golang内存分配概述
golang内存分配概述
golang的内存分配机制主要类似于tcmalloc机制，来快速高效的分配与管理内存，从而高效分配与管理内存。
有关 tcmalloc 的详细资料大家可参考官网，简单概括就是通过预先分配一个大的堆，每个线程都管理一块小内存的对象列表，大对象都是直接通过堆来直接管理，每个线程申请内存的时候如果小对象就直接在堆上分配，大对象就通过堆分配，每个内存都可以再堆上管理到。大家有兴趣课详细看一个官网的介绍，golang的内存分配也是按照如上原理来实现的，大概了解了tcmalloc的流程就很好理解golang的内存分配流程。
golang内存分配理解
go运行时的内存布局，相关的理解如下（基于go1.12版本）；
- 在go启动的时候，会生成一个全局唯一的heap_对象，然后通过该对象来管理与分配内存。
- 在heap_中arenas是通过操作系统申请分配的内存，并且heap中保存了golang定义的不同大小的mspan对象。
- 在go的启动过程中每一个M都会生成一个唯一的mache对象，来分配在M运行过程中申请的小对象或者微小对象。
- 在go中内存管理的单位为mspan，默认管理8KB的page大小，通过分配的对象的大小不同而调整将管理的内存分配多个pages，所有的最终的数据都保存在mspan中，可以在heap中统一管理。
- 在go中，预先定义好了一些微小对象和小对象的大小定义，并分配给了central中，在mcache中申请对应的spanClass的时候，该大小的内存时会通过central来分配，如果是大对象分配则直接分配到heap上，通过arenas来分配管理。
微小对象与小对象
// class bytes/obj bytes/span objects tail waste max waste
// 1 8 8192 1024 0 87.50%
// 2 16 8192 512 0 43.75%
// 3 32 8192 256 0 46.88%
// 4 48 8192 170 32 31.52%
// 5 64 8192 128 0 23.44%
// 6 80 8192 102 32 19.07%
// 7 96 8192 85 32 15.95%
// 8 112 8192 73 16 13.56%
// 9 128 8192 64 0 11.72%
// 10 144 8192 56 128 11.82%
// 11 160 8192 51 32 9.73%
// 12 176 8192 46 96 9.59%
// 13 192 8192 42 128 9.25%
// 14 208 8192 39 80 8.12%
// 15 224 8192 36 128 8.15%
// 16 240 8192 34 32 6.62%
// 17 256 8192 32 0 5.86%
// 18 288 8192 28 128 12.16%
// 19 320 8192 25 192 11.80%
// 20 352 8192 23 96 9.88%
// 21 384 8192 21 128 9.51%
// 22 416 8192 19 288 10.71%
// 23 448 8192 18 128 8.37%
// 24 480 8192 17 32 6.82%
// 25 512 8192 16 0 6.05%
// 26 576 8192 14 128 12.33%
// 27 640 8192 12 512 15.48%
// 28 704 8192 11 448 13.93%
// 29 768 8192 10 512 13.94%
// 30 896 8192 9 128 15.52%
// 31 1024 8192 8 0 12.40%
// 32 1152 8192 7 128 12.41%
// 33 1280 8192 6 512 15.55%
// 34 1408 16384 11 896 14.00%
// 35 1536 8192 5 512 14.00%
// 36 1792 16384 9 256 15.57%
// 37 2048 8192 4 0 12.45%
// 38 2304 16384 7 256 12.46%
// 39 2688 8192 3 128 15.59%
// 40 3072 24576 8 0 12.47%
// 41 3200 16384 5 384 6.22%
// 42 3456 24576 7 384 8.83%
// 43 4096 8192 2 0 15.60%
// 44 4864 24576 5 256 16.65%
// 45 5376 16384 3 256 10.92%
// 46 6144 24576 4 0 12.48%
// 47 6528 32768 5 128 6.23%
// 48 6784 40960 6 256 4.36%
// 49 6912 49152 7 768 3.37%
// 50 8192 8192 1 0 15.61%
// 51 9472 57344 6 512 14.28%
// 52 9728 49152 5 512 3.64%
// 53 10240 40960 4 0 4.99%
// 54 10880 32768 3 128 6.24%
// 55 12288 24576 2 0 11.45%
// 56 13568 40960 3 256 9.99%
// 57 14336 57344 4 0 5.35%
// 58 16384 16384 1 0 12.49%
// 59 18432 73728 4 0 11.11%
// 60 19072 57344 3 128 3.57%
// 61 20480 40960 2 0 6.87%
// 62 21760 65536 3 256 6.25%
// 63 24576 24576 1 0 11.45%
// 64 27264 81920 3 128 10.00%
// 65 28672 57344 2 0 4.91%
// 66 32768 32768 1 0 12.50%
位于sizeclasses.go中的文件描述了不同大小的文件，总共有67中大小，假如objects大小为1024字节则8192字节刚刚好可以分配个八个对象使用，最坏的情况就是只保存了一个对象即最大浪费率为87.5%，如果刚刚好保存了八个对象则没有任何浪费。在go程序中分配对象的时候都会通过计算一下对象的大小，如果在这个列表来计算对象保存的spanClass。
分配内存newobject
分配内存的过程主要分三种情况，都集中在mallocgc这个函数中。
// 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 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 = 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.
