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// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
// Copyright (c) 2005, Google Inc.
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//
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// ---
// Author: Sanjay Ghemawat <opensource@google.com>
//
// A data structure used by the caching malloc. It maps from page# to
// a pointer that contains info about that page. We use two
// representations: one for 32-bit addresses, and another for 64 bit
// addresses. Both representations provide the same interface. The
// first representation is implemented as a flat array, the seconds as
// a three-level radix tree that strips away approximately 1/3rd of
// the bits every time.
//
// The BITS parameter should be the number of bits required to hold
// a page number. E.g., with 32 bit pointers and 4K pages (i.e.,
// page offset fits in lower 12 bits), BITS == 20.
#ifndef TCMALLOC_PAGEMAP_H_
#define TCMALLOC_PAGEMAP_H_
#include "config.h"
#include <stddef.h> // for NULL, size_t
#include <string.h> // for memset
#if defined HAVE_STDINT_H
#include <stdint.h>
#elif defined HAVE_INTTYPES_H
#include <inttypes.h>
#else
#include <sys/types.h>
#endif
#include "internal_logging.h" // for ASSERT
// Single-level array
template <int BITS>
class TCMalloc_PageMap1 {
private:
static const int LENGTH = 1 << BITS;
void** array_;
public:
typedef uintptr_t Number;
explicit TCMalloc_PageMap1(void* (*allocator)(size_t)) {
array_ = reinterpret_cast<void**>((*allocator)(sizeof(void*) << BITS));
memset(array_, 0, sizeof(void*) << BITS);
}
// Ensure that the map contains initialized entries "x .. x+n-1".
// Returns true if successful, false if we could not allocate memory.
bool Ensure(Number x, size_t n) {
// Nothing to do since flat array was allocated at start. All
// that's left is to check for overflow (that is, we don't want to
// ensure a number y where array_[y] would be an out-of-bounds
// access).
return n <= LENGTH - x; // an overflow-free way to do "x + n <= LENGTH"
}
void PreallocateMoreMemory() {}
// Return the current value for KEY. Returns NULL if not yet set,
// or if k is out of range.
void* get(Number k) const {
if ((k >> BITS) > 0) {
return NULL;
}
return array_[k];
}
// REQUIRES "k" is in range "[0,2^BITS-1]".
// REQUIRES "k" has been ensured before.
//
// Sets the value 'v' for key 'k'.
void set(Number k, void* v) {
array_[k] = v;
}
// Return the first non-NULL pointer found in this map for
// a page number >= k. Returns NULL if no such number is found.
void* Next(Number k) const {
while (k < (1 << BITS)) {
if (array_[k] != NULL) return array_[k];
k++;
}
return NULL;
}
};
// Two-level radix tree
template <int BITS>
class TCMalloc_PageMap2 {
private:
// Put 32 entries in the root and (2^BITS)/32 entries in each leaf.
static const int ROOT_BITS = 5;
static const int ROOT_LENGTH = 1 << ROOT_BITS;
static const int LEAF_BITS = BITS - ROOT_BITS;
static const int LEAF_LENGTH = 1 << LEAF_BITS;
// Leaf node
struct Leaf {
void* values[LEAF_LENGTH];
};
Leaf* root_[ROOT_LENGTH]; // Pointers to 32 child nodes
void* (*allocator_)(size_t); // Memory allocator
public:
typedef uintptr_t Number;
explicit TCMalloc_PageMap2(void* (*allocator)(size_t)) {
allocator_ = allocator;
memset(root_, 0, sizeof(root_));
}
void* get(Number k) const {
const Number i1 = k >> LEAF_BITS;
const Number i2 = k & (LEAF_LENGTH-1);
if ((k >> BITS) > 0 || root_[i1] == NULL) {
return NULL;
}
return root_[i1]->values[i2];
}
void set(Number k, void* v) {
const Number i1 = k >> LEAF_BITS;
const Number i2 = k & (LEAF_LENGTH-1);
ASSERT(i1 < ROOT_LENGTH);
root_[i1]->values[i2] = v;
}
bool Ensure(Number start, size_t n) {
for (Number key = start; key <= start + n - 1; ) {
const Number i1 = key >> LEAF_BITS;
// Check for overflow
if (i1 >= ROOT_LENGTH)
return false;
