + } + if (bits>>(word%8))&1 == 0 { + continue + } + } + + val := *(*uintptr)(unsafe.Pointer(b + i)) + + // Check if val points into the stack. + if state != nil && state.stack.lo <= val && val < state.stack.hi { + // val may point to a stack object. This + // object may be dead from last cycle and + // hence may contain pointers to unallocated + // objects, but unlike heap objects we can't + // tell if it's already dead. Hence, if all + // pointers to this object are from + // conservative scanning, we have to scan it + // defensively, too. + state.putPtr(val, true) + continue + } + + // Check if val points to a heap span. + span := spanOfHeap(val) + if span == nil { + continue + } + + // Check if val points to an allocated object. + idx := span.objIndex(val) + if span.isFree(idx) { + continue + } + + // val points to an allocated object. Mark it. + obj := span.base() + idx*span.elemsize + greyobject(obj, b, i, span, gcw, idx) + } +} + +// Shade the object if it isn't already. +// The object is not nil and known to be in the heap. +// Preemption must be disabled. +//go:nowritebarrier +func shade(b uintptr) { + if obj, span, objIndex := findObject(b, 0, 0); obj != 0 { + gcw := &getg().m.p.ptr().gcw + greyobject(obj, 0, 0, span, gcw, objIndex) + } +} + +// obj is the start of an object with mark mbits. +// If it isn't already marked, mark it and enqueue into gcw. +// base and off are for debugging only and could be removed. +// +// See also wbBufFlush1, which partially duplicates this logic. +// +//go:nowritebarrierrec +func greyobject(obj, base, off uintptr, span *mspan, gcw *gcWork, objIndex uintptr) { + // obj should be start of allocation, and so must be at least pointer-aligned. + if obj&(goarch.PtrSize-1) != 0 { + throw("greyobject: obj not pointer-aligned") + } + mbits := span.markBitsForIndex(objIndex) + + if useCheckmark { + if setCheckmark(obj, base, off, mbits) { + // Already marked. + return + } + } else { + if debug.gccheckmark > 0 && span.isFree(objIndex) { + print("runtime: marking free object ", hex(obj), " found at *(", hex(base), "+", hex(off), ")\n") + gcDumpObject("base", base, off) + gcDumpObject("obj", obj, ^uintptr(0)) + getg().m.traceback = 2 + throw("marking free object") + } + + // If marked we have nothing to do. + if mbits.isMarked() { + return + } + mbits.setMarked() + + // Mark span. + arena, pageIdx, pageMask := pageIndexOf(span.base()) + if arena.pageMarks[pageIdx]&pageMask == 0 { + atomic.Or8(&arena.pageMarks[pageIdx], pageMask) + } + + // If this is a noscan object, fast-track it to black + // instead of greying it. + if span.spanclass.noscan() { + gcw.bytesMarked += uint64(span.elemsize) + return + } + } + + // We're adding obj to P's local workbuf, so it's likely + // this object will be processed soon by the same P. + // Even if the workbuf gets flushed, there will likely still be + // some benefit on platforms with inclusive shared caches. + sys.Prefetch(obj) + // Queue the obj for scanning. + if !gcw.putFast(obj) { + gcw.put(obj) + } +} + +// gcDumpObject dumps the contents of obj for debugging and marks the +// field at byte offset off in obj. +func gcDumpObject(label string, obj, off uintptr) { + s := spanOf(obj) + print(label, "=", hex(obj)) + if s == nil { + print(" s=nil\n") + return + } + print(" s.base()=", hex(s.base()), " s.limit=", hex(s.limit), " s.spanclass=", s.spanclass, " s.elemsize=", s.elemsize, " s.state=") + if state := s.state.get(); 0 <= state && int(state) < len(mSpanStateNames) { + print(mSpanStateNames[state], "\n") + } else { + print("unknown(", state, ")\n") + } + + skipped := false + size := s.elemsize + if s.state.get() == mSpanManual && size == 0 { + // We're printing something from a stack frame. We + // don't know how big it is, so just show up to an + // including off. + size = off + goarch.PtrSize + } + for i := uintptr(0); i < size; i += goarch.PtrSize { + // For big objects, just print the beginning (because + // that usually hints at the object's type) and the + // fields around off. + if !(i < 128*goarch.PtrSize || off-16*goarch.PtrSize < i && i < off+16*goarch.PtrSize) { + skipped = true + continue + } + if skipped { + print(" ...\n") + skipped = false + } + print(" *(", label, "+", i, ") = ", hex(*(*uintptr)(unsafe.Pointer(obj + i)))) + if i == off { + print(" <==") + } + print("\n") + } + if skipped { + print(" ...\n") + } +} + +// gcmarknewobject marks a newly allocated object black. obj must +// not contain any non-nil pointers. +// +// This is nosplit so it can manipulate a gcWork without preemption. +// +//go:nowritebarrier +//go:nosplit +func gcmarknewobject(span *mspan, obj, size, scanSize uintptr) { + if useCheckmark { // The world should be stopped so this should not happen. + throw("gcmarknewobject called while doing checkmark") + } + + // Mark object. + objIndex := span.objIndex(obj) + span.markBitsForIndex(objIndex).setMarked() + + // Mark span. + arena, pageIdx, pageMask := pageIndexOf(span.base()) + if arena.pageMarks[pageIdx]&pageMask == 0 { + atomic.Or8(&arena.pageMarks[pageIdx], pageMask) + } + + gcw := &getg().m.p.ptr().gcw + gcw.bytesMarked += uint64(size) + if !goexperiment.PacerRedesign { + // The old pacer counts newly allocated memory toward + // heapScanWork because heapScan is continuously updated + // throughout the GC cycle with newly allocated memory. However, + // these objects are never actually scanned, so we need + // to account for them in heapScanWork here, "faking" their work. + // Otherwise the pacer will think it's always behind, potentially + // by a large margin. + // + // The new pacer doesn't care about this because it ceases to updated + // heapScan once a GC cycle starts, effectively snapshotting it. + gcw.heapScanWork += int64(scanSize) + } +} + +// gcMarkTinyAllocs greys all active tiny alloc blocks. +// +// The world must be stopped. +func gcMarkTinyAllocs() { + assertWorldStopped() + + for _, p := range allp { + c := p.mcache + if c == nil || c.tiny == 0 { + continue + } + _, span, objIndex := findObject(c.tiny, 0, 0) + gcw := &p.gcw + greyobject(c.tiny, 0, 0, span, gcw, objIndex) + } +} |