Newer
Older
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
// the amount of potentially wasted memory is bounded.
//
// Size of the memory block used for combining (maxTinySize) is tunable.
// Current setting is 16 bytes, which relates to 2x worst case memory
// wastage (when all but one subobjects are unreachable).
// 8 bytes would result in no wastage at all, but provides less
// opportunities for combining.
// 32 bytes provides more opportunities for combining,
// but can lead to 4x worst case wastage.
// The best case winning is 8x regardless of block size.
//
// Objects obtained from tiny allocator must not be freed explicitly.
// So when an object will be freed explicitly, we ensure that
// its size >= maxTinySize.
//
// SetFinalizer has a special case for objects potentially coming
// from tiny allocator, it such case it allows to set finalizers
// for an inner byte of a memory block.
//
// The main targets of tiny allocator are small strings and
// standalone escaping variables. On a json benchmark
// the allocator reduces number of allocations by ~12% and
// reduces heap size by ~20%.
off := c.tinyoffset
// Align tiny pointer for required (conservative) alignment.
if size&7 == 0 {
off = alignUp(off, 8)
Michael Anthony Knyszek
committed
} else if goarch.PtrSize == 4 && size == 12 {
// Conservatively align 12-byte objects to 8 bytes on 32-bit
// systems so that objects whose first field is a 64-bit
// value is aligned to 8 bytes and does not cause a fault on
// atomic access. See issue 37262.
// TODO(mknyszek): Remove this workaround if/when issue 36606
// is resolved.
off = alignUp(off, 8)
} else if size&3 == 0 {
off = alignUp(off, 4)
} else if size&1 == 0 {
off = alignUp(off, 2)
}
if off+size <= maxTinySize && c.tiny != 0 {
// The object fits into existing tiny block.
c.tinyoffset = off + size
c.tinyAllocs++
mp.mallocing = 0
releasem(mp)
return x
}
// Allocate a new maxTinySize block.
span = c.alloc[tinySpanClass]
v := nextFreeFast(span)
v, span, shouldhelpgc = c.nextFree(tinySpanClass)
x = unsafe.Pointer(v)
(*[2]uint64)(x)[0] = 0
(*[2]uint64)(x)[1] = 0
// See if we need to replace the existing tiny block with the new one
// based on amount of remaining free space.
if !raceenabled && (size < c.tinyoffset || c.tiny == 0) {
// Note: disabled when race detector is on, see comment near end of this function.
c.tinyoffset = size
var sizeclass uint8
if size <= smallSizeMax-8 {
sizeclass = size_to_class8[divRoundUp(size, smallSizeDiv)]
sizeclass = size_to_class128[divRoundUp(size-smallSizeMax, largeSizeDiv)]
}
size = uintptr(class_to_size[sizeclass])
spc := makeSpanClass(sizeclass, noscan)
v := nextFreeFast(span)
v, span, shouldhelpgc = c.nextFree(spc)
if needzero && span.needzero != 0 {
memclrNoHeapPointers(unsafe.Pointer(v), size)
// For large allocations, keep track of zeroed state so that
// bulk zeroing can be happen later in a preemptible context.
span = c.allocLarge(size, noscan)
span.freeindex = 1
span.allocCount = 1
size = span.elemsize
x = unsafe.Pointer(span.base())
if needzero && span.needzero != 0 {
if noscan {
delayedZeroing = true
} else {
memclrNoHeapPointers(x, size)
// We've in theory cleared almost the whole span here,
// and could take the extra step of actually clearing
// the whole thing. However, don't. Any GC bits for the
// uncleared parts will be zero, and it's just going to
// be needzero = 1 once freed anyway.
}
}
var scanSize uintptr
heapBitsSetType(uintptr(x), size, dataSize, typ)
if dataSize > typ.size {
// Array allocation. If there are any
// pointers, GC has to scan to the last
// element.
if typ.ptrdata != 0 {
scanSize = dataSize - typ.size + typ.ptrdata
scanSize = typ.ptrdata
c.scanAlloc += scanSize
// Ensure that the stores above that initialize x to
// type-safe memory and set the heap bits occur before
// the caller can make x observable to the garbage
// collector. Otherwise, on weakly ordered machines,
// the garbage collector could follow a pointer to x,
// but see uninitialized memory or stale heap bits.
publicationBarrier()
// All slots hold nil so no scanning is needed.
