Source File
mpallocbits.go
Belonging Package
runtime
// 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.
package runtime
import (
)
// pageBits is a bitmap representing one bit per page in a palloc chunk.
type pageBits [pallocChunkPages / 64]uint64
// get returns the value of the i'th bit in the bitmap.
func ( *pageBits) ( uint) uint {
return uint(([/64] >> ( % 64)) & 1)
}
// block64 returns the 64-bit aligned block of bits containing the i'th bit.
func ( *pageBits) ( uint) uint64 {
return [/64]
}
// set sets bit i of pageBits.
func ( *pageBits) ( uint) {
[/64] |= 1 << ( % 64)
}
// setRange sets bits in the range [i, i+n).
func ( *pageBits) (, uint) {
_ = [/64]
if == 1 {
// Fast path for the n == 1 case.
.set()
return
}
// Set bits [i, j].
:= + - 1
if /64 == /64 {
[/64] |= ((uint64(1) << ) - 1) << ( % 64)
return
}
_ = [/64]
// Set leading bits.
[/64] |= ^uint64(0) << ( % 64)
for := /64 + 1; < /64; ++ {
[] = ^uint64(0)
}
// Set trailing bits.
[/64] |= (uint64(1) << (%64 + 1)) - 1
}
// setAll sets all the bits of b.
func ( *pageBits) () {
for := range {
[] = ^uint64(0)
}
}
// setBlock64 sets the 64-bit aligned block of bits containing the i'th bit that
// are set in v.
func ( *pageBits) ( uint, uint64) {
[/64] |=
}
// clear clears bit i of pageBits.
func ( *pageBits) ( uint) {
[/64] &^= 1 << ( % 64)
}
// clearRange clears bits in the range [i, i+n).
func ( *pageBits) (, uint) {
_ = [/64]
if == 1 {
// Fast path for the n == 1 case.
.clear()
return
}
// Clear bits [i, j].
:= + - 1
if /64 == /64 {
[/64] &^= ((uint64(1) << ) - 1) << ( % 64)
return
}
_ = [/64]
// Clear leading bits.
[/64] &^= ^uint64(0) << ( % 64)
clear([/64+1 : /64])
// Clear trailing bits.
[/64] &^= (uint64(1) << (%64 + 1)) - 1
}
// clearAll frees all the bits of b.
func ( *pageBits) () {
clear([:])
}
// clearBlock64 clears the 64-bit aligned block of bits containing the i'th bit that
// are set in v.
func ( *pageBits) ( uint, uint64) {
[/64] &^=
}
// popcntRange counts the number of set bits in the
// range [i, i+n).
func ( *pageBits) (, uint) ( uint) {
if == 1 {
return uint(([/64] >> ( % 64)) & 1)
}
_ = [/64]
:= + - 1
if /64 == /64 {
return uint(sys.OnesCount64(([/64] >> ( % 64)) & ((1 << ) - 1)))
}
_ = [/64]
+= uint(sys.OnesCount64([/64] >> ( % 64)))
for := /64 + 1; < /64; ++ {
+= uint(sys.OnesCount64([]))
}
+= uint(sys.OnesCount64([/64] & ((1 << (%64 + 1)) - 1)))
return
}
// pallocBits is a bitmap that tracks page allocations for at most one
// palloc chunk.
//
// The precise representation is an implementation detail, but for the
// sake of documentation, 0s are free pages and 1s are allocated pages.
type pallocBits pageBits
// summarize returns a packed summary of the bitmap in pallocBits.
func ( *pallocBits) () pallocSum {
var , , uint
const = ^uint(0) // sentinel for start value
=
for := 0; < len(); ++ {
:= []
if == 0 {
+= 64
continue
}
:= uint(sys.TrailingZeros64())
:= uint(sys.LeadingZeros64())
// Finish any region spanning the uint64s
+=
if == {
=
}
= max(, )
// Final region that might span to next uint64
=
}
if == {
// Made it all the way through without finding a single 1 bit.
const = uint(64 * len())
return packPallocSum(, , )
}
= max(, )
if >= 64-2 {
// There is no way an internal run of zeros could beat max.
return packPallocSum(, , )
}
// Now look inside each uint64 for runs of zeros.
