golang malloc 代码
文件路径：/src/runtime/malloc.go
/ 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.
/
/ This was originally based on tcmalloc, but has diverged quite a bit.
/ 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 70 size classes, each of which
/ has its own free set 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 a free bitmap.
/
/ The allocator's data structures are:
/
/ fixalloc: a free-list allocator for fixed-size off-heap objects,
/ used to manage storage used by the allocator.
/ mheap: the malloc heap, managed at page (8192-byte) granularity.
/ mspan: a run of in-use pages managed by the mheap.
/ mcentral: collects all spans of a given size class.
/ mcache: a per-P cache of mspans with free space.
/ 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 mspan in this P's mcache.
/ Scan the mspan's free bitmap to find a free slot.
/ If there is a free slot, allocate it.
/ This can all be done without acquiring a lock.
/
/ 2. If the mspan has no free slots, obtain a new mspan
/ from the mcentral's list of mspans of the required size
/ class that have free space.
/ Obtaining a whole span amortizes the cost of locking
/ the mcentral.
/
/ 3. If the mcentral's mspan list is empty, obtain a run
/ of pages from the mheap to use for the mspan.
/
/ 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.
/
/ Sweeping an mspan and freeing objects on it proceeds up a similar
/ hierarchy:
/
/ 1. If the mspan is being swept in response to allocation, it
/ is returned to the mcache to satisfy the allocation.
/
/ 2. Otherwise, if the mspan still has allocated objects in it,
/ it is placed on the mcentral free list for the mspan's size
/ class.
/
/ 3. Otherwise, if all objects in the mspan are free, the mspan's
/ pages are returned to the mheap and the mspan is now dead.
/
/ Allocating and freeing a large object uses the mheap
/ directly, bypassing the mcache and mcentral.
/
/ If mspan.needzero is false, then free object slots in the mspan are
/ already zeroed. Otherwise if needzero is true, objects are zeroed as
/ they are allocated. There are various benefits to delaying zeroing
/ this way:
/
/ 1. Stack frame allocation can avoid zeroing altogether.
/
/ 2. It exhibits better temporal locality, since the program is
/ probably about to write to the memory.
/
/ 3. We don't zero pages that never get reused.
/ Virtual memory layout
/
/ The heap consists of a set of arenas, which are 64MB on 64-bit and
/ 4MB on 32-bit (heapArenaBytes). Each arena's start address is also
/ aligned to the arena size.
/
/ Each arena has an associated heapArena object that stores the
/ metadata for that arena: the heap bitmap for all words in the arena
/ and the span map for all pages in the arena. heapArena objects are
/ themselves allocated off-heap.
/
/ Since arenas are aligned, the address space can be viewed as a
/ series of arena frames. The arena map (mheap_.arenas) maps from
/ arena frame number to *heapArena, or nil for parts of the address
/ space not backed by the Go heap. The arena map is structured as a
/ two-level array consisting of a "L1" arena map and many "L2" arena
/ maps; however, since arenas are large, on many architectures, the
/ arena map consists of a single, large L2 map.
/
/ The arena map covers the entire possible address space, allowing
/ the Go heap to use any part of the address space. The allocator
/ attempts to keep arenas contiguous so that large spans (and hence
/ large objects) can cross arenas.
package runtime
import (
"internal/goarch"
"internal/goos"
"runtime/internal/atomic"
"runtime/internal/math"
"runtime/internal/sys"
"unsafe"
)
const (
maxTinySize = _TinySize
tinySizeClass = _TinySizeClass
maxSmallSize = _MaxSmallSize
pageShift = _PageShift
pageSize = _PageSize
concurrentSweep = _ConcurrentSweep
_PageSize = 1 << _PageShift
_PageMask = _PageSize - 1
/ _64bit = 1 on 64-bit systems, 0 on 32-bit systems
_64bit = 1 << (^uintptr(0) >> 63) / 2
/ Tiny allocator parameters, see "Tiny allocator" comment in malloc.go.
_TinySize = 16
_TinySizeClass = int8(2)
_FixAllocChunk = 16 << 10 / Chunk size for FixAlloc
/ 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 - goarch.PtrSize/4*goos.IsWindows - 1*goos.IsPlan9
/ heapAddrBits is the number of bits in a heap address. On
/ amd64, addresses are sign-extended beyond heapAddrBits. On
/ other arches, they are zero-extended.