// This may be racing with GC so do it atomically if there can be
// a race marking the bit.
gcmarknewobject(span, uintptr(x), size, scanSize)
if raceenabled {
racemalloc(x, size)
}
if msanenabled {
msanmalloc(x, size)
}
if asanenabled {
// We should only read/write the memory with the size asked by the user.
// The rest of the allocated memory should be poisoned, so that we can report
// errors when accessing poisoned memory.
// The allocated memory is larger than required userSize, it will also include
// redzone and some other padding bytes.
rzBeg := unsafe.Add(x, userSize)
asanpoison(rzBeg, size-userSize)
asanunpoison(x, userSize)
}
if rate := MemProfileRate; rate > 0 {
// Note cache c only valid while m acquired; see #47302
if rate != 1 && size < c.nextSample {
c.nextSample -= size
} else {
profilealloc(mp, x, size)
}
}
mp.mallocing = 0
releasem(mp)
// Pointerfree data can be zeroed late in a context where preemption can occur.
// x will keep the memory alive.
if delayedZeroing {
if !noscan {
throw("delayed zeroing on data that may contain pointers")
}
memclrNoHeapPointersChunked(size, x) // This is a possible preemption point: see #47302
}
if debug.malloc {
if debug.allocfreetrace != 0 {
tracealloc(x, size, typ)
}
if inittrace.active && inittrace.id == getg().goid {
// Init functions are executed sequentially in a single goroutine.
inittrace.bytes += uint64(size)
}
if assistG != nil {
// Account for internal fragmentation in the assist
// debt now that we know it.
assistG.gcAssistBytes -= int64(size - dataSize)
}
if shouldhelpgc {
if t := (gcTrigger{kind: gcTriggerHeap}); t.test() {
if raceenabled && noscan && dataSize < maxTinySize {
// Pad tinysize allocations so they are aligned with the end
// of the tinyalloc region. This ensures that any arithmetic
// that goes off the top end of the object will be detectable
// by checkptr (issue 38872).
// Note that we disable tinyalloc when raceenabled for this to work.
// TODO: This padding is only performed when the race detector
// is enabled. It would be nice to enable it if any package
// was compiled with checkptr, but there's no easy way to
// detect that (especially at compile time).
// TODO: enable this padding for all allocations, not just
// tinyalloc ones. It's tricky because of pointer maps.
// Maybe just all noscan objects?
x = add(x, size-dataSize)
}
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
// memclrNoHeapPointersChunked repeatedly calls memclrNoHeapPointers
// on chunks of the buffer to be zeroed, with opportunities for preemption
// along the way. memclrNoHeapPointers contains no safepoints and also
// cannot be preemptively scheduled, so this provides a still-efficient
// block copy that can also be preempted on a reasonable granularity.
//
// Use this with care; if the data being cleared is tagged to contain
// pointers, this allows the GC to run before it is all cleared.
func memclrNoHeapPointersChunked(size uintptr, x unsafe.Pointer) {
v := uintptr(x)
// got this from benchmarking. 128k is too small, 512k is too large.
const chunkBytes = 256 * 1024
vsize := v + size
for voff := v; voff < vsize; voff = voff + chunkBytes {
if getg().preempt {
// may hold locks, e.g., profiling
goschedguarded()
}
// clear min(avail, lump) bytes
n := vsize - voff
if n > chunkBytes {
n = chunkBytes
}
memclrNoHeapPointers(unsafe.Pointer(voff), n)
}
}
// compiler (both frontend and SSA backend) knows the signature
// of this function
func newobject(typ *_type) unsafe.Pointer {
return mallocgc(typ.size, typ, true)
//go:linkname reflect_unsafe_New reflect.unsafe_New
func reflect_unsafe_New(typ *_type) unsafe.Pointer {
return mallocgc(typ.size, typ, true)
//go:linkname reflectlite_unsafe_New internal/reflectlite.unsafe_New
func reflectlite_unsafe_New(typ *_type) unsafe.Pointer {
return mallocgc(typ.size, typ, true)
}
// newarray allocates an array of n elements of type typ.
