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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Memory allocator, based on tcmalloc.
// http://goog-perftools.sourceforge.net/doc/tcmalloc.html
// The main allocator works in runs of pages.
// Small allocation sizes (up to and including 32 kB) are
// rounded to one of about 100 size classes, each of which
// has its own free list of objects of exactly that size.
// Any free page of memory can be split into a set of objects
// of one size class, which are then managed using free list
// allocators.
//
// The allocator's data structures are:
//
// FixAlloc: a free-list allocator for fixed-size objects,
// used to manage storage used by the allocator.
// MHeap: the malloc heap, managed at page (4096-byte) granularity.
// MSpan: a run of pages managed by the MHeap.
// MCentral: a shared free list for a given size class.
// MCache: a per-thread (in Go, per-P) cache for small objects.
// MStats: allocation statistics.
//
// Allocating a small object proceeds up a hierarchy of caches:
//
// 1. Round the size up to one of the small size classes
// and look in the corresponding MCache free list.
// If the list is not empty, allocate an object from it.
// This can all be done without acquiring a lock.
//
// 2. If the MCache free list is empty, replenish it by
// taking a bunch of objects from the MCentral free list.
// Moving a bunch amortizes the cost of acquiring the MCentral lock.
//
// 3. If the MCentral free list is empty, replenish it by
// allocating a run of pages from the MHeap and then
// chopping that memory into objects of the given size.
// Allocating many objects amortizes the cost of locking
// the heap.
//
// 4. If the MHeap is empty or has no page runs large enough,
// allocate a new group of pages (at least 1MB) from the
// operating system. Allocating a large run of pages
// amortizes the cost of talking to the operating system.
//
// Freeing a small object proceeds up the same hierarchy:
//
// 1. Look up the size class for the object and add it to
// the MCache free list.
//
// 2. If the MCache free list is too long or the MCache has
// too much memory, return some to the MCentral free lists.
//
// 3. If all the objects in a given span have returned to
// the MCentral list, return that span to the page heap.
//
// 4. If the heap has too much memory, return some to the
// operating system.
//
// TODO(rsc): Step 4 is not implemented.
//
// Allocating and freeing a large object uses the page heap
// directly, bypassing the MCache and MCentral free lists.
//
// The small objects on the MCache and MCentral free lists
// may or may not be zeroed. They are zeroed if and only if
// the second word of the object is zero. A span in the
// page heap is zeroed unless s->needzero is set. When a span
// is allocated to break into small objects, it is zeroed if needed
// and s->needzero is set. There are two main benefits to delaying the
// zeroing this way:
//
// 1. stack frames allocated from the small object lists
// or the page heap can avoid zeroing altogether.
// 2. the cost of zeroing when reusing a small object is
// charged to the mutator, not the garbage collector.
package runtime
import (
"runtime/internal/sys"
"unsafe"
)
const (
debugMalloc = false
flagNoScan = _FlagNoScan
flagNoZero = _FlagNoZero
maxTinySize = _TinySize
tinySizeClass = _TinySizeClass
maxSmallSize = _MaxSmallSize
pageShift = _PageShift
pageSize = _PageSize
pageMask = _PageMask
mSpanInUse = _MSpanInUse
concurrentSweep = _ConcurrentSweep
)
const (
_PageShift = 13
_PageSize = 1 << _PageShift
_PageMask = _PageSize - 1
)
const (
// _64bit = 1 on 64-bit systems, 0 on 32-bit systems
_64bit = 1 << (^uintptr(0) >> 63) / 2
// Computed constant. The definition of MaxSmallSize and the
// algorithm in msize.go produces some number of different allocation
// size classes. NumSizeClasses is that number. It's needed here
// because there are static arrays of this length; when msize runs its
// size choosing algorithm it double-checks that NumSizeClasses agrees.
_NumSizeClasses = 67
// Tunable constants.
_MaxSmallSize = 32 << 10
// Tiny allocator parameters, see "Tiny allocator" comment in malloc.go.
_TinySize = 16
_TinySizeClass = 2
_FixAllocChunk = 16 << 10 // Chunk size for FixAlloc
_MaxMHeapList = 1 << (20 - _PageShift) // Maximum page length for fixed-size list in MHeap.