/
/ On most 64-bit platforms, we limit this to 48 bits based on a
/ combination of hardware and OS limitations.
/
/ amd64 hardware limits addresses to 48 bits, sign-extended
/ to 64 bits. Addresses where the top 16 bits are not either
/ all 0 or all 1 are "non-canonical" and invalid. Because of
/ these "negative" addresses, we offset addresses by 1<<47
/ (arenaBaseOffset) on amd64 before computing indexes into
/ the heap arenas index. In 2017, amd64 hardware added
/ support for 57 bit addresses; however, currently only Linux
/ supports this extension and the kernel will never choose an
/ address above 1<<47 unless mmap is called with a hint
/ address above 1<<47 (which we never do).
/
/ arm64 hardware (as of ARMv8) limits user addresses to 48
/ bits, in the range [0, 1<<48).
/
/ ppc64, mips64, and s390x support arbitrary 64 bit addresses
/ in hardware. On Linux, Go leans on stricter OS limits. Based
/ on Linux's processor.h, the user address space is limited as
/ follows on 64-bit architectures:
/
/ Architecture Name Maximum Value (exclusive)
/ ---------------------------------------------------------------------
/ amd64 TASK_SIZE_MAX 0x007ffffffff000 (47 bit addresses)
/ arm64 TASK_SIZE_64 0x01000000000000 (48 bit addresses)
/ ppc64{,le} TASK_SIZE_USER64 0x00400000000000 (46 bit addresses)
/ mips64{,le} TASK_SIZE64 0x00010000000000 (40 bit addresses)
/ s390x TASK_SIZE 1<<64 (64 bit addresses)
/
/ These limits may increase over time, but are currently at
/ most 48 bits except on s390x. On all architectures, Linux
/ starts placing mmap'd regions at addresses that are
/ significantly below 48 bits, so even if it's possible to
/ exceed Go's 48 bit limit, it's extremely unlikely in
/ practice.
/
/ On 32-bit platforms, we accept the full 32-bit address
/ space because doing so is cheap.
/ mips32 only has access to the low 2GB of virtual memory, so
/ we further limit it to 31 bits.
/
/ On ios/arm64, although 64-bit pointers are presumably
/ available, pointers are truncated to 33 bits in iOS <14.
/ Furthermore, only the top 4 GiB of the address space are
/ actually available to the application. In iOS >=14, more
/ of the address space is available, and the OS can now
/ provide addresses outside of those 33 bits. Pick 40 bits
/ as a reasonable balance between address space usage by the
/ page allocator, and flexibility for what mmap'd regions
/ we'll accept for the heap. We can't just move to the full
/ 48 bits because this uses too much address space for older
/ iOS versions.
/ TODO(mknyszek): Once iOS <14 is deprecated, promote ios/arm64
/ to a 48-bit address space like every other arm64 platform.
/
/ WebAssembly currently has a limit of 4GB linear memory.
heapAddrBits = (_64bit*(1-goarch.IsWasm)*(1-goos.IsIos*goarch.IsArm64))*48 + (1-_64bit+goarch.IsWasm)*(32-(goarch.IsMips+goarch.IsMipsle)) + 40*goos.IsIos*goarch.IsArm64
/ maxAlloc is the maximum size of an allocation. On 64-bit,
/ it's theoretically possible to allocate 1<<heapAddrBits bytes. On
/ 32-bit, however, this is one less than 1<<32 because the
/ number of bytes in the address space doesn't actually fit
/ in a uintptr.
maxAlloc = (1 << heapAddrBits) - (1-_64bit)*1
/ The number of bits in a heap address, the size of heap
/ arenas, and the L1 and L2 arena map sizes are related by
/
/ (1 << addr bits) = arena size * L1 entries * L2 entries
/
/ Currently, we balance these as follows:
/
/ Platform Addr bits Arena size L1 entries L2 entries
/ -------------- --------- ---------- ---------- -----------
/ */64-bit 48 64MB 1 4M (32MB)
/ windows/64-bit 48 4MB 64 1M (8MB)
/ ios/arm64 33 4MB 1 2048 (8KB)
/ */32-bit 32 4MB 1 1024 (4KB)
/ */mips(le) 31 4MB 1 512 (2KB)
/ heapArenaBytes is the size of a heap arena. The heap
/ consists of mappings of size heapArenaBytes, aligned to
/ heapArenaBytes. The initial heap mapping is one arena.