func newarray(typ *_type, n int) unsafe.Pointer {
if n == 1 {
return mallocgc(typ.size, typ, true)
}
mem, overflow := math.MulUintptr(typ.size, uintptr(n))
if overflow || mem > maxAlloc || n < 0 {
panic(plainError("runtime: allocation size out of range"))
return mallocgc(mem, typ, true)
//go:linkname reflect_unsafe_NewArray reflect.unsafe_NewArray
func reflect_unsafe_NewArray(typ *_type, n int) unsafe.Pointer {
func profilealloc(mp *m, x unsafe.Pointer, size uintptr) {
if c == nil {
throw("profilealloc called without a P or outside bootstrapping")
}
c.nextSample = nextSample()
// nextSample returns the next sampling point for heap profiling. The goal is
// to sample allocations on average every MemProfileRate bytes, but with a
// completely random distribution over the allocation timeline; this
// corresponds to a Poisson process with parameter MemProfileRate. In Poisson
// processes, the distance between two samples follows the exponential
// distribution (exp(MemProfileRate)), so the best return value is a random
// number taken from an exponential distribution whose mean is MemProfileRate.
Keith Randall
committed
func nextSample() uintptr {
if MemProfileRate == 1 {
// Callers assign our return value to
// mcache.next_sample, but next_sample is not used
// when the rate is 1. So avoid the math below and
// just return something.
return 0
}
if GOOS == "plan9" {
// Plan 9 doesn't support floating point in note handler.
if g := getg(); g == g.m.gsignal {
return nextSampleNoFP()
}
}
Keith Randall
committed
return uintptr(fastexprand(MemProfileRate))
// fastexprand returns a random number from an exponential distribution with
// the specified mean.
func fastexprand(mean int) int32 {
// Avoid overflow. Maximum possible step is
// -ln(1/(1<<randomBitCount)) * mean, approximately 20 * mean.
case mean > 0x7000000:
mean = 0x7000000
case mean == 0:
// Take a random sample of the exponential distribution exp(-mean*x).
// The probability distribution function is mean*exp(-mean*x), so the CDF is
// p = 1 - exp(-mean*x), so
// q = 1 - p == exp(-mean*x)
// log_e(q) = -mean*x
// -log_e(q)/mean = x
// x = -log_e(q) * mean
// x = log_2(q) * (-log_e(2)) * mean ; Using log_2 for efficiency
q := fastrandn(1<<randomBitCount) + 1
qlog := fastlog2(float64(q)) - randomBitCount
if qlog > 0 {
qlog = 0
}
const minusLog2 = -0.6931471805599453 // -ln(2)
return int32(qlog*(minusLog2*float64(mean))) + 1
// nextSampleNoFP is similar to nextSample, but uses older,
// simpler code to avoid floating point.
Keith Randall
committed
func nextSampleNoFP() uintptr {
// Set first allocation sample size.
rate := MemProfileRate
if rate > 0x3fffffff { // make 2*rate not overflow
rate = 0x3fffffff
}
if rate != 0 {
return uintptr(fastrandn(uint32(2 * rate)))
}
return 0
}
type persistentAlloc struct {
base *notInHeap
off uintptr
var globalAlloc struct {
mutex
persistentAlloc
}
// persistentChunkSize is the number of bytes we allocate when we grow
// a persistentAlloc.
const persistentChunkSize = 256 << 10
// persistentChunks is a list of all the persistent chunks we have
// allocated. The list is maintained through the first word in the
// persistent chunk. This is updated atomically.
var persistentChunks *notInHeap
// Wrapper around sysAlloc that can allocate small chunks.
// There is no associated free operation.
// Intended for things like function/type/debug-related persistent data.
// If align is 0, uses default align (currently 8).
// The returned memory will be zeroed.
//
// Consider marking persistentalloc'd types go:notinheap.
func persistentalloc(size, align uintptr, sysStat *sysMemStat) unsafe.Pointer {
var p *notInHeap
systemstack(func() {
p = persistentalloc1(size, align, sysStat)
})
return unsafe.Pointer(p)
}
// Must run on system stack because stack growth can (re)invoke it.
// See issue 9174.
//go:systemstack
func persistentalloc1(size, align uintptr, sysStat *sysMemStat) *notInHeap {
const (
maxBlock = 64 << 10 // VM reservation granularity is 64K on windows
)
if size == 0 {
throw("persistentalloc: size == 0")
}
if align != 0 {
if align&(align-1) != 0 {
throw("persistentalloc: align is not a power of 2")
}
if align > _PageSize {
throw("persistentalloc: align is too large")
}
} else {
align = 8
}
if size >= maxBlock {
return (*notInHeap)(sysAlloc(size, sysStat))
mp := acquirem()
var persistent *persistentAlloc
if mp != nil && mp.p != 0 {
persistent = &mp.p.ptr().palloc
} else {
lock(&globalAlloc.mutex)
persistent = &globalAlloc.persistentAlloc
}
persistent.off = alignUp(persistent.off, align)
if persistent.off+size > persistentChunkSize || persistent.base == nil {
persistent.base = (*notInHeap)(sysAlloc(persistentChunkSize, &memstats.other_sys))
if persistent.base == nil {
if persistent == &globalAlloc.persistentAlloc {
unlock(&globalAlloc.mutex)
}
throw("runtime: cannot allocate memory")
// Add the new chunk to the persistentChunks list.