_HeapAllocChunk = 1 << 20 // Chunk size for heap growth
// Per-P, per order stack segment cache size.
_StackCacheSize = 32 * 1024
// Number of orders that get caching. Order 0 is FixedStack
// and each successive order is twice as large.
// We want to cache 2KB, 4KB, 8KB, and 16KB stacks. Larger stacks
// will be allocated directly.
// Since FixedStack is different on different systems, we
// must vary NumStackOrders to keep the same maximum cached size.
// OS | FixedStack | NumStackOrders
// -----------------+------------+---------------
// linux/darwin/bsd | 2KB | 4
// windows/32 | 4KB | 3
// windows/64 | 8KB | 2
// plan9 | 4KB | 3
_NumStackOrders = 4 - sys.PtrSize/4*sys.GoosWindows - 1*sys.GoosPlan9
// Number of bits in page to span calculations (4k pages).
// On Windows 64-bit we limit the arena to 32GB or 35 bits.
// Windows counts memory used by page table into committed memory
// of the process, so we can't reserve too much memory.
// See https://golang.org/issue/5402 and https://golang.org/issue/5236.
// On other 64-bit platforms, we limit the arena to 512GB, or 39 bits.
// On 32-bit, we don't bother limiting anything, so we use the full 32-bit address.
// On Darwin/arm64, we cannot reserve more than ~5GB of virtual memory,
// but as most devices have less than 4GB of physical memory anyway, we
// try to be conservative here, and only ask for a 2GB heap.
_MHeapMap_TotalBits = (_64bit*sys.GoosWindows)*35 + (_64bit*(1-sys.GoosWindows)*(1-sys.GoosDarwin*sys.GoarchArm64))*39 + sys.GoosDarwin*sys.GoarchArm64*31 + (1-_64bit)*32
_MHeapMap_Bits = _MHeapMap_TotalBits - _PageShift
_MaxMem = uintptr(1<<_MHeapMap_TotalBits - 1)
// Max number of threads to run garbage collection.
// 2, 3, and 4 are all plausible maximums depending
// on the hardware details of the machine. The garbage
// collector scales well to 32 cpus.
_MaxGcproc = 32
)
// Page number (address>>pageShift)
type pageID uintptr
const _MaxArena32 = 2 << 30
// OS-defined helpers:
//
// sysAlloc obtains a large chunk of zeroed memory from the
// operating system, typically on the order of a hundred kilobytes
// or a megabyte.
// NOTE: sysAlloc returns OS-aligned memory, but the heap allocator
// may use larger alignment, so the caller must be careful to realign the
// memory obtained by sysAlloc.
//
// SysUnused notifies the operating system that the contents
// of the memory region are no longer needed and can be reused
// for other purposes.
// SysUsed notifies the operating system that the contents
// of the memory region are needed again.
//
// SysFree returns it unconditionally; this is only used if
// an out-of-memory error has been detected midway through
// an allocation. It is okay if SysFree is a no-op.
//
// SysReserve reserves address space without allocating memory.
// If the pointer passed to it is non-nil, the caller wants the
// reservation there, but SysReserve can still choose another
// location if that one is unavailable. On some systems and in some
// cases SysReserve will simply check that the address space is
// available and not actually reserve it. If SysReserve returns
// non-nil, it sets *reserved to true if the address space is
// reserved, false if it has merely been checked.
// NOTE: SysReserve returns OS-aligned memory, but the heap allocator
// may use larger alignment, so the caller must be careful to realign the
// memory obtained by sysAlloc.
//
// SysMap maps previously reserved address space for use.
// The reserved argument is true if the address space was really
// reserved, not merely checked.
//
// SysFault marks a (already sysAlloc'd) region to fault
// if accessed. Used only for debugging the runtime.
func mallocinit() {
initSizes()
if class_to_size[_TinySizeClass] != _TinySize {
throw("bad TinySizeClass")
}
var p, bitmapSize, spansSize, pSize, limit uintptr
var reserved bool
// limit = runtime.memlimit();
// See https://golang.org/issue/5049
// TODO(rsc): Fix after 1.1.
limit = 0
// Set up the allocation arena, a contiguous area of memory where
// allocated data will be found. The arena begins with a bitmap large
// enough to hold 4 bits per allocated word.
if sys.PtrSize == 8 && (limit == 0 || limit > 1<<30) {
// On a 64-bit machine, allocate from a single contiguous reservation.