/
/ This is currently 64MB on 64-bit non-Windows and 4MB on
/ 32-bit and on Windows. We use smaller arenas on Windows
/ because all committed memory is charged to the process,
/ even if it's not touched. Hence, for processes with small
/ heaps, the mapped arena space needs to be commensurate.
/ This is particularly important with the race detector,
/ since it significantly amplifies the cost of committed
/ memory.
heapArenaBytes = 1 << logHeapArenaBytes
/ logHeapArenaBytes is log_2 of heapArenaBytes. For clarity,
/ prefer using heapArenaBytes where possible (we need the
/ constant to compute some other constants).
logHeapArenaBytes = (6+20)*(_64bit*(1-goos.IsWindows)*(1-goarch.IsWasm)*(1-goos.IsIos*goarch.IsArm64)) + (2+20)*(_64bit*goos.IsWindows) + (2+20)*(1-_64bit) + (2+20)*goarch.IsWasm + (2+20)*goos.IsIos*goarch.IsArm64
/ heapArenaBitmapBytes is the size of each heap arena's bitmap.
heapArenaBitmapBytes = heapArenaBytes / (goarch.PtrSize * 8 / 2)
pagesPerArena = heapArenaBytes / pageSize
/ arenaL1Bits is the number of bits of the arena number
/ covered by the first level arena map.
/
/ This number should be small, since the first level arena
/ map requires PtrSize*(1<<arenaL1Bits) of space in the
/ binary's BSS. It can be zero, in which case the first level
/ index is effectively unused. There is a performance benefit
/ to this, since the generated code can be more efficient,
/ but comes at the cost of having a large L2 mapping.
/
/ We use the L1 map on 64-bit Windows because the arena size
/ is small, but the address space is still 48 bits, and
/ there's a high cost to having a large L2.
arenaL1Bits = 6 * (_64bit * goos.IsWindows)
/ arenaL2Bits is the number of bits of the arena number
/ covered by the second level arena index.
/
/ The size of each arena map allocation is proportional to
/ 1<<arenaL2Bits, so it's important that this not be too
/ large. 48 bits leads to 32MB arena index allocations, which
/ is about the practical threshold.
arenaL2Bits = heapAddrBits - logHeapArenaBytes - arenaL1Bits
/ arenaL1Shift is the number of bits to shift an arena frame
/ number by to compute an index into the first level arena map.
arenaL1Shift = arenaL2Bits
/ arenaBits is the total bits in a combined arena map index.
/ This is split between the index into the L1 arena map and
/ the L2 arena map.
arenaBits = arenaL1Bits + arenaL2Bits
/ arenaBaseOffset is the pointer value that corresponds to
/ index 0 in the heap arena map.
/
/ On amd64, the address space is 48 bits, sign extended to 64
/ bits. This offset lets us handle "negative" addresses (or
/ high addresses if viewed as unsigned).
/
/ On aix/ppc64, this offset allows to keep the heapAddrBits to
/ 48. Otherwise, it would be 60 in order to handle mmap addresses
/ (in range 0x0a00000000000000 - 0x0afffffffffffff). But in this
/ case, the memory reserved in (s *pageAlloc).init for chunks
/ is causing important slowdowns.
/
/ On other platforms, the user address space is contiguous
/ and starts at 0, so no offset is necessary.
arenaBaseOffset = 0xffff800000000000*goarch.IsAmd64 + 0x0a00000000000000*goos.IsAix
/ A typed version of this constant that will make it into DWARF (for viewcore).
arenaBaseOffsetUintptr = uintptr(arenaBaseOffset)
/ 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
/ minLegalPointer is the smallest possible legal pointer.
/ This is the smallest possible architectural page size,
/ since we assume that the first page is never mapped.
/
/ This should agree with minZeroPage in the compiler.
minLegalPointer uintptr = 4096
)
/ physPageSize is the size in bytes of the OS's physical pages.
/ Mapping and unmapping operations must be done at multiples of
/ physPageSize.
