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// Copyright 2019 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.
// Address range data structure.
// This file contains an implementation of a data structure which
// manages ordered address ranges.
package runtime
import (
// addrRange represents a region of address space.
// An addrRange must never span a gap in the address space.
type addrRange struct {
// base and limit together represent the region of address space
// [base, limit). That is, base is inclusive, limit is exclusive.
// These are address over an offset view of the address space on
// platforms with a segmented address space, that is, on platforms
// where arenaBaseOffset != 0.
base, limit offAddr
// makeAddrRange creates a new address range from two virtual addresses.
// Throws if the base and limit are not in the same memory segment.
func makeAddrRange(base, limit uintptr) addrRange {
r := addrRange{offAddr{base}, offAddr{limit}}
if (base-arenaBaseOffset >= base) != (limit-arenaBaseOffset >= limit) {
throw("addr range base and limit are not in the same memory segment")
return r
// size returns the size of the range represented in bytes.
func (a addrRange) size() uintptr {
if !a.base.lessThan(a.limit) {
return 0
// Subtraction is safe because limit and base must be in the same
// segment of the address space.
return a.limit.diff(a.base)
// contains returns whether or not the range contains a given address.
func (a addrRange) contains(addr uintptr) bool {
return a.base.lessEqual(offAddr{addr}) && (offAddr{addr}).lessThan(a.limit)
// subtract takes the addrRange toPrune and cuts out any overlap with
// from, then returns the new range. subtract assumes that a and b
// either don't overlap at all, only overlap on one side, or are equal.
// If b is strictly contained in a, thus forcing a split, it will throw.
func (a addrRange) subtract(b addrRange) addrRange {
if b.base.lessEqual(a.base) && a.limit.lessEqual(b.limit) {
return addrRange{}
} else if a.base.lessThan(b.base) && b.limit.lessThan(a.limit) {
throw("bad prune")
} else if b.limit.lessThan(a.limit) && a.base.lessThan(b.limit) {
a.base = b.limit
} else if a.base.lessThan(b.base) && b.base.lessThan(a.limit) {
a.limit = b.base
return a
// removeGreaterEqual removes all addresses in a greater than or equal
// to addr and returns the new range.
func (a addrRange) removeGreaterEqual(addr uintptr) addrRange {
if (offAddr{addr}).lessEqual(a.base) {
return addrRange{}
if a.limit.lessEqual(offAddr{addr}) {
return a
return makeAddrRange(a.base.addr(), addr)
var (
// minOffAddr is the minimum address in the offset space, and
// it corresponds to the virtual address arenaBaseOffset.
minOffAddr = offAddr{arenaBaseOffset}
// maxOffAddr is the maximum address in the offset address
// space. It corresponds to the highest virtual address representable
// by the page alloc chunk and heap arena maps.
maxOffAddr = offAddr{(((1 << heapAddrBits) - 1) + arenaBaseOffset) & uintptrMask}
// offAddr represents an address in a contiguous view
// of the address space on systems where the address space is
// segmented. On other systems, it's just a normal address.
type offAddr struct {
// a is just the virtual address, but should never be used
// directly. Call addr() to get this value instead.
a uintptr
// add adds a uintptr offset to the offAddr.
func (l offAddr) add(bytes uintptr) offAddr {
return offAddr{a: l.a + bytes}
// sub subtracts a uintptr offset from the offAddr.
func (l offAddr) sub(bytes uintptr) offAddr {
return offAddr{a: l.a - bytes}
// diff returns the amount of bytes in between the
// two offAddrs.
func (l1 offAddr) diff(l2 offAddr) uintptr {
return l1.a - l2.a
// lessThan returns true if l1 is less than l2 in the offset
// address space.
func (l1 offAddr) lessThan(l2 offAddr) bool {
return (l1.a - arenaBaseOffset) < (l2.a - arenaBaseOffset)
// lessEqual returns true if l1 is less than or equal to l2 in
// the offset address space.
func (l1 offAddr) lessEqual(l2 offAddr) bool {
return (l1.a - arenaBaseOffset) <= (l2.a - arenaBaseOffset)
// equal returns true if the two offAddr values are equal.
func (l1 offAddr) equal(l2 offAddr) bool {
// No need to compare in the offset space, it
// means the same thing.
return l1 == l2
// addr returns the virtual address for this offset address.
func (l offAddr) addr() uintptr {
return l.a
// addrRanges is a data structure holding a collection of ranges of
// address space.
// The ranges are coalesced eagerly to reduce the
// number ranges it holds.
// The slice backing store for this field is persistentalloc'd
// and thus there is no way to free it.
// addrRanges is not thread-safe.
type addrRanges struct {
// ranges is a slice of ranges sorted by base.
ranges []addrRange
// totalBytes is the total amount of address space in bytes counted by
// this addrRanges.
totalBytes uintptr
// sysStat is the stat to track allocations by this type
sysStat *uint64
func (a *addrRanges) init(sysStat *uint64) {
ranges := (*notInHeapSlice)(unsafe.Pointer(&a.ranges))
ranges.len = 0
ranges.cap = 16
ranges.array = (*notInHeap)(persistentalloc(unsafe.Sizeof(addrRange{})*uintptr(ranges.cap), sys.PtrSize, sysStat))
a.sysStat = sysStat
a.totalBytes = 0
// findSucc returns the first index in a such that base is
// less than the base of the addrRange at that index.
func (a *addrRanges) findSucc(addr uintptr) int {
// TODO(mknyszek): Consider a binary search for large arrays.