// 512 GB (MaxMem) should be big enough for now.
//
// The code will work with the reservation at any address, but ask
// SysReserve to use 0x0000XXc000000000 if possible (XX=00...7f).
// Allocating a 512 GB region takes away 39 bits, and the amd64
// doesn't let us choose the top 17 bits, so that leaves the 9 bits
// in the middle of 0x00c0 for us to choose. Choosing 0x00c0 means
// that the valid memory addresses will begin 0x00c0, 0x00c1, ..., 0x00df.
// In little-endian, that's c0 00, c1 00, ..., df 00. None of those are valid
// UTF-8 sequences, and they are otherwise as far away from
// ff (likely a common byte) as possible. If that fails, we try other 0xXXc0
// addresses. An earlier attempt to use 0x11f8 caused out of memory errors
// on OS X during thread allocations. 0x00c0 causes conflicts with
// AddressSanitizer which reserves all memory up to 0x0100.
// These choices are both for debuggability and to reduce the
// odds of a conservative garbage collector (as is still used in gccgo)
// not collecting memory because some non-pointer block of memory
// had a bit pattern that matched a memory address.
//
// Actually we reserve 544 GB (because the bitmap ends up being 32 GB)
// but it hardly matters: e0 00 is not valid UTF-8 either.
//
// If this fails we fall back to the 32 bit memory mechanism
//
// However, on arm64, we ignore all this advice above and slam the
// allocation at 0x40 << 32 because when using 4k pages with 3-level
// translation buffers, the user address space is limited to 39 bits
// On darwin/arm64, the address space is even smaller.
arenaSize := round(_MaxMem, _PageSize)
bitmapSize = arenaSize / (sys.PtrSize * 8 / 4)
spansSize = arenaSize / _PageSize * sys.PtrSize
spansSize = round(spansSize, _PageSize)
for i := 0; i <= 0x7f; i++ {
switch {
case GOARCH == "arm64" && GOOS == "darwin":
p = uintptr(i)<<40 | uintptrMask&(0x0013<<28)
case GOARCH == "arm64":
p = uintptr(i)<<40 | uintptrMask&(0x0040<<32)
default:
p = uintptr(i)<<40 | uintptrMask&(0x00c0<<32)
}
pSize = bitmapSize + spansSize + arenaSize + _PageSize
p = uintptr(sysReserve(unsafe.Pointer(p), pSize, &reserved))
if p != 0 {
break
}
}
}
if p == 0 {
// On a 32-bit machine, we can't typically get away
// with a giant virtual address space reservation.
// Instead we map the memory information bitmap
// immediately after the data segment, large enough
// to handle another 2GB of mappings (256 MB),
// along with a reservation for an initial arena.
// When that gets used up, we'll start asking the kernel
// for any memory anywhere and hope it's in the 2GB
// following the bitmap (presumably the executable begins
// near the bottom of memory, so we'll have to use up
// most of memory before the kernel resorts to giving out
// memory before the beginning of the text segment).
//
// Alternatively we could reserve 512 MB bitmap, enough
// for 4GB of mappings, and then accept any memory the
// kernel threw at us, but normally that's a waste of 512 MB
// of address space, which is probably too much in a 32-bit world.
// If we fail to allocate, try again with a smaller arena.
// This is necessary on Android L where we share a process
// with ART, which reserves virtual memory aggressively.
arenaSizes := []uintptr{
512 << 20,
256 << 20,
128 << 20,
}
for _, arenaSize := range arenaSizes {
bitmapSize = _MaxArena32 / (sys.PtrSize * 8 / 4)
spansSize = _MaxArena32 / _PageSize * sys.PtrSize
if limit > 0 && arenaSize+bitmapSize+spansSize > limit {
bitmapSize = (limit / 9) &^ ((1 << _PageShift) - 1)
arenaSize = bitmapSize * 8
spansSize = arenaSize / _PageSize * sys.PtrSize
}
spansSize = round(spansSize, _PageSize)
// SysReserve treats the address we ask for, end, as a hint,
// not as an absolute requirement. If we ask for the end
// of the data segment but the operating system requires
// a little more space before we can start allocating, it will
// give out a slightly higher pointer. Except QEMU, which
// is buggy, as usual: it won't adjust the pointer upward.