span := c.alloc[tinySpanClass]
v := nextFreeFast(span)
if v == 0 {
v, _, 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 size < c.tinyoffset || c.tiny == 0 {
c.tiny = uintptr(x)
c.tinyoffset = size
}
size = maxTinySize
} else {
var sizeclass uint8
if size <= smallSizeMax-8 {
sizeclass = size_to_class8[(size+smallSizeDiv-1)/smallSizeDiv]
} else {
sizeclass = size_to_class128[(size-smallSizeMax+largeSizeDiv-1)/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 {
var s *mspan
shouldhelpgc = true
systemstack(func() {
s = largeAlloc(size, needzero, noscan)
})
s.freeindex = 1
s.allocCount = 1
x = unsafe.Pointer(s.base())
size = s.elemsize
}
...
}
- 分配对象内存大小是否小于16字节，如果小于16字节直接通过Tiny allocator分配。
- 分配对象大于等于16字节小于等于32KB，通过小对象快速分配来分配空间。
- 分配大于32KB的空间时，直接使用largeAlloc来分配一个mspan来进行分配。
Tiny allocator分配
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.
span := c.alloc[tinySpanClass]
v := nextFreeFast(span)
if v == 0 {
v, _, 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 size < c.tinyoffset || c.tiny == 0 {
c.tiny = uintptr(x)
c.tinyoffset = size
}
size = maxTinySize
首先查看当前tiny分配的偏移位置，如果当前偏移位置可以容下待分配的大小则直接分配到该位置，否则则通过alloc来获取一块新的内存块大小来进行分配。
小对象
var sizeclass uint8
if size <= smallSizeMax-8 {
sizeclass = size_to_class8[(size+smallSizeDiv-1)/smallSizeDiv]
} else {
sizeclass = size_to_class128[(size-smallSizeMax+largeSizeDiv-1)/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)
}
先检查计算当前对象的size，获取当前的spanClass的值，然后再去快速找到一块span来分配内存，首先先快速去查找该span是否有空闲的，如果有空闲的则标记为空闲并返回该空闲的span，否则就通过c.nextFree来分配一个新的内存空间。
// 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() // 获取下一个free的index
if freeIndex == s.nelems { // 如果当前的spanClass元素已经满了则调用refill来重新拿到一个空闲的span
// 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
}
如果当前分配的元素已经满了则通过refill函数来拿到一个新的空闲空间；
// refill acquires a new span of span class spc for c. This span will
// have at least one free object. The current span in c must be full.