// Make 2nd level node if necessary
if (root_[i1] == NULL) {
Leaf* leaf = reinterpret_cast<Leaf*>((*allocator_)(sizeof(Leaf)));
if (leaf == NULL) return false;
memset(leaf, 0, sizeof(*leaf));
root_[i1] = leaf;
}
// Advance key past whatever is covered by this leaf node
key = ((key >> LEAF_BITS) + 1) << LEAF_BITS;
}
return true;
}
void PreallocateMoreMemory() {
// Allocate enough to keep track of all possible pages
Ensure(0, 1 << BITS);
}
void* Next(Number k) const {
while (k < (1 << BITS)) {
const Number i1 = k >> LEAF_BITS;
Leaf* leaf = root_[i1];
if (leaf != NULL) {
// Scan forward in leaf
for (Number i2 = k & (LEAF_LENGTH - 1); i2 < LEAF_LENGTH; i2++) {
if (leaf->values[i2] != NULL) {
return leaf->values[i2];
}
}
}
// Skip to next top-level entry
k = (i1 + 1) << LEAF_BITS;
}
return NULL;
}
};
// Three-level radix tree
template <int BITS>
class TCMalloc_PageMap3 {
private:
// How many bits should we consume at each interior level
static const int INTERIOR_BITS = (BITS + 2) / 3; // Round-up
static const int INTERIOR_LENGTH = 1 << INTERIOR_BITS;
// How many bits should we consume at leaf level
static const int LEAF_BITS = BITS - 2*INTERIOR_BITS;
static const int LEAF_LENGTH = 1 << LEAF_BITS;
// Interior node
struct Node {
Node* ptrs[INTERIOR_LENGTH];
};
// Leaf node
struct Leaf {
void* values[LEAF_LENGTH];
};
Node* root_; // Root of radix tree
void* (*allocator_)(size_t); // Memory allocator
Node* NewNode() {
Node* result = reinterpret_cast<Node*>((*allocator_)(sizeof(Node)));
if (result != NULL) {
memset(result, 0, sizeof(*result));
}
return result;
}
public:
typedef uintptr_t Number;
explicit TCMalloc_PageMap3(void* (*allocator)(size_t)) {
allocator_ = allocator;
root_ = NewNode();
}
void* get(Number k) const {
const Number i1 = k >> (LEAF_BITS + INTERIOR_BITS);
const Number i2 = (k >> LEAF_BITS) & (INTERIOR_LENGTH-1);
const Number i3 = k & (LEAF_LENGTH-1);
if ((k >> BITS) > 0 ||
root_->ptrs[i1] == NULL || root_->ptrs[i1]->ptrs[i2] == NULL) {
return NULL;
}
return reinterpret_cast<Leaf*>(root_->ptrs[i1]->ptrs[i2])->values[i3];
}
void set(Number k, void* v) {
ASSERT(k >> BITS == 0);
const Number i1 = k >> (LEAF_BITS + INTERIOR_BITS);
const Number i2 = (k >> LEAF_BITS) & (INTERIOR_LENGTH-1);
const Number i3 = k & (LEAF_LENGTH-1);
reinterpret_cast<Leaf*>(root_->ptrs[i1]->ptrs[i2])->values[i3] = v;
}
bool Ensure(Number start, size_t n) {
for (Number key = start; key <= start + n - 1; ) {
const Number i1 = key >> (LEAF_BITS + INTERIOR_BITS);
const Number i2 = (key >> LEAF_BITS) & (INTERIOR_LENGTH-1);
// Check for overflow
if (i1 >= INTERIOR_LENGTH || i2 >= INTERIOR_LENGTH)
return false;
// Make 2nd level node if necessary
if (root_->ptrs[i1] == NULL) {
Node* n = NewNode();
if (n == NULL) return false;
root_->ptrs[i1] = n;
}
// Make leaf node if necessary
if (root_->ptrs[i1]->ptrs[i2] == NULL) {
Leaf* leaf = reinterpret_cast<Leaf*>((*allocator_)(sizeof(Leaf)));
if (leaf == NULL) return false;
memset(leaf, 0, sizeof(*leaf));
root_->ptrs[i1]->ptrs[i2] = reinterpret_cast<Node*>(leaf);
}
// Advance key past whatever is covered by this leaf node
key = ((key >> LEAF_BITS) + 1) << LEAF_BITS;
}
return true;
}
void PreallocateMoreMemory() {
}
void* Next(Number k) const {
while (k < (Number(1) << BITS)) {
const Number i1 = k >> (LEAF_BITS + INTERIOR_BITS);
const Number i2 = (k >> LEAF_BITS) & (INTERIOR_LENGTH-1);
if (root_->ptrs[i1] == NULL) {
// Advance to next top-level entry
k = (i1 + 1) << (LEAF_BITS + INTERIOR_BITS);
} else {
Leaf* leaf = reinterpret_cast<Leaf*>(root_->ptrs[i1]->ptrs[i2]);
if (leaf != NULL) {
for (Number i3 = (k & (LEAF_LENGTH-1)); i3 < LEAF_LENGTH; i3++) {
if (leaf->values[i3] != NULL) {
return leaf->values[i3];
}
}
}
// Advance to next interior entry
k = ((k >> LEAF_BITS) + 1) << LEAF_BITS;
}
}
return NULL;
}
};
#endif // TCMALLOC_PAGEMAP_H_