// So adjust it upward a little bit ourselves: 1/4 MB to get
// away from the running binary image and then round up
// to a MB boundary.
p = round(firstmoduledata.end+(1<<18), 1<<20)
pSize = bitmapSize + spansSize + arenaSize + _PageSize
p = uintptr(sysReserve(unsafe.Pointer(p), pSize, &reserved))
if p != 0 {
break
}
}
if p == 0 {
throw("runtime: cannot reserve arena virtual address space")
}
}
// PageSize can be larger than OS definition of page size,
// so SysReserve can give us a PageSize-unaligned pointer.
// To overcome this we ask for PageSize more and round up the pointer.
p1 := round(p, _PageSize)
mheap_.spans = (**mspan)(unsafe.Pointer(p1))
mheap_.bitmap = p1 + spansSize
mheap_.arena_start = p1 + (spansSize + bitmapSize)
mheap_.arena_used = mheap_.arena_start
mheap_.arena_end = p + pSize
mheap_.arena_reserved = reserved
if mheap_.arena_start&(_PageSize-1) != 0 {
println("bad pagesize", hex(p), hex(p1), hex(spansSize), hex(bitmapSize), hex(_PageSize), "start", hex(mheap_.arena_start))
throw("misrounded allocation in mallocinit")
}
// Initialize the rest of the allocator.
mheap_.init(spansSize)
_g_ := getg()
_g_.m.mcache = allocmcache()
}
// sysReserveHigh reserves space somewhere high in the address space.
// sysReserve doesn't actually reserve the full amount requested on
// 64-bit systems, because of problems with ulimit. Instead it checks
// that it can get the first 64 kB and assumes it can grab the rest as
// needed. This doesn't work well with the "let the kernel pick an address"
// mode, so don't do that. Pick a high address instead.
func sysReserveHigh(n uintptr, reserved *bool) unsafe.Pointer {
if sys.PtrSize == 4 {
return sysReserve(nil, n, reserved)
}
for i := 0; i <= 0x7f; i++ {
p := uintptr(i)<<40 | uintptrMask&(0x00c0<<32)
*reserved = false
p = uintptr(sysReserve(unsafe.Pointer(p), n, reserved))
if p != 0 {
return unsafe.Pointer(p)
}
}
return sysReserve(nil, n, reserved)
}
func (h *mheap) sysAlloc(n uintptr) unsafe.Pointer {
if n > h.arena_end-h.arena_used {
// We are in 32-bit mode, maybe we didn't use all possible address space yet.
// Reserve some more space.
p_size := round(n+_PageSize, 256<<20)
new_end := h.arena_end + p_size // Careful: can overflow
if h.arena_end <= new_end && new_end <= h.arena_start+_MaxArena32 {
// TODO: It would be bad if part of the arena
// is reserved and part is not.
var reserved bool
p := uintptr(sysReserve(unsafe.Pointer(h.arena_end), p_size, &reserved))
if p == 0 {
return nil
}
if p == h.arena_end {
h.arena_end = new_end
h.arena_reserved = reserved
} else if h.arena_start <= p && p+p_size <= h.arena_start+_MaxArena32 {
// Keep everything page-aligned.
// Our pages are bigger than hardware pages.
h.arena_end = p + p_size
used := p + (-p & (_PageSize - 1))
h.mapBits(used)
h.mapSpans(used)
h.arena_used = used
h.arena_reserved = reserved
} else {
// We haven't added this allocation to
// the stats, so subtract it from a
// fake stat (but avoid underflow).
stat := uint64(p_size)
sysFree(unsafe.Pointer(p), p_size, &stat)
}
}
}
if n <= h.arena_end-h.arena_used {
// Keep taking from our reservation.
p := h.arena_used
sysMap(unsafe.Pointer(p), n, h.arena_reserved, &memstats.heap_sys)
h.mapBits(p + n)
h.mapSpans(p + n)
h.arena_used = p + n
if raceenabled {
racemapshadow(unsafe.Pointer(p), n)
}
if p&(_PageSize-1) != 0 {
throw("misrounded allocation in MHeap_SysAlloc")
}
return unsafe.Pointer(p)
}
// If using 64-bit, our reservation is all we have.