for {
chunks := uintptr(unsafe.Pointer(persistentChunks))
*(*uintptr)(unsafe.Pointer(persistent.base)) = chunks
if atomic.Casuintptr((*uintptr)(unsafe.Pointer(&persistentChunks)), chunks, uintptr(unsafe.Pointer(persistent.base))) {
break
}
}
Michael Anthony Knyszek
committed
persistent.off = alignUp(goarch.PtrSize, align)
p := persistent.base.add(persistent.off)
persistent.off += size
releasem(mp)
if persistent == &globalAlloc.persistentAlloc {
unlock(&globalAlloc.mutex)
}
if sysStat != &memstats.other_sys {
sysStat.add(int64(size))
memstats.other_sys.add(-int64(size))
// inPersistentAlloc reports whether p points to memory allocated by
// persistentalloc. This must be nosplit because it is called by the
// cgo checker code, which is called by the write barrier code.
//go:nosplit
func inPersistentAlloc(p uintptr) bool {
chunk := atomic.Loaduintptr((*uintptr)(unsafe.Pointer(&persistentChunks)))
for chunk != 0 {
if p >= chunk && p < chunk+persistentChunkSize {
return true
}
chunk = *(*uintptr)(unsafe.Pointer(chunk))
}
return false
}
// linearAlloc is a simple linear allocator that pre-reserves a region
// of memory and then optionally maps that region into the Ready state
// as needed.
//
// The caller is responsible for locking.
type linearAlloc struct {
next uintptr // next free byte
mapped uintptr // one byte past end of mapped space
end uintptr // end of reserved space
mapMemory bool // transition memory from Reserved to Ready if true
func (l *linearAlloc) init(base, size uintptr, mapMemory bool) {
if base+size < base {
// Chop off the last byte. The runtime isn't prepared
// to deal with situations where the bounds could overflow.
// Leave that memory reserved, though, so we don't map it
// later.
size -= 1
}
l.next, l.mapped = base, base
l.end = base + size
l.mapMemory = mapMemory
func (l *linearAlloc) alloc(size, align uintptr, sysStat *sysMemStat) unsafe.Pointer {
p := alignUp(l.next, align)
if p+size > l.end {
return nil
}
l.next = p + size
if pEnd := alignUp(l.next-1, physPageSize); pEnd > l.mapped {
if l.mapMemory {
// Transition from Reserved to Prepared to Ready.
sysMap(unsafe.Pointer(l.mapped), pEnd-l.mapped, sysStat)
sysUsed(unsafe.Pointer(l.mapped), pEnd-l.mapped)
}
l.mapped = pEnd
}
return unsafe.Pointer(p)
}
// notInHeap is off-heap memory allocated by a lower-level allocator
// like sysAlloc or persistentAlloc.
//
// In general, it's better to use real types marked as go:notinheap,
// but this serves as a generic type for situations where that isn't
// possible (like in the allocators).
//
// TODO: Use this as the return type of sysAlloc, persistentAlloc, etc?
//
//go:notinheap
type notInHeap struct{}
func (p *notInHeap) add(bytes uintptr) *notInHeap {
return (*notInHeap)(unsafe.Pointer(uintptr(unsafe.Pointer(p)) + bytes))
}
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
// computeRZlog computes the size of the redzone.
// Refer to the implementation of the compiler-rt.
func computeRZlog(userSize uintptr) uintptr {
switch {
case userSize <= (64 - 16):
return 16 << 0
case userSize <= (128 - 32):
return 16 << 1
case userSize <= (512 - 64):
return 16 << 2
case userSize <= (4096 - 128):
return 16 << 3
case userSize <= (1<<14)-256:
return 16 << 4
case userSize <= (1<<15)-512:
return 16 << 5
case userSize <= (1<<16)-1024:
return 16 << 6
default:
return 16 << 7
}
}