//
// Must run in a non-preemptible context since otherwise the owner of
// c could change.
func (c *mcache) refill(spc spanClass) {
// Return the current cached span to the central lists.
s := c.alloc[spc]
if uintptr(s.allocCount) != s.nelems {
throw("refill of span with free space remaining")
}
if s != &emptymspan {
// Mark this span as no longer cached.
if s.sweepgen != mheap_.sweepgen+3 {
throw("bad sweepgen in refill")
}
atomic.Store(&s.sweepgen, mheap_.sweepgen)
}
// Get a new cached span from the central lists.
s = mheap_.central[spc].mcentral.cacheSpan()
if s == nil {
throw("out of memory")
}
if uintptr(s.allocCount) == s.nelems {
throw("span has no free space")
}
// Indicate that this span is cached and prevent asynchronous
// sweeping in the next sweep phase.
s.sweepgen = mheap_.sweepgen + 3
c.alloc[spc] = s
}
通过cacheSpan函数来获取最新一块的内存
// Allocate a span to use in an mcache.
func (c *mcentral) cacheSpan() *mspan {
// Deduct credit for this span allocation and sweep if necessary.
spanBytes := uintptr(class_to_allocnpages[c.spanclass.sizeclass()]) * _PageSize
deductSweepCredit(spanBytes, 0)
lock(&c.lock)
traceDone := false
if trace.enabled {
traceGCSweepStart()
}
sg := mheap_.sweepgen
retry:
var s *mspan
for s = c.nonempty.first; s != nil; s = s.next { // 获取非空闲的列表头部
if s.sweepgen == sg-2 && atomic.Cas(&s.sweepgen, sg-2, sg-1) { // 检查当前是否空闲
c.nonempty.remove(s) // 如果空闲则从该列表中移除 加入到空闲列表中 然后跳转到havespan进行后续处理
c.empty.insertBack(s)
unlock(&c.lock)
s.sweep(true)
goto havespan
}
if s.sweepgen == sg-1 {
// the span is being swept by background sweeper, skip
continue
}
// we have a nonempty span that does not require sweeping, allocate from it
c.nonempty.remove(s) // 因为最少有一个元素可以用所以就使用该span
c.empty.insertBack(s)
unlock(&c.lock)
goto havespan
}
for s = c.empty.first; s != nil; s = s.next { // 检查空列表 等待sweep
if s.sweepgen == sg-2 && atomic.Cas(&s.sweepgen, sg-2, sg-1) {
// we have an empty span that requires sweeping,
// sweep it and see if we can free some space in it
c.empty.remove(s)
// swept spans are at the end of the list
c.empty.insertBack(s)
unlock(&c.lock)
s.sweep(true)
freeIndex := s.nextFreeIndex()
if freeIndex != s.nelems {
s.freeindex = freeIndex
goto havespan
}
lock(&c.lock)
// the span is still empty after sweep
// it is already in the empty list, so just retry
goto retry
}
if s.sweepgen == sg-1 {
// the span is being swept by background sweeper, skip
continue
}
// already swept empty span,
// all subsequent ones must also be either swept or in process of sweeping
break
}
if trace.enabled {
traceGCSweepDone()
traceDone = true
}
unlock(&c.lock)
// Replenish central list if empty.
s = c.grow() // 如果一直没有找到则想heap中申请内存
if s == nil {
return nil
}
lock(&c.lock)
c.empty.insertBack(s) // 插入新申请到的span
unlock(&c.lock)
// At this point s is a non-empty span, queued at the end of the empty list,
// c is unlocked.
havespan:
if trace.enabled && !traceDone {
traceGCSweepDone()
}
n := int(s.nelems) - int(s.allocCount)
if n == 0 || s.freeindex == s.nelems || uintptr(s.allocCount) == s.nelems {
throw("span has no free objects")
}
// Assume all objects from this span will be allocated in the
// mcache. If it gets uncached, we'll adjust this.
atomic.Xadd64(&c.nmalloc, int64(n))
usedBytes := uintptr(s.allocCount) * s.elemsize
atomic.Xadd64(&memstats.heap_live, int64(spanBytes)-int64(usedBytes))
if trace.enabled {
// heap_live changed.
traceHeapAlloc()
}
if gcBlackenEnabled != 0 {
// heap_live changed.
gcController.revise()
}
freeByteBase := s.freeindex &^ (64 - 1)
whichByte := freeByteBase / 8
// Init alloc bits cache.
s.refillAllocCache(whichByte)
// Adjust the allocCache so that s.freeindex corresponds to the low bit in
// s.allocCache.