/
/ This must be set by the OS init code (typically in osinit) before
/ mallocinit.
var physPageSize uintptr
/ physHugePageSize is the size in bytes of the OS's default physical huge
/ page size whose allocation is opaque to the application. It is assumed
/ and verified to be a power of two.
/
/ If set, this must be set by the OS init code (typically in osinit) before
/ mallocinit. However, setting it at all is optional, and leaving the default
/ value is always safe (though potentially less efficient).
/
/ Since physHugePageSize is always assumed to be a power of two,
/ physHugePageShift is defined as physHugePageSize == 1 << physHugePageShift.
/ The purpose of physHugePageShift is to avoid doing divisions in
/ performance critical functions.
var (
physHugePageSize uintptr
physHugePageShift uint
)
func mallocinit() {
if class_to_size[_TinySizeClass] != _TinySize {
throw("bad TinySizeClass")
}
if heapArenaBitmapBytes&(heapArenaBitmapBytes-1) != 0 {
/ heapBits expects modular arithmetic on bitmap
/ addresses to work.
throw("heapArenaBitmapBytes not a power of 2")
}
/ Check physPageSize.
if physPageSize == 0 {
/ The OS init code failed to fetch the physical page size.
throw("failed to get system page size")
}
if physPageSize > maxPhysPageSize {
print("system page size (", physPageSize, ") is larger than maximum page size (", maxPhysPageSize, ")\n")
throw("bad system page size")
}
if physPageSize < minPhysPageSize {
print("system page size (", physPageSize, ") is smaller than minimum page size (", minPhysPageSize, ")\n")
throw("bad system page size")
}
if physPageSize&(physPageSize-1) != 0 {
print("system page size (", physPageSize, ") must be a power of 2\n")
throw("bad system page size")
}
if physHugePageSize&(physHugePageSize-1) != 0 {
print("system huge page size (", physHugePageSize, ") must be a power of 2\n")
throw("bad system huge page size")
}
if physHugePageSize > maxPhysHugePageSize {
/ physHugePageSize is greater than the maximum supported huge page size.
/ Don't throw here, like in the other cases, since a system configured
/ in this way isn't wrong, we just don't have the code to support them.
/ Instead, silently set the huge page size to zero.
physHugePageSize = 0
}
if physHugePageSize != 0 {
/ Since physHugePageSize is a power of 2, it suffices to increase
/ physHugePageShift until 1<<physHugePageShift == physHugePageSize.
for 1<<physHugePageShift != physHugePageSize {
physHugePageShift++
}
}
if pagesPerArena%pagesPerSpanRoot != 0 {
print("pagesPerArena (", pagesPerArena, ") is not divisible by pagesPerSpanRoot (", pagesPerSpanRoot, ")\n")
throw("bad pagesPerSpanRoot")
}
if pagesPerArena%pagesPerReclaimerChunk != 0 {
print("pagesPerArena (", pagesPerArena, ") is not divisible by pagesPerReclaimerChunk (", pagesPerReclaimerChunk, ")\n")
throw("bad pagesPerReclaimerChunk")
}
/ Initialize the heap.
mheap_.init()
mcache0 = allocmcache()
lockInit(&gcBitsArenas.lock, lockRankGcBitsArenas)
lockInit(&profInsertLock, lockRankProfInsert)
lockInit(&profBlockLock, lockRankProfBlock)
lockInit(&profMemActiveLock, lockRankProfMemActive)
for i := range profMemFutureLock {
lockInit(&profMemFutureLock[i], lockRankProfMemFuture)
}
lockInit(&globalAlloc.mutex, lockRankGlobalAlloc)
/ Create initial arena growth hints.
if goarch.PtrSize == 8 {
/ On a 64-bit machine, we pick the following hints
/ because:
/
/ 1. Starting from the middle of the address space
/ makes it easier to grow out a contiguous range
/ without running in to some other mapping.
/
/ 2. This makes Go heap addresses more easily
/ recognizable when debugging.
/
/ 3. Stack scanning in gccgo is still conservative,
/ so it's important that addresses be distinguishable
/ from other data.
/
/ Starting at 0x00c0 means that the valid memory addresses
/ will begin 0x00c0, 0x00c1, ...
/ In little-endian, that's c0 00, c1 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 reduce the odds of a conservative garbage collector
/ not collecting memory because some non-pointer block of memory
/ had a bit pattern that matched a memory address.