if h.arena_end-h.arena_start >= _MaxArena32 {
return nil
}
// On 32-bit, once the reservation is gone we can
// try to get memory at a location chosen by the OS
// and hope that it is in the range we allocated bitmap for.
p_size := round(n, _PageSize) + _PageSize
p := uintptr(sysAlloc(p_size, &memstats.heap_sys))
if p == 0 {
return nil
}
if p < h.arena_start || p+p_size-h.arena_start >= _MaxArena32 {
top := ^uintptr(0)
if top-h.arena_start > _MaxArena32 {
top = h.arena_start + _MaxArena32
}
print("runtime: memory allocated by OS (", hex(p), ") not in usable range [", hex(h.arena_start), ",", hex(top), ")\n")
sysFree(unsafe.Pointer(p), p_size, &memstats.heap_sys)
return nil
}
p_end := p + p_size
p += -p & (_PageSize - 1)
if p+n > h.arena_used {
h.mapBits(p + n)
h.mapSpans(p + n)
h.arena_used = p + n
if p_end > h.arena_end {
h.arena_end = p_end
}
if raceenabled {
racemapshadow(unsafe.Pointer(p), n)
}
}
if p&(_PageSize-1) != 0 {
throw("misrounded allocation in MHeap_SysAlloc")
}
return unsafe.Pointer(p)
}
// base address for all 0-byte allocations
var zerobase uintptr
const (
// flags to malloc
_FlagNoScan = 1 << 0 // GC doesn't have to scan object
_FlagNoZero = 1 << 1 // don't zero memory
)
// Allocate an object of size bytes.
// Small objects are allocated from the per-P cache's free lists.
// Large objects (> 32 kB) are allocated straight from the heap.
func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
if gcphase == _GCmarktermination {
throw("mallocgc called with gcphase == _GCmarktermination")
}
if size == 0 {
return unsafe.Pointer(&zerobase)
}
if flags&flagNoScan == 0 && typ == nil {
throw("malloc missing type")
}
if debug.sbrk != 0 {
align := uintptr(16)
if typ != nil {
align = uintptr(typ.align)
}
return persistentalloc(size, align, &memstats.other_sys)
}
// assistG is the G to charge for this allocation, or nil if
// GC is not currently active.
var assistG *g
if gcBlackenEnabled != 0 {
// Charge the current user G for this allocation.
assistG = getg()
if assistG.m.curg != nil {
assistG = assistG.m.curg
}
// Charge the allocation against the G. We'll account
// for internal fragmentation at the end of mallocgc.
assistG.gcAssistBytes -= int64(size)
if assistG.gcAssistBytes < 0 {
// This G is in debt. Assist the GC to correct
// this before allocating. This must happen
// before disabling preemption.
gcAssistAlloc(assistG)
}
}
// Set mp.mallocing to keep from being preempted by GC.
mp := acquirem()
if mp.mallocing != 0 {
throw("malloc deadlock")
}
if mp.gsignal == getg() {
throw("malloc during signal")
}
mp.mallocing = 1
shouldhelpgc := false
dataSize := size
c := gomcache()
var s *mspan
var x unsafe.Pointer
if size <= maxSmallSize {
if flags&flagNoScan != 0 && size < maxTinySize {
// Tiny allocator.
//
// Tiny allocator combines several tiny allocation requests
// into a single memory block. The resulting memory block
// is freed when all subobjects are unreachable. The subobjects
// must be FlagNoScan (don't have pointers), this ensures that
// 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 = round(off, 8)
} else if size&3 == 0 {
off = round(off, 4)
} else if size&1 == 0 {
off = round(off, 2)
}
if off+size <= maxTinySize && c.tiny != 0 {
// The object fits into existing tiny block.
x = unsafe.Pointer(c.tiny + off)
c.tinyoffset = off + size
c.local_tinyallocs++
mp.mallocing = 0
releasem(mp)
return x
}
// Allocate a new maxTinySize block.