s.allocCache >>= s.freeindex % 64
return s
}
通过在列表中进行查找，查看是否有空闲可用的span，如果没有找到则申请一个新的span来使用。
大对象
var s *mspan
shouldhelpgc = true
systemstack(func() {
s = largeAlloc(size, needzero, noscan)
})
s.freeindex = 1
s.allocCount = 1
x = unsafe.Pointer(s.base())
size = s.elemsize
主要就是通过largeAlloc来分配内存，
func largeAlloc(size uintptr, needzero bool, noscan bool) *mspan {
// print("largeAlloc size=", size, "\n")
if size+_PageSize < size { // 检查是否oom
throw("out of memory")
}
npages := size >> _PageShift // 将当前的大小转换成页数
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, makeSpanClass(0, noscan), true, needzero) // 申请对应的页数内存
if s == nil {
throw("out of memory")
}
s.limit = s.base() + size // 增加边界值
heapBitsForAddr(s.base()).initSpan(s) // 初始化heapBits的值
return s
}
此时通过mheap_的alloc来申请内存；
// alloc allocates a new span of npage pages from the GC'd heap.
//
// Either large must be true or spanclass must indicates the span's
// size class and scannability.
//
// If needzero is true, the memory for the returned span will be zeroed.
func (h *mheap) alloc(npage uintptr, spanclass spanClass, large bool, needzero bool) *mspan {
// Don't do any operations that lock the heap on the G stack.
// It might trigger stack growth, and the stack growth code needs
// to be able to allocate heap.
var s *mspan
systemstack(func() {
s = h.alloc_m(npage, spanclass, large) // 申请内存
})
if s != nil {
if needzero && s.needzero != 0 {
memclrNoHeapPointers(unsafe.Pointer(s.base()), s.npages<<_PageShift)
}
s.needzero = 0
}
return s
}
在go栈上调用alloc_m申请内存
func (h *mheap) alloc_m(npage uintptr, spanclass spanClass, large bool) *mspan {
_g_ := getg()
// To prevent excessive heap growth, before allocating n pages
// we need to sweep and reclaim at least n pages.
if h.sweepdone == 0 {
h.reclaim(npage)
}
lock(&h.lock)
// transfer stats from cache to global
memstats.heap_scan += uint64(_g_.m.mcache.local_scan)
_g_.m.mcache.local_scan = 0
memstats.tinyallocs += uint64(_g_.m.mcache.local_tinyallocs)
_g_.m.mcache.local_tinyallocs = 0
s := h.allocSpanLocked(npage, &memstats.heap_inuse) // 先上heap锁然后申请内存
if s != nil {
// Record span info, because gc needs to be
// able to map interior pointer to containing span.
atomic.Store(&s.sweepgen, h.sweepgen) // 保存申请到的span
h.sweepSpans[h.sweepgen/2%2].push(s) // Add to swept in-use list.
s.state = mSpanInUse // 更新状态
s.allocCount = 0
s.spanclass = spanclass
if sizeclass := spanclass.sizeclass(); sizeclass == 0 {
s.elemsize = s.npages << _PageShift
s.divShift = 0
s.divMul = 0
s.divShift2 = 0
s.baseMask = 0
} else {
s.elemsize = uintptr(class_to_size[sizeclass])
m := &class_to_divmagic[sizeclass]
s.divShift = m.shift
s.divMul = m.mul
s.divShift2 = m.shift2
s.baseMask = m.baseMask
}
// Mark in-use span in arena page bitmap.
arena, pageIdx, pageMask := pageIndexOf(s.base()) // 在arena中加入该span 并标记在使用
arena.pageInUse[pageIdx] |= pageMask
// update stats, sweep lists
h.pagesInUse += uint64(npage)
if large {
memstats.heap_objects++
mheap_.largealloc += uint64(s.elemsize)
mheap_.nlargealloc++
atomic.Xadd64(&memstats.heap_live, int64(npage<<_PageShift))
}
}
...
return s
}
继续查看allocSpanLocked函数；
// Allocates a span of the given size. h must be locked.