// While iterating over these ranges is potentially expensive,
// the expected number of ranges is small, ideally just 1,
// since Go heaps are usually mostly contiguous.
base := offAddr{addr}
for i := range a.ranges {
if base.lessThan(a.ranges[i].base) {
return i
return len(a.ranges)
// findAddrGreaterEqual returns the smallest address represented by a
// that is >= addr. Thus, if the address is represented by a,
// then it returns addr. The second return value indicates whether
// such an address exists for addr in a. That is, if addr is larger than
// any address known to a, the second return value will be false.
func (a *addrRanges) findAddrGreaterEqual(addr uintptr) (uintptr, bool) {
i := a.findSucc(addr)
if i == 0 {
return a.ranges[0].base.addr(), true
if a.ranges[i-1].contains(addr) {
return addr, true
if i < len(a.ranges) {
return a.ranges[i].base.addr(), true
return 0, false
// contains returns true if a covers the address addr.
func (a *addrRanges) contains(addr uintptr) bool {
i := a.findSucc(addr)
if i == 0 {
return false
return a.ranges[i-1].contains(addr)
// add inserts a new address range to a.
// r must not overlap with any address range in a.
func (a *addrRanges) add(r addrRange) {
// The copies in this function are potentially expensive, but this data
// structure is meant to represent the Go heap. At worst, copying this
// would take ~160µs assuming a conservative copying rate of 25 GiB/s (the
// copy will almost never trigger a page fault) for a 1 TiB heap with 4 MiB
// arenas which is completely discontiguous. ~160µs is still a lot, but in
// practice most platforms have 64 MiB arenas (which cuts this by a factor
// of 16) and Go heaps are usually mostly contiguous, so the chance that
// an addrRanges even grows to that size is extremely low.
// Because we assume r is not currently represented in a,
// findSucc gives us our insertion index.
i := a.findSucc(r.base.addr())
coalescesDown := i > 0 && a.ranges[i-1].limit.equal(r.base)
coalescesUp := i < len(a.ranges) && r.limit.equal(a.ranges[i].base)
if coalescesUp && coalescesDown {
// We have neighbors and they both border us.
// Merge a.ranges[i-1], r, and a.ranges[i] together into a.ranges[i-1].
a.ranges[i-1].limit = a.ranges[i].limit
// Delete a.ranges[i].
copy(a.ranges[i:], a.ranges[i+1:])
a.ranges = a.ranges[:len(a.ranges)-1]
} else if coalescesDown {
// We have a neighbor at a lower address only and it borders us.
// Merge the new space into a.ranges[i-1].
a.ranges[i-1].limit = r.limit
} else if coalescesUp {
// We have a neighbor at a higher address only and it borders us.
// Merge the new space into a.ranges[i].
a.ranges[i].base = r.base
} else {
// We may or may not have neighbors which don't border us.
// Add the new range.
if len(a.ranges)+1 > cap(a.ranges) {
// Grow the array. Note that this leaks the old array, but since
// we're doubling we have at most 2x waste. For a 1 TiB heap and
// 4 MiB arenas which are all discontiguous (both very conservative
// assumptions), this would waste at most 4 MiB of memory.
oldRanges := a.ranges
ranges := (*notInHeapSlice)(unsafe.Pointer(&a.ranges))
ranges.len = len(oldRanges) + 1
ranges.cap = cap(oldRanges) * 2
ranges.array = (*notInHeap)(persistentalloc(unsafe.Sizeof(addrRange{})*uintptr(ranges.cap), sys.PtrSize, a.sysStat))
// Copy in the old array, but make space for the new range.
copy(a.ranges[:i], oldRanges[:i])
copy(a.ranges[i+1:], oldRanges[i:])
} else {
a.ranges = a.ranges[:len(a.ranges)+1]
copy(a.ranges[i+1:], a.ranges[i:])
a.ranges[i] = r
a.totalBytes += r.size()
// removeLast removes and returns the highest-addressed contiguous range
// of a, or the last nBytes of that range, whichever is smaller. If a is
// empty, it returns an empty range.
func (a *addrRanges) removeLast(nBytes uintptr) addrRange {
if len(a.ranges) == 0 {
return addrRange{}
r := a.ranges[len(a.ranges)-1]
size := r.size()
if size > nBytes {
newEnd := r.limit.sub(nBytes)
a.ranges[len(a.ranges)-1].limit = newEnd
a.totalBytes -= nBytes
return addrRange{newEnd, r.limit}
a.ranges = a.ranges[:len(a.ranges)-1]
a.totalBytes -= size
return r
// removeGreaterEqual removes the ranges of a which are above addr, and additionally
// splits any range containing addr.
func (a *addrRanges) removeGreaterEqual(addr uintptr) {
pivot := a.findSucc(addr)
if pivot == 0 {
// addr is before all ranges in a.
a.totalBytes = 0
a.ranges = a.ranges[:0]
removed := uintptr(0)
for _, r := range a.ranges[pivot:] {
removed += r.size()
if r := a.ranges[pivot-1]; r.contains(addr) {
removed += r.size()
r = r.removeGreaterEqual(addr)
if r.size() == 0 {
} else {
removed -= r.size()
a.ranges[pivot-1] = r
a.ranges = a.ranges[:pivot]
a.totalBytes -= removed
// cloneInto makes a deep clone of a's state into b, re-using
// b's ranges if able.
func (a *addrRanges) cloneInto(b *addrRanges) {
if len(a.ranges) > cap(b.ranges) {
// Grow the array.
ranges := (*notInHeapSlice)(unsafe.Pointer(&b.ranges))
ranges.len = 0
ranges.cap = cap(a.ranges)
ranges.array = (*notInHeap)(persistentalloc(unsafe.Sizeof(addrRange{})*uintptr(ranges.cap), sys.PtrSize, b.sysStat))
b.ranges = b.ranges[:len(a.ranges)]
b.totalBytes = a.totalBytes
copy(b.ranges, a.ranges)