s = c.alloc[tinySizeClass]
v := s.freelist
if v.ptr() == nil {
systemstack(func() {
c.refill(tinySizeClass)
})
shouldhelpgc = true
s = c.alloc[tinySizeClass]
v = s.freelist
}
s.freelist = v.ptr().next
s.ref++
// prefetchnta offers best performance, see change list message.
prefetchnta(uintptr(v.ptr().next))
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 size < c.tinyoffset || c.tiny == 0 {
c.tiny = uintptr(x)
c.tinyoffset = size
}
size = maxTinySize
} else {
var sizeclass int8
if size <= 1024-8 {
sizeclass = size_to_class8[(size+7)>>3]
} else {
sizeclass = size_to_class128[(size-1024+127)>>7]
}
size = uintptr(class_to_size[sizeclass])
s = c.alloc[sizeclass]
v := s.freelist
if v.ptr() == nil {
systemstack(func() {
c.refill(int32(sizeclass))
})
shouldhelpgc = true
s = c.alloc[sizeclass]
v = s.freelist
}
s.freelist = v.ptr().next
s.ref++
// prefetchnta offers best performance, see change list message.
prefetchnta(uintptr(v.ptr().next))
x = unsafe.Pointer(v)
if flags&flagNoZero == 0 {
v.ptr().next = 0
if size > 2*sys.PtrSize && ((*[2]uintptr)(x))[1] != 0 {
memclr(unsafe.Pointer(v), size)
}
}
}
} else {
var s *mspan
shouldhelpgc = true
systemstack(func() {
s = largeAlloc(size, flags)
})
x = unsafe.Pointer(uintptr(s.start << pageShift))
size = s.elemsize
}
if flags&flagNoScan != 0 {
// All objects are pre-marked as noscan. Nothing to do.
} else {
// If allocating a defer+arg block, now that we've picked a malloc size
// large enough to hold everything, cut the "asked for" size down to
// just the defer header, so that the GC bitmap will record the arg block
// as containing nothing at all (as if it were unused space at the end of
// a malloc block caused by size rounding).
// The defer arg areas are scanned as part of scanstack.
if typ == deferType {
dataSize = unsafe.Sizeof(_defer{})
}
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 {
c.local_scan += dataSize - typ.size + typ.ptrdata
}
} else {
c.local_scan += typ.ptrdata
}
// 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()
}
// GCmarkterminate allocates black
// 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.
if gcphase == _GCmarktermination || gcBlackenPromptly {
systemstack(func() {
gcmarknewobject_m(uintptr(x), size)
})
}
if raceenabled {
racemalloc(x, size)
}
if msanenabled {
msanmalloc(x, size)
}
mp.mallocing = 0
releasem(mp)
if debug.allocfreetrace != 0 {
tracealloc(x, size, typ)
}
if rate := MemProfileRate; rate > 0 {
if size < uintptr(rate) && int32(size) < c.next_sample {
c.next_sample -= int32(size)
} else {
mp := acquirem()
profilealloc(mp, x, size)
releasem(mp)
}
}
if assistG != nil {
// Account for internal fragmentation in the assist
// debt now that we know it.
assistG.gcAssistBytes -= int64(size - dataSize)
}
if shouldhelpgc && gcShouldStart(false) {
gcStart(gcBackgroundMode, false)
}
return x
}
func largeAlloc(size uintptr, flag uint32) *mspan {
// print("largeAlloc size=", size, "\n")
if size+_PageSize < size {
throw("out of memory")
}
npages := size >> _PageShift
if size&_PageMask != 0 {
npages++
}
// Deduct credit for this span allocation and sweep if
// necessary. mHeap_Alloc will also sweep npages, so this only
// pays the debt down to npage pages.
