return sysAllocOS(n)
}

// sysUnused transitions a memory region from Ready to Prepared. It notifies the
// operating system that the physical pages backing this memory region are no
// longer needed and can be reused for other purposes. The contents of a
// sysUnused memory region are considered forfeit and the region must not be
// accessed again until sysUsed is called.
func sysUnused(v unsafe.Pointer, n uintptr) {

		n -= small
	}
}

func sysUsedOS(v unsafe.Pointer, n uintptr) {
	p := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
	if p == uintptr(v) {
		return
	}

	// Commit failed. See SysUnused.
	// Hold on to n here so we can give back a better error message
	// for certain cases.
	k := n
	for k > 0 {
		small := k

		// madvise will round this to any physical page
		// *covered* by this range, so an unaligned madvise
		// will release more memory than intended.
		throw("unaligned sysUnused")
	}

	advise := atomic.Load(&adviseUnused)
	if debug.madvdontneed != 0 && advise != madviseUnsupported {
		advise = _MADV_DONTNEED
	}
	switch advise {
	case _MADV_FREE:
		if madvise(v, n, _MADV_FREE) == 0 {

			// With that done, it's safe to unlock.
			unlock(p.mheapLock)

			if !p.test {
				// Only perform sys* operations if we're not in a test.
				// It's dangerous to do so otherwise.
				sysUnused(unsafe.Pointer(addr), uintptr(npages)*pageSize)

				// Update global accounting only when not in test, otherwise
				// the runtime's accounting will be wrong.
				nbytes := int64(npages * pageSize)

		if need.size() == 0 {
			continue
		}

		// Map and commit need.
		sysMap(unsafe.Pointer(need.base.addr()), need.size(), p.sysStat)
		sysUsed(unsafe.Pointer(need.base.addr()), need.size(), need.size())
		p.summaryMappedReady += need.size()
	}

	// Update the scavenge index.
	p.summaryMappedReady += p.scav.index.sysGrow(base, limit, p.sysStat)
}

	if reservation == nil {
		throw("failed to reserve page summary memory")
	}
	// There isn't much. Just map it and mark it as used immediately.
	sysMap(reservation, totalSize, p.sysStat)
	sysUsed(reservation, totalSize, totalSize)
	p.summaryMappedReady += totalSize

	// Iterate over the reservation and cut it up into slices.
	//
	// Maintain i as the byte offset from reservation where

	// Commit and account for any scavenged memory that the span now owns.
	nbytes := npages * pageSize
	if scav != 0 {
		// sysUsed all the pages that are actually available
		// in the span since some of them might be scavenged.
		sysUsed(unsafe.Pointer(base), nbytes, scav)
		gcController.heapReleased.add(-int64(scav))
	}
	// Update stats.
	gcController.heapFree.add(-int64(nbytes - scav))

	//
	// Unlike (*mheap).grow, just map in everything that we
	// asked for. We're likely going to use it all.
	sysMap(unsafe.Pointer(base), userArenaChunkBytes, &gcController.heapReleased)
	sysUsed(unsafe.Pointer(base), userArenaChunkBytes, userArenaChunkBytes)

	// Model the user arena as a heap span for a large object.
	spc := makeSpanClass(0, false)
	h.initSpan(s, spanAllocHeap, spc, base, userArenaChunkPages)

	// Free extra data structures.
	sysFreeOS(unsafe.Pointer(&p.scav.index.chunks[0]), uintptr(cap(p.scav.index.chunks))*unsafe.Sizeof(atomicScavChunkData{}))

	// Subtract back out whatever we mapped for the summaries.
	// sysUsed adds to p.sysStat and memstats.mappedReady no matter what
	// (and in anger should actually be accounted for), and there's no other
	// way to figure out how much we actually mapped.

	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.