/
/ 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 ios/arm64, the address space is even smaller.
/
/ On AIX, mmaps starts at 0x0A00000000000000 for 64-bit.
/ processes.
for i := 0x7f; i >= 0; i-- {
var p uintptr
switch {
case raceenabled:
/ The TSAN runtime requires the heap
/ to be in the range [0x00c000000000,
/ 0x00e000000000).
p = uintptr(i)<<32 | uintptrMask&(0x00c0<<32)
if p >= uintptrMask&0x00e000000000 {
continue
}
case GOARCH == "arm64" && GOOS == "ios":
p = uintptr(i)<<40 | uintptrMask&(0x0013<<28)
case GOARCH == "arm64":
p = uintptr(i)<<40 | uintptrMask&(0x0040<<32)
case GOOS == "aix":
if i == 0 {
/ We don't use addresses directly after 0x0A00000000000000
/ to avoid collisions with others mmaps done by non-go programs.
continue
}
p = uintptr(i)<<40 | uintptrMask&(0xa0<<52)
default:
p = uintptr(i)<<40 | uintptrMask&(0x00c0<<32)
}
hint := (*arenaHint)(mheap_.arenaHintAlloc.alloc())
hint.addr = p
hint.next, mheap_.arenaHints = mheap_.arenaHints, hint
}
} else {
/ On a 32-bit machine, we're much more concerned
/ about keeping the usable heap contiguous.
/ Hence:
/
/ 1. We reserve space for all heapArenas up front so
/ they don't get interleaved with the heap. They're
/ ~258MB, so this isn't too bad. (We could reserve a
/ smaller amount of space up front if this is a
/ problem.)
/
/ 2. We hint the heap to start right above the end of
/ the binary so we have the best chance of keeping it
/ contiguous.
/
/ 3. We try to stake out a reasonably large initial
/ heap reservation.
const arenaMetaSize = (1 << arenaBits) * unsafe.Sizeof(heapArena{})
meta := uintptr(sysReserve(nil, arenaMetaSize))
if meta != 0 {
mheap_.heapArenaAlloc.init(meta, arenaMetaSize, true)
}
/ We want to start the arena low, but if we're linked
/ against C code, it's possible global constructors
/ have called malloc and adjusted the process' brk.
/ Query the brk so we can avoid trying to map the
/ region over it (which will cause the kernel to put
/ the region somewhere else, likely at a high
/ address).
procBrk := sbrk0()
/ 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.
p := firstmoduledata.end
if p < procBrk {
p = procBrk
}
if mheap_.heapArenaAlloc.next <= p && p < mheap_.heapArenaAlloc.end {
p = mheap_.heapArenaAlloc.end
}
p = alignUp(p+(256<<10), heapArenaBytes)
/ Because we're worried about fragmentation on
/ 32-bit, we try to make a large initial reservation.
arenaSizes := []uintptr{
512 << 20,
256 << 20,
128 << 20,
}
for _, arenaSize := range arenaSizes {
a, size := sysReserveAligned(unsafe.Pointer(p), arenaSize, heapArenaBytes)
if a != nil {
mheap_.arena.init(uintptr(a), size, false)
p = mheap_.arena.end / For hint below
break
}
}
hint := (*arenaHint)(mheap_.arenaHintAlloc.alloc())
hint.addr = p
hint.next, mheap_.arenaHints = mheap_.arenaHints, hint
}
}
/ sysAlloc allocates heap arena space for at least n bytes. The
/ returned pointer is always heapArenaBytes-aligned and backed by
/ h.arenas metadata. The returned size is always a multiple of
/ heapArenaBytes. sysAlloc returns nil on failure.
/ There is no corresponding free function.
/
/ sysAlloc returns a memory region in the Reserved state. This region must
/ be transitioned to Prepared and then Ready before use.
/
/ h must be locked.
func (h *mheap) sysAlloc(n uintptr) (v unsafe.Pointer, size uintptr) {
assertLockHeld(&h.lock)
n = alignUp(n, heapArenaBytes)
/ First, try the arena pre-reservation.