deductSweepCredit(npages*_PageSize, npages)
s := mheap_.alloc(npages, 0, true, flag&_FlagNoZero == 0)
if s == nil {
throw("out of memory")
}
s.limit = uintptr(s.start)<<_PageShift + size
heapBitsForSpan(s.base()).initSpan(s.layout())
return s
}
// implementation of new builtin
func newobject(typ *_type) unsafe.Pointer {
flags := uint32(0)
if typ.kind&kindNoPointers != 0 {
flags |= flagNoScan
}
return mallocgc(typ.size, typ, flags)
}
//go:linkname reflect_unsafe_New reflect.unsafe_New
func reflect_unsafe_New(typ *_type) unsafe.Pointer {
return newobject(typ)
}
// implementation of make builtin for slices
func newarray(typ *_type, n uintptr) unsafe.Pointer {
flags := uint32(0)
if typ.kind&kindNoPointers != 0 {
flags |= flagNoScan
}
if int(n) < 0 || (typ.size > 0 && n > _MaxMem/typ.size) {
panic("runtime: allocation size out of range")
}
return mallocgc(typ.size*n, typ, flags)
}
//go:linkname reflect_unsafe_NewArray reflect.unsafe_NewArray
func reflect_unsafe_NewArray(typ *_type, n uintptr) unsafe.Pointer {
return newarray(typ, n)
}
// rawmem returns a chunk of pointerless memory. It is
// not zeroed.
func rawmem(size uintptr) unsafe.Pointer {
return mallocgc(size, nil, flagNoScan|flagNoZero)
}
func profilealloc(mp *m, x unsafe.Pointer, size uintptr) {
mp.mcache.next_sample = nextSample()
mProf_Malloc(x, size)
}
// nextSample returns the next sampling point for heap profiling.
// It produces a random variable with a geometric distribution and
// mean MemProfileRate. This is done by generating a uniformly
// distributed random number and applying the cumulative distribution
// function for an exponential.
func nextSample() int32 {
if GOOS == "plan9" {
// Plan 9 doesn't support floating point in note handler.
if g := getg(); g == g.m.gsignal {
return nextSampleNoFP()
}
}
period := MemProfileRate
// make nextSample not overflow. Maximum possible step is
// -ln(1/(1<<kRandomBitCount)) * period, approximately 20 * period.
switch {
case period > 0x7000000:
period = 0x7000000
case period == 0:
return 0
}
// Let m be the sample rate,
// the probability distribution function is m*exp(-mx), so the CDF is
// p = 1 - exp(-mx), so
// q = 1 - p == exp(-mx)
// log_e(q) = -mx
// -log_e(q)/m = x
// x = -log_e(q) * period
// x = log_2(q) * (-log_e(2)) * period ; Using log_2 for efficiency
const randomBitCount = 26
q := fastrand1()%(1<<randomBitCount) + 1
qlog := fastlog2(float64(q)) - randomBitCount
if qlog > 0 {
qlog = 0
}
const minusLog2 = -0.6931471805599453 // -ln(2)
return int32(qlog*(minusLog2*float64(period))) + 1
}
// nextSampleNoFP is similar to nextSample, but uses older,
// simpler code to avoid floating point.
func nextSampleNoFP() int32 {
// Set first allocation sample size.
rate := MemProfileRate
if rate > 0x3fffffff { // make 2*rate not overflow
rate = 0x3fffffff
}
if rate != 0 {
return int32(int(fastrand1()) % (2 * rate))
}
return 0
}
type persistentAlloc struct {
base unsafe.Pointer
off uintptr
}
var globalAlloc struct {
mutex
persistentAlloc
}
// 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).
func persistentalloc(size, align uintptr, sysStat *uint64) unsafe.Pointer {
var p unsafe.Pointer
systemstack(func() {
p = persistentalloc1(size, align, sysStat)
})
return p
}
// Must run on system stack because stack growth can (re)invoke it.
// See issue 9174.
//go:systemstack
func persistentalloc1(size, align uintptr, sysStat *uint64) unsafe.Pointer {
const (
chunk = 256 << 10
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 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 = round(persistent.off, align)
if persistent.off+size > chunk || persistent.base == nil {
persistent.base = sysAlloc(chunk, &memstats.other_sys)
if persistent.base == nil {
if persistent == &globalAlloc.persistentAlloc {
unlock(&globalAlloc.mutex)
}
throw("runtime: cannot allocate memory")
}
persistent.off = 0
}
p := add(persistent.base, persistent.off)
persistent.off += size
releasem(mp)
if persistent == &globalAlloc.persistentAlloc {
unlock(&globalAlloc.mutex)
}
if sysStat != &memstats.other_sys {
mSysStatInc(sysStat, size)
mSysStatDec(&memstats.other_sys, size)
}
return p
}