}
}

// grow allocates a new empty span from the heap and initializes it for c's size class.
func (c *mcentral) grow() *mspan {
	npages := uintptr(class_to_allocnpages[c.spanclass.sizeclass()])
	size := uintptr(class_to_size[c.spanclass.sizeclass()])

	s := mheap_.alloc(npages, c.spanclass)
	if s == nil {
		return nil
	}

	// Use division by multiplication and shifts to quickly compute:

	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			v := new(int)
			runtime.SetFinalizer(v, fin)
		}
	})
}

// One chunk must be exactly one sizeclass in size.
// It should be a sizeclass not used much by others, so we
// have a greater chance of finding adjacent ones.
// size class 19: 320 byte objects, 25 per page, 1 page alloc at a time
const objsize = 320

		// Count up how many slots were used and record it.
		stats := memstats.heapStats.acquire()
		slotsUsed := int64(s.allocCount) - int64(s.allocCountBeforeCache)
		atomic.Xadd64(&stats.smallAllocCount[spc.sizeclass()], slotsUsed)

		// Flush tinyAllocs.
		if spc == tinySpanClass {
			atomic.Xadd64(&stats.tinyAllocCount, int64(c.tinyAllocs))
			c.tinyAllocs = 0
		}
		memstats.heapStats.release()

		// since we're not holding the heap lock.
		s.spanclass = spanclass
		if sizeclass := spanclass.sizeclass(); sizeclass == 0 {
			s.elemsize = nbytes
			s.nelems = 1
			s.divMul = 0
		} else {
			s.elemsize = uintptr(class_to_size[sizeclass])
			if !s.spanclass.noscan() && heapBitsInSpan(s.elemsize) {
				// Reserve space for the pointer/scan bitmap at the end.

		// so wasted space is at most 12.5%.
		allocsize := pageSize
		for allocsize%size > allocsize/8 {
			allocsize += pageSize
		}
		npages := allocsize / pageSize

		// If the previous sizeclass chose the same
		// allocation size and fit the same number of
		// objects into the page, we might as well
		// use just this size instead of having two
		// different sizes.

				continue
			}
			if s.isUnusedUserArenaChunk() {
				continue
			}
			if sizeclass := s.spanclass.sizeclass(); sizeclass == 0 {
				slow.Mallocs++
				slow.Alloc += uint64(s.elemsize)
			} else {
				slow.Mallocs += uint64(s.allocCount)
				slow.Alloc += uint64(s.allocCount) * uint64(s.elemsize)
				bySize[sizeclass].Mallocs += uint64(s.allocCount)
			}
		}

			if hasHeader {
				size += mallocHeaderSize
			}
			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)

			}
			lock(&mheap_.lock)
			mheap_.userArena.quarantineList.remove(s)
			mheap_.userArena.readyList.insert(s)
			unlock(&mheap_.lock)
		})
		return false
	}

	if spc.sizeclass() != 0 {
		// Handle spans for small objects.
		if nfreed > 0 {
			// Only mark the span as needing zeroing if we've freed any
			// objects, because a fresh span that had been allocated into,

		}
		throw("runtime.SetFinalizer: pointer not in allocated block")
	}

	// Move base forward if we've got an allocation header.
	if !span.spanclass.noscan() && !heapBitsInSpan(span.elemsize) && span.spanclass.sizeclass() != 0 {
		base += mallocHeaderSize
	}

	if uintptr(e.data) != base {
		// As an implementation detail we allow to set finalizers for an inner byte

		// Handle header-less objects.
		return typePointers{elem: addr, addr: addr, mask: span.heapBitsSmallForAddr(addr)}
	}

	// All of these objects have a header.
	var typ *_type
	if spc.sizeclass() != 0 {
		// Pull the allocation header from the first word of the object.
		typ = *(**_type)(unsafe.Pointer(addr))
		addr += mallocHeaderSize
	} else {
		typ = span.largeType
		if typ == nil {