/ Newly-used mappings are considered released.
v = h.arena.alloc(n, heapArenaBytes, &gcController.heapReleased)
if v != nil {
size = n
goto mapped
}
/ Try to grow the heap at a hint address.
for h.arenaHints != nil {
hint := h.arenaHints
p := hint.addr
if hint.down {
p -= n
}
if p+n < p {
/ We can't use this, so don't ask.
v = nil
} else if arenaIndex(p+n-1) >= 1<<arenaBits {
/ Outside addressable heap. Can't use.
v = nil
} else {
v = sysReserve(unsafe.Pointer(p), n)
}
if p == uintptr(v) {
/ Success. Update the hint.
if !hint.down {
p += n
}
hint.addr = p
size = n
break
}
/ Failed. Discard this hint and try the next.
/
/ TODO: This would be cleaner if sysReserve could be
/ told to only return the requested address. In
/ particular, this is already how Windows behaves, so
/ it would simplify things there.
if v != nil {
sysFreeOS(v, n)
}
h.arenaHints = hint.next
h.arenaHintAlloc.free(unsafe.Pointer(hint))
}
if size == 0 {
if raceenabled {
/ The race detector assumes the heap lives in
/ [0x00c000000000, 0x00e000000000), but we
/ just ran out of hints in this region. Give
/ a nice failure.
throw("too many address space collisions for -race mode")
}
/ All of the hints failed, so we'll take any
/ (sufficiently aligned) address the kernel will give
/ us.
v, size = sysReserveAligned(nil, n, heapArenaBytes)
if v == nil {
return nil, 0
}
/ Create new hints for extending this region.
hint := (*arenaHint)(h.arenaHintAlloc.alloc())
hint.addr, hint.down = uintptr(v), true
hint.next, mheap_.arenaHints = mheap_.arenaHints, hint
hint = (*arenaHint)(h.arenaHintAlloc.alloc())
hint.addr = uintptr(v) + size
hint.next, mheap_.arenaHints = mheap_.arenaHints, hint
}
/ Check for bad pointers or pointers we can't use.
{
var bad string
p := uintptr(v)
if p+size < p {
bad = "region exceeds uintptr range"
} else if arenaIndex(p) >= 1<<arenaBits {
bad = "base outside usable address space"
} else if arenaIndex(p+size-1) >= 1<<arenaBits {
bad = "end outside usable address space"
}
if bad != "" {
/ This should be impossible on most architectures,
/ but it would be really confusing to debug.
print("runtime: memory allocated by OS [", hex(p), ", ", hex(p+size), ") not in usable address space: ", bad, "\n")
throw("memory reservation exceeds address space limit")
}
}
if uintptr(v)&(heapArenaBytes-1) != 0 {
throw("misrounded allocation in sysAlloc")
}
mapped:
/ Create arena metadata.
for ri := arenaIndex(uintptr(v)); ri <= arenaIndex(uintptr(v)+size-1); ri++ {
l2 := h.arenas[ri.l1()]
if l2 == nil {
/ Allocate an L2 arena map.
/
/ Use sysAllocOS instead of sysAlloc or persistentalloc because there's no
/ statistic we can comfortably account for this space in. With this structure,
/ we rely on demand paging to avoid large overheads, but tracking which memory
/ is paged in is too expensive. Trying to account for the whole region means
/ that it will appear like an enormous memory overhead in statistics, even though
/ it is not.
l2 = (*[1 << arenaL2Bits]*heapArena)(sysAllocOS(unsafe.Sizeof(*l2)))
if l2 == nil {
throw("out of memory allocating heap arena map")
}
atomic.StorepNoWB(unsafe.Pointer(&h.arenas[ri.l1()]), unsafe.Pointer(l2))
}
if l2[ri.l2()] != nil {
throw("arena already initialized")
}
var r *heapArena
r = (*heapArena)(h.heapArenaAlloc.alloc(unsafe.Sizeof(*r), goarch.PtrSize, &memstats.gcMiscSys))
if r == nil {
r = (*heapArena)(persistentalloc(unsafe.Sizeof(*r), goarch.PtrSize, &memstats.gcMiscSys))
if r == nil {
throw("out of memory allocating heap arena metadata")
}
}
/ Add the arena to the arenas list.
if len(h.allArenas) == cap(h.allArenas) {
size := 2 * uintptr(cap(h.allArenas)) * goarch.PtrSize
if size == 0 {
size = physPageSize
}
newArray := (*notInHeap)(persistentalloc(size, goarch.PtrSize, &memstats.gcMiscSys))
if newArray == nil {
throw("out of memory allocating allArenas")
}
oldSlice := h.allArenas
*(*notInHeapSlice)(unsafe.Pointer(&h.allArenas)) = notInHeapSlice{newArray, len(h.allArenas), int(size / goarch.PtrSize)}
copy(h.allArenas, oldSlice)
/ Do not free the old backing array because
/ there may be concurrent readers. Since we
/ double the array each time, this can lead
/ to at most 2x waste.
