1 files changed, 436 insertions, 0 deletions
diff --git a/src/runtime/mranges.go b/src/runtime/mranges.go
new file mode 100644
index 0000000..9cf83cc
--- /dev/null
+++ b/src/runtime/mranges.go
@@ -0,0 +1,436 @@
+// 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 (
+	"internal/goarch"
+	"runtime/internal/atomic"
+	"unsafe"
+)
+
+// 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
+}
+
+// atomicOffAddr is like offAddr, but operations on it are atomic.
+// It also contains operations to be able to store marked addresses
+// to ensure that they're not overridden until they've been seen.
+type atomicOffAddr struct {
+	// a contains the offset address, unlike offAddr.
+	a atomic.Int64
+}
+
+// Clear attempts to store minOffAddr in atomicOffAddr. It may fail
+// if a marked value is placed in the box in the meanwhile.
+func (b *atomicOffAddr) Clear() {
+	for {
+		old := b.a.Load()
+		if old < 0 {
+			return
+		}
+		if b.a.CompareAndSwap(old, int64(minOffAddr.addr()-arenaBaseOffset)) {
+			return
+		}
+	}
+}
+
+// StoreMin stores addr if it's less than the current value in the
+// offset address space if the current value is not marked.
+func (b *atomicOffAddr) StoreMin(addr uintptr) {
+	new := int64(addr - arenaBaseOffset)
+	for {
+		old := b.a.Load()
+		if old < new {
+			return
+		}
+		if b.a.CompareAndSwap(old, new) {
+			return
+		}
+	}
+}
+
+// StoreUnmark attempts to unmark the value in atomicOffAddr and
+// replace it with newAddr. markedAddr must be a marked address
+// returned by Load. This function will not store newAddr if the
+// box no longer contains markedAddr.
+func (b *atomicOffAddr) StoreUnmark(markedAddr, newAddr uintptr) {
+	b.a.CompareAndSwap(-int64(markedAddr-arenaBaseOffset), int64(newAddr-arenaBaseOffset))
+}
+
+// StoreMarked stores addr but first converted to the offset address
+// space and then negated.
+func (b *atomicOffAddr) StoreMarked(addr uintptr) {
+	b.a.Store(-int64(addr - arenaBaseOffset))
+}
+
+// Load returns the address in the box as a virtual address. It also
+// returns if the value was marked or not.
+func (b *atomicOffAddr) Load() (uintptr, bool) {
+	v := b.a.Load()
+	wasMarked := false
+	if v < 0 {
+		wasMarked = true
+		v = -v
+	}
+	return uintptr(v) + arenaBaseOffset, wasMarked
+}
+
+// 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 *sysMemStat
+}
+
+func (a *addrRanges) init(sysStat *sysMemStat) {
+	ranges := (*notInHeapSlice)(unsafe.Pointer(&a.ranges))
+	ranges.len = 0
+	ranges.cap = 16
+	ranges.array = (*notInHeap)(persistentalloc(unsafe.Sizeof(addrRange{})*uintptr(ranges.cap), goarch.PtrSize, sysStat))
+	a.sysStat = sysStat
+	a.totalBytes = 0
+}
+
+// findSucc returns the first index in a such that addr is
+// less than the base of the addrRange at that index.
+func (a *addrRanges) findSucc(addr uintptr) int {
+	base := offAddr{addr}
+
+	// Narrow down the search space via a binary search
+	// for large addrRanges until we have at most iterMax
+	// candidates left.
+	const iterMax = 8
+	bot, top := 0, len(a.ranges)
+	for top-bot > iterMax {
+		i := ((top - bot) / 2) + bot
+		if a.ranges[i].contains(base.addr()) {
+			// a.ranges[i] contains base, so
+			// its successor is the next index.
+			return i + 1
+		}
+		if base.lessThan(a.ranges[i].base) {
+			// In this case i might actually be
+			// the successor, but we can't be sure
+			// until we check the ones before it.
+			top = i
+		} else {
+			// In this case we know base is
+			// greater than or equal to a.ranges[i].limit-1,
+			// so i is definitely not the successor.
+			// We already checked i, so pick the next
+			// one.
+			bot = i + 1
+		}
+	}
+	// There are top-bot candidates left, so
+	// iterate over them and find the first that
+	// base is strictly less than.
+	for i := bot; i < top; i++ {
+		if base.lessThan(a.ranges[i].base) {
+			return i
+		}
+	}
+	return top
+}
+
+// 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 and r.size() must be > 0.
+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.
+
+	// An empty range has no effect on the set of addresses represented
+	// by a, but passing a zero-sized range is almost always a bug.
+	if r.size() == 0 {
+		print("runtime: range = {", hex(r.base.addr()), ", ", hex(r.limit.addr()), "}\n")
+		throw("attempted to add zero-sized address range")
+	}
+	// 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), goarch.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]
+		return
+	}
+	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 {
+			pivot--
+		} 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), goarch.PtrSize, b.sysStat))
+	}
+	b.ranges = b.ranges[:len(a.ranges)]
+	b.totalBytes = a.totalBytes
+	copy(b.ranges, a.ranges)
+}