// The returned span has been removed from the
// free structures, but its state is still mSpanFree.
func (h *mheap) allocSpanLocked(npage uintptr, stat *uint64) *mspan {
var s *mspan
s = h.pickFreeSpan(npage) // 先检查是否有这么多空闲的业务
if s != nil {
goto HaveSpan // 如果有则不用分配
}
// On failure, grow the heap and try again.
if !h.grow(npage) { // 申请空间
return nil
}
s = h.pickFreeSpan(npage) // 再尝试获取新的内存
if s != nil {
goto HaveSpan
}
throw("grew heap, but no adequate free span found")
HaveSpan:
// Mark span in use.
if s.state != mSpanFree {
throw("candidate mspan for allocation is not free")
}
if s.npages < npage {
throw("candidate mspan for allocation is too small")
}
// First, subtract any memory that was released back to
// the OS from s. We will re-scavenge the trimmed section
// if necessary.
memstats.heap_released -= uint64(s.released())
if s.npages > npage { // 如果获取的页数比需要分配的多 则分割剩余的页数放入另外一个span中
// Trim extra and put it back in the heap.
t := (*mspan)(h.spanalloc.alloc())
t.init(s.base()+npage<<_PageShift, s.npages-npage)
s.npages = npage
h.setSpan(t.base()-1, s)
h.setSpan(t.base(), t)
h.setSpan(t.base()+t.npages*pageSize-1, t)
t.needzero = s.needzero
// If s was scavenged, then t may be scavenged.
start, end := t.physPageBounds()
if s.scavenged && start < end {
memstats.heap_released += uint64(end - start)
t.scavenged = true
}
s.state = mSpanManual // prevent coalescing with s
t.state = mSpanManual
h.freeSpanLocked(t, false, false, s.unusedsince)
s.state = mSpanFree
}
// "Unscavenge" s only AFTER splitting so that
// we only sysUsed whatever we actually need.
if s.scavenged {
// sysUsed all the pages that are actually available
// in the span. Note that we don't need to decrement
// heap_released since we already did so earlier.
sysUsed(unsafe.Pointer(s.base()), s.npages<<_PageShift)
s.scavenged = false
}
s.unusedsince = 0
h.setSpans(s.base(), npage, s)
*stat += uint64(npage << _PageShift)
memstats.heap_idle -= uint64(npage << _PageShift)
//println("spanalloc", hex(s.start<<_PageShift))
if s.inList() {
throw("still in list")
}
return s
}
此时查看grow函数的流程
// Try to add at least npage pages of memory to the heap,
// returning whether it worked.
//
// h must be locked.
func (h *mheap) grow(npage uintptr) bool {
ask := npage << _PageShift // 获取对应页数的实际内存大小
v, size := h.sysAlloc(ask) //调用sysAlloc分配指定大小的内存
if v == nil {
print("runtime: out of memory: cannot allocate ", ask, "-byte block (", memstats.heap_sys, " in use)\n")
return false
}
// Scavenge some pages out of the free treap to make up for
// the virtual memory space we just allocated. We prefer to
// scavenge the largest spans first since the cost of scavenging
// is proportional to the number of sysUnused() calls rather than
// the number of pages released, so we make fewer of those calls
// with larger spans.
h.scavengeLargest(size)
// Create a fake "in use" span and free it, so that the
// right coalescing happens.
s := (*mspan)(h.spanalloc.alloc()) // 获取一个span
s.init(uintptr(v), size/pageSize) // 初始化对应的span大小
h.setSpans(s.base(), s.npages, s)
atomic.Store(&s.sweepgen, h.sweepgen)
s.state = mSpanInUse
h.pagesInUse += uint64(s.npages) // 标记为可用
h.freeSpanLocked(s, false, true, 0)
return true
}
至此，三个不同大小的分配的主要过程基本上描述完成。
总结
go的内存分配机制与tcmalloc原理基本类似，使用过程也比较类似，通过不同线程缓存的cache来分配内存，通过唯一的heap来分配管理内存，heap通过全局的缓存的spanClass的对象来进行小对象的快速分配，提高全局分配内存的响应速度，如果是大对象则直接进行对象的分配管理。由于本人才疏学浅，如有错误请批评指正。