}
h.allArenas = h.allArenas[:len(h.allArenas)+1]
h.allArenas[len(h.allArenas)-1] = ri
/ Store atomically just in case an object from the
/ new heap arena becomes visible before the heap lock
/ is released (which shouldn't happen, but there's
/ little downside to this).
atomic.StorepNoWB(unsafe.Pointer(&l2[ri.l2()]), unsafe.Pointer(r))
}
/ Tell the race detector about the new heap memory.
if raceenabled {
racemapshadow(v, size)
}
return
}
/ sysReserveAligned is like sysReserve, but the returned pointer is
/ aligned to align bytes. It may reserve either n or n+align bytes,
/ so it returns the size that was reserved.
func sysReserveAligned(v unsafe.Pointer, size, align uintptr) (unsafe.Pointer, uintptr) {
/ Since the alignment is rather large in uses of this
/ function, we're not likely to get it by chance, so we ask
/ for a larger region and remove the parts we don't need.
retries := 0
retry:
p := uintptr(sysReserve(v, size+align))
switch {
case p == 0:
return nil, 0
case p&(align-1) == 0:
/ We got lucky and got an aligned region, so we can
/ use the whole thing.
return unsafe.Pointer(p), size + align
case GOOS == "windows":
/ On Windows we can't release pieces of a
/ reservation, so we release the whole thing and
/ re-reserve the aligned sub-region. This may race,
/ so we may have to try again.
sysFreeOS(unsafe.Pointer(p), size+align)
p = alignUp(p, align)
p2 := sysReserve(unsafe.Pointer(p), size)
if p != uintptr(p2) {
/ Must have raced. Try again.
sysFreeOS(p2, size)
if retries++; retries == 100 {
throw("failed to allocate aligned heap memory; too many retries")
}
goto retry
}
/ Success.
return p2, size
default:
/ Trim off the unaligned parts.
pAligned := alignUp(p, align)
sysFreeOS(unsafe.Pointer(p), pAligned-p)
end := pAligned + size
endLen := (p + size + align) - end
if endLen > 0 {
sysFreeOS(unsafe.Pointer(end), endLen)
}
return unsafe.Pointer(pAligned), size
}
}
/ base address for all 0-byte allocations
var zerobase uintptr
/ nextFreeFast returns the next free object if one is quickly available.
/ Otherwise it returns 0.
func nextFreeFast(s *mspan) gclinkptr {
theBit := sys.Ctz64(s.allocCache) / Is there a free object in the allocCache?
if theBit < 64 {
result := s.freeindex + uintptr(theBit)
if result < s.nelems {
freeidx := result + 1
if freeidx%64 == 0 && freeidx != s.nelems {
return 0
}
s.allocCache >>= uint(theBit + 1)
s.freeindex = freeidx
s.allocCount++
return gclinkptr(result*s.elemsize + s.base())
}
}
return 0
}
/ nextFree returns the next free object from the cached span if one is available.
/ Otherwise it refills the cache with a span with an available object and
/ returns that object along with a flag indicating that this was a heavy
/ weight allocation. If it is a heavy weight allocation the caller must
/ determine whether a new GC cycle needs to be started or if the GC is active
/ whether this goroutine needs to assist the GC.