// All uint64s must be nonzero, or we would have aborted above.
:
for := 0; < len(); ++ {
:= []
// Look inside this uint64. We have a pattern like
// 000000 1xxxxx1 000000
// We need to look inside the 1xxxxx1 for any contiguous
// region of zeros.
// We already know the trailing zeros are no larger than max. Remove them.
>>= sys.TrailingZeros64() & 63
if &(+1) == 0 { // no more zeros (except at the top).
continue
}
// Strategy: shrink all runs of zeros by max. If any runs of zero
// remain, then we've identified a larger maximum zero run.
:= // number of zeros we still need to shrink by.
:= uint(1) // current minimum length of runs of ones in x.
for {
// Shrink all runs of zeros by p places (except the top zeros).
for > 0 {
if <= {
// Shift p ones down into the top of each run of zeros.
|= >> ( & 63)
if &(+1) == 0 { // no more zeros (except at the top).
continue
}
break
}
// Shift k ones down into the top of each run of zeros.
|= >> ( & 63)
if &(+1) == 0 { // no more zeros (except at the top).
continue
}
-=
// We've just doubled the minimum length of 1-runs.
// This allows us to shift farther in the next iteration.
*= 2
}
// The length of the lowest-order zero run is an increment to our maximum.
:= uint(sys.TrailingZeros64(^)) // count contiguous trailing ones
>>= & 63 // remove trailing ones
= uint(sys.TrailingZeros64()) // count contiguous trailing zeros
>>= & 63 // remove zeros
+= // we have a new maximum!
if &(+1) == 0 { // no more zeros (except at the top).
continue
}
= // remove j more zeros from each zero run.
}
}
return packPallocSum(, , )
}
// find searches for npages contiguous free pages in pallocBits and returns
// the index where that run starts, as well as the index of the first free page
// it found in the search. searchIdx represents the first known free page and
// where to begin the next search from.
//
// If find fails to find any free space, it returns an index of ^uint(0) and
// the new searchIdx should be ignored.
//
// Note that if npages == 1, the two returned values will always be identical.
func ( *pallocBits) ( uintptr, uint) (uint, uint) {
if == 1 {
:= .find1()
return ,
} else if <= 64 {
return .findSmallN(, )
}
return .findLargeN(, )
}
// find1 is a helper for find which searches for a single free page
// in the pallocBits and returns the index.
//
// See find for an explanation of the searchIdx parameter.
func ( *pallocBits) ( uint) uint {
_ = [0] // lift nil check out of loop
for := / 64; < uint(len()); ++ {
:= []
if ^ == 0 {
continue
}
return *64 + uint(sys.TrailingZeros64(^))
}
return ^uint(0)
}
// findSmallN is a helper for find which searches for npages contiguous free pages
// in this pallocBits and returns the index where that run of contiguous pages
// starts as well as the index of the first free page it finds in its search.
//
// See find for an explanation of the searchIdx parameter.
//
// Returns a ^uint(0) index on failure and the new searchIdx should be ignored.
//
// findSmallN assumes npages <= 64, where any such contiguous run of pages
// crosses at most one aligned 64-bit boundary in the bits.
func ( *pallocBits) ( uintptr, uint) (uint, uint) {
, := uint(0), ^uint(0)
for := / 64; < uint(len()); ++ {
:= []
if ^ == 0 {
= 0
continue
}
// First see if we can pack our allocation in the trailing
// zeros plus the end of the last 64 bits.
if == ^uint(0) {
// The new searchIdx is going to be at these 64 bits after any
// 1s we file, so count trailing 1s.
= *64 + uint(sys.TrailingZeros64(^))
}
:= uint(sys.TrailingZeros64())
if + >= uint() {
return *64 - ,
}
// Next, check the interior of the 64-bit chunk.
:= findBitRange64(^, uint())
if < 64 {
return *64 + ,
}
= uint(sys.LeadingZeros64())
}
return ^uint(0),
}
// findLargeN is a helper for find which searches for npages contiguous free pages
// in this pallocBits and returns the index where that run starts, as well as the
// index of the first free page it found it its search.
//
// See alloc for an explanation of the searchIdx parameter.
//
// Returns a ^uint(0) index on failure and the new searchIdx should be ignored.
