golang mgcmark 代码
文件路径：/src/runtime/mgcmark.go
/ 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"
"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 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:
if go119MemoryLimitSupport && gcCPULimiter.limiting() {
/ If the CPU limiter is enabled, intentionally don't
/ assist to reduce the amount of CPU time spent in the GC.
if traced {
traceGCMarkAssistDone()
}
return
}
/ 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.
/
/ Limiter event tracking might be disabled if we end up here
/ while on a mark worker.
startTime := nanotime()
trackLimiterEvent := gp.m.p.ptr().limiterEvent.start(limiterEventMarkAssist, startTime)
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)
}
now := nanotime()
duration := now - startTime
_p_ := gp.m.p.ptr()
_p_.gcAssistTime += duration
if trackLimiterEvent {
_p_.limiterEvent.stop(limiterEventMarkAssist, now)
}
if _p_.gcAssistTime > gcAssistTimeSlack {
gcController.assistTime.Add(_p_.gcAssistTime)
gcCPULimiter.update(now)
_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.
/
/ 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")
}
/ scannedSize is the amount of work we'll be reporting.
/
/ It is less than the allocated size (which is hi-lo).
var sp uintptr
if gp.syscallsp != 0 {
sp = gp.syscallsp / If in a system call this is the stack pointer (gp.sched.sp can be 0 in this case on Windows).
} else {
sp = gp.sched.sp
}
scannedSize := gp.stack.hi - sp
/ Keep statistics for initial stack size calculation.
/ Note that this accumulates the scanned size, not the allocated size.
p := getg().m.p.ptr()
p.scannedStackSize += uint64(scannedSize)
p.scannedStacks++
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(scannedSize)
}
/ 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
/ In addition to backing out because of a preemption, back out
/ if the GC CPU limiter is enabled.
gp := getg().m.curg
for !gp.preempt && !gcCPULimiter.limiting() && 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 {
workFlushed += markroot(gcw, job, false)
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)
}
/ 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)
}
}