/
/ Must run in a non-preemptible context since otherwise the owner of
/ c could change.
func (c *mcache) nextFree(spc spanClass) (v gclinkptr, s *mspan, shouldhelpgc bool) {
s = c.alloc[spc]
shouldhelpgc = false
freeIndex := s.nextFreeIndex()
if freeIndex == s.nelems {
/ The span is full.
if uintptr(s.allocCount) != s.nelems {
println("runtime: s.allocCount=", s.allocCount, "s.nelems=", s.nelems)
throw("s.allocCount != s.nelems && freeIndex == s.nelems")
}
c.refill(spc)
shouldhelpgc = true
s = c.alloc[spc]
freeIndex = s.nextFreeIndex()
}
if freeIndex >= s.nelems {
throw("freeIndex is not valid")
}
v = gclinkptr(freeIndex*s.elemsize + s.base())
s.allocCount++
if uintptr(s.allocCount) > s.nelems {
println("s.allocCount=", s.allocCount, "s.nelems=", s.nelems)
throw("s.allocCount > s.nelems")
}
return
}
/ 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, needzero bool) unsafe.Pointer {
if gcphase == _GCmarktermination {
throw("mallocgc called with gcphase == _GCmarktermination")
}
if size == 0 {
return unsafe.Pointer(&zerobase)
}
userSize := size
if asanenabled {
/ Refer to ASAN runtime library, the malloc() function allocates extra memory,
/ the redzone, around the user requested memory region. And the redzones are marked
/ as unaddressable. We perform the same operations in Go to detect the overflows or
/ underflows.
size += computeRZlog(size)
}
if debug.malloc {
if debug.sbrk != 0 {
align := uintptr(16)
if typ != nil {
/ TODO(austin): This should be just
/ align = uintptr(typ.align)
/ but that's only 4 on 32-bit platforms,
/ even if there's a uint64 field in typ (see #599).
/ This causes 64-bit atomic accesses to panic.
/ Hence, we use stricter alignment that matches
/ the normal allocator better.
if size&7 == 0 {
align = 8
} else if size&3 == 0 {
align = 4
} else if size&1 == 0 {
align = 2
} else {
align = 1
}
}
return persistentalloc(size, align, &memstats.other_sys)
}
if inittrace.active && inittrace.id == getg().goid {
/ Init functions are executed sequentially in a single goroutine.
inittrace.allocs += 1
}
}
/ 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 := userSize
c := getMCache(mp)
if c == nil {
throw("mallocgc called without a P or outside bootstrapping")
}
var span *mspan
var x unsafe.Pointer
noscan := typ == nil || typ.ptrdata == 0
/ In some cases block zeroing can profitably (for latency reduction purposes)
/ be delayed till preemption is possible; delayedZeroing tracks that state.
delayedZeroing := false
if size <= maxSmallSize {
if noscan && 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 noscan (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 = alignUp(off, 8)
} 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.
x = unsafe.Pointer(c.tiny + off)
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)
if v == 0 {
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.tiny = uintptr(x)
c.tinyoffset = size
}
size = maxTinySize
} else {
var sizeclass uint8
if size <= smallSizeMax-8 {
sizeclass = size_to_class8[divRoundUp(size, smallSizeDiv)]
} else {
sizeclass = size_to_class128[divRoundUp(size-smallSizeMax, largeSizeDiv)]
}
size = uintptr(class_to_size[sizeclass])
spc := makeSpanClass(sizeclass, noscan)
span = c.alloc[spc]
v := nextFreeFast(span)
if v == 0 {
v, span, shouldhelpgc = c.nextFree(spc)
}
x = unsafe.Pointer(v)
if needzero && span.needzero != 0 {
memclrNoHeapPointers(unsafe.Pointer(v), size)
}
}
} else {
shouldhelpgc = true
/ 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
if !noscan {
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
}
} else {
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()
/ Allocate black during GC.
/ 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 != _GCoff {
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() {
gcStart(t)
}
}
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)
}
return x
}
/ 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)
}
}
/ implementation of new builtin
/ 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 {
return newarray(typ, n)
}
func profilealloc(mp *m, x unsafe.Pointer, size uintptr) {
c := getMCache(mp)
if c == nil {
throw("profilealloc called without a P or outside bootstrapping")
}
c.nextSample = nextSample()
mProf_Malloc(x, size)
}
/ 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.
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()
}
}
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.
switch {
case mean > 0x7000000:
mean = 0x7000000
case mean == 0:
return 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
const randomBitCount = 26
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.
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.
/ sysStat must be non-nil.
/
/ 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
}
}
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))
}
return p
}
/ 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.
n := pEnd - l.mapped
sysMap(unsafe.Pointer(l.mapped), n, sysStat)
sysUsed(unsafe.Pointer(l.mapped), n, n)
}
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))
}
/ 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
}
}