//
// findLargeN assumes npages > 64, where any such run of free pages
// crosses at least one aligned 64-bit boundary in the bits.
func ( *pallocBits) ( uintptr, uint) (uint, uint) {
, , := ^uint(0), uint(0), ^uint(0)
for := / 64; < uint(len()); ++ {
:= []
if == ^uint64(0) {
= 0
continue
}
if == ^uint(0) {
// The new searchIdx is going to be at these 64 bits after any
// 1s we file, so count trailing 1s.
= *64 + uint(sys.TrailingZeros64(^))
}
if == 0 {
= uint(sys.LeadingZeros64())
= *64 + 64 -
continue
}
:= uint(sys.TrailingZeros64())
if + >= uint() {
return ,
}
if < 64 {
= uint(sys.LeadingZeros64())
= *64 + 64 -
continue
}
+= 64
}
if < uint() {
return ^uint(0),
}
return ,
}
// allocRange allocates the range [i, i+n).
func ( *pallocBits) (, uint) {
(*pageBits)().setRange(, )
}
// allocAll allocates all the bits of b.
func ( *pallocBits) () {
(*pageBits)().setAll()
}
// free1 frees a single page in the pallocBits at i.
func ( *pallocBits) ( uint) {
(*pageBits)().clear()
}
// free frees the range [i, i+n) of pages in the pallocBits.
func ( *pallocBits) (, uint) {
(*pageBits)().clearRange(, )
}
// freeAll frees all the bits of b.
func ( *pallocBits) () {
(*pageBits)().clearAll()
}
// pages64 returns a 64-bit bitmap representing a block of 64 pages aligned
// to 64 pages. The returned block of pages is the one containing the i'th
// page in this pallocBits. Each bit represents whether the page is in-use.
func ( *pallocBits) ( uint) uint64 {
return (*pageBits)().block64()
}
// allocPages64 allocates a 64-bit block of 64 pages aligned to 64 pages according
// to the bits set in alloc. The block set is the one containing the i'th page.
func ( *pallocBits) ( uint, uint64) {
(*pageBits)().setBlock64(, )
}
// findBitRange64 returns the bit index of the first set of
// n consecutive 1 bits. If no consecutive set of 1 bits of
// size n may be found in c, then it returns an integer >= 64.
// n must be > 0.
func findBitRange64( uint64, uint) uint {
// This implementation is based on shrinking the length of
// runs of contiguous 1 bits. We remove the top n-1 1 bits
// from each run of 1s, then look for the first remaining 1 bit.
:= - 1 // number of 1s we want to remove.
:= uint(1) // current minimum width of runs of 0 in c.
for > 0 {
if <= {
// Shift p 0s down into the top of each run of 1s.
&= >> ( & 63)
break
}
// Shift k 0s down into the top of each run of 1s.
&= >> ( & 63)
if == 0 {
return 64
}
-=
// We've just doubled the minimum length of 0-runs.
// This allows us to shift farther in the next iteration.
*= 2
}
// Find first remaining 1.
// Since we shrunk from the top down, the first 1 is in
// its correct original position.
return uint(sys.TrailingZeros64())
}
// pallocData encapsulates pallocBits and a bitmap for
// whether or not a given page is scavenged in a single
// structure. It's effectively a pallocBits with
// additional functionality.
//
// Update the comment on (*pageAlloc).chunks should this
// structure change.
type pallocData struct {
pallocBits
scavenged pageBits
}
// allocRange sets bits [i, i+n) in the bitmap to 1 and
// updates the scavenged bits appropriately.
func ( *pallocData) (, uint) {
// Clear the scavenged bits when we alloc the range.
.pallocBits.allocRange(, )
.scavenged.clearRange(, )
}
// allocAll sets every bit in the bitmap to 1 and updates
// the scavenged bits appropriately.
func ( *pallocData) () {
// Clear the scavenged bits when we alloc the range.
.pallocBits.allocAll()
.scavenged.clearAll()
}
The pages are generated with Golds v0.6.9-preview. (GOOS=linux GOARCH=amd64) Golds is a Go 101 project developed by Tapir Liu. PR and bug reports are welcome and can be submitted to the issue list. Please follow @Go100and1 (reachable from the left QR code) to get the latest news of Golds. |