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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.
// +build amd64 !ios,arm64 mips64 mips64le ppc64 ppc64le riscv64 s390x
// See mpagealloc_32bit.go for why ios/arm64 is excluded here.
package runtime
import "unsafe"
const (
// The number of levels in the radix tree.
summaryLevels = 5
// Constants for testing.
pageAlloc32Bit = 0
pageAlloc64Bit = 1
// Number of bits needed to represent all indices into the L1 of the
// chunks map.
// See (*pageAlloc).chunks for more details. Update the documentation
// there should this number change.
pallocChunksL1Bits = 13
// levelBits is the number of bits in the radix for a given level in the super summary
// structure.
// The sum of all the entries of levelBits should equal heapAddrBits.
var levelBits = [summaryLevels]uint{
// levelShift is the number of bits to shift to acquire the radix for a given level
// in the super summary structure.
// With levelShift, one can compute the index of the summary at level l related to a
// pointer p by doing:
// p >> levelShift[l]
var levelShift = [summaryLevels]uint{
heapAddrBits - summaryL0Bits,
heapAddrBits - summaryL0Bits - 1*summaryLevelBits,
heapAddrBits - summaryL0Bits - 2*summaryLevelBits,
heapAddrBits - summaryL0Bits - 3*summaryLevelBits,
heapAddrBits - summaryL0Bits - 4*summaryLevelBits,
// levelLogPages is log2 the maximum number of runtime pages in the address space
// a summary in the given level represents.
// The leaf level always represents exactly log2 of 1 chunk's worth of pages.
var levelLogPages = [summaryLevels]uint{
logPallocChunkPages + 4*summaryLevelBits,
logPallocChunkPages + 3*summaryLevelBits,
logPallocChunkPages + 2*summaryLevelBits,
logPallocChunkPages + 1*summaryLevelBits,
// sysInit performs architecture-dependent initialization of fields
// in pageAlloc. pageAlloc should be uninitialized except for sysStat
// if any runtime statistic should be updated.
func (p *pageAlloc) sysInit() {
// Reserve memory for each level. This will get mapped in
// as R/W by setArenas.
for l, shift := range levelShift {
entries := 1 << (heapAddrBits - shift)
// Reserve b bytes of memory anywhere in the address space.
b := alignUp(uintptr(entries)*pallocSumBytes, physPageSize)
r := sysReserve(nil, b)
if r == nil {
throw("failed to reserve page summary memory")
// Put this reservation into a slice.
sl := notInHeapSlice{(*notInHeap)(r), 0, entries}
p.summary[l] = *(*[]pallocSum)(unsafe.Pointer(&sl))
// sysGrow performs architecture-dependent operations on heap
// growth for the page allocator, such as mapping in new memory
// for summaries. It also updates the length of the slices in
// [.summary.
// base is the base of the newly-added heap memory and limit is
// the first address past the end of the newly-added heap memory.
// Both must be aligned to pallocChunkBytes.
// The caller must update p.start and p.end after calling sysGrow.
func (p *pageAlloc) sysGrow(base, limit uintptr) {
if base%pallocChunkBytes != 0 || limit%pallocChunkBytes != 0 {
print("runtime: base = ", hex(base), ", limit = ", hex(limit), "\n")
throw("sysGrow bounds not aligned to pallocChunkBytes")
// addrRangeToSummaryRange converts a range of addresses into a range
// of summary indices which must be mapped to support those addresses
// in the summary range.
addrRangeToSummaryRange := func(level int, r addrRange) (int, int) {
sumIdxBase, sumIdxLimit := addrsToSummaryRange(level, r.base.addr(), r.limit.addr())
return blockAlignSummaryRange(level, sumIdxBase, sumIdxLimit)
// summaryRangeToSumAddrRange converts a range of indices in any
// level of p.summary into page-aligned addresses which cover that
// range of indices.
summaryRangeToSumAddrRange := func(level, sumIdxBase, sumIdxLimit int) addrRange {
baseOffset := alignDown(uintptr(sumIdxBase)*pallocSumBytes, physPageSize)
limitOffset := alignUp(uintptr(sumIdxLimit)*pallocSumBytes, physPageSize)
base := unsafe.Pointer(&p.summary[level][0])
return addrRange{
offAddr{uintptr(add(base, baseOffset))},
offAddr{uintptr(add(base, limitOffset))},
// addrRangeToSumAddrRange is a convienience function that converts
// an address range r to the address range of the given summary level
// that stores the summaries for r.
addrRangeToSumAddrRange := func(level int, r addrRange) addrRange {
sumIdxBase, sumIdxLimit := addrRangeToSummaryRange(level, r)
return summaryRangeToSumAddrRange(level, sumIdxBase, sumIdxLimit)
// Find the first inUse index which is strictly greater than base.
// Because this function will never be asked remap the same memory
// twice, this index is effectively the index at which we would insert
// this new growth, and base will never overlap/be contained within
// any existing range.
// This will be used to look at what memory in the summary array is already
// mapped before and after this new range.
inUseIndex := p.inUse.findSucc(base)
// Walk up the radix tree and map summaries in as needed.
for l := range p.summary {
// Figure out what part of the summary array this new address space needs.
needIdxBase, needIdxLimit := addrRangeToSummaryRange(l, makeAddrRange(base, limit))
// Update the summary slices with a new upper-bound. This ensures
// we get tight bounds checks on at least the top bound.
// We must do this regardless of whether we map new memory.
if needIdxLimit > len(p.summary[l]) {
p.summary[l] = p.summary[l][:needIdxLimit]
// Compute the needed address range in the summary array for level l.
need := summaryRangeToSumAddrRange(l, needIdxBase, needIdxLimit)
// Prune need down to what needs to be newly mapped. Some parts of it may
// already be mapped by what inUse describes due to page alignment requirements
// for mapping. prune's invariants are guaranteed by the fact that this
// function will never be asked to remap the same memory twice.
if inUseIndex > 0 {
need = need.subtract(addrRangeToSumAddrRange(l, p.inUse.ranges[inUseIndex-1]))
if inUseIndex < len(p.inUse.ranges) {
need = need.subtract(addrRangeToSumAddrRange(l, p.inUse.ranges[inUseIndex]))
// It's possible that after our pruning above, there's nothing new to map.
if need.size() == 0 {
// Map and commit need.
sysMap(unsafe.Pointer(need.base.addr()), need.size(), p.sysStat)
sysUsed(unsafe.Pointer(need.base.addr()), need.size())