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// Copyright 2018 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <set>
#include "src/base/address-region.h"
#include "src/base/utils/random-number-generator.h"
namespace v8 {
namespace base {
// Helper class for managing used/free regions within [address, address+size)
// region. Minimum allocation unit is |page_size|. Requested allocation size
// is rounded up to |page_size|.
// The region allocation algorithm implements best-fit with coalescing strategy:
// it tries to find a smallest suitable free region upon allocation and tries
// to merge region with its neighbors upon freeing.
// This class does not perform any actual region reservation.
// Not thread-safe.
class V8_BASE_EXPORT RegionAllocator final {
using Address = uintptr_t;
static constexpr Address kAllocationFailure = static_cast<Address>(-1);
RegionAllocator(Address address, size_t size, size_t page_size);
// Allocates region of |size| (must be |page_size|-aligned). Returns
// the address of the region on success or kAllocationFailure.
Address AllocateRegion(size_t size);
// Same as above but tries to randomize the region displacement.
Address AllocateRegion(RandomNumberGenerator* rng, size_t size);
// Allocates region of |size| at |requested_address| if it's free. Both the
// address and the size must be |page_size|-aligned. On success returns
// true.
// This kind of allocation is supposed to be used during setup phase to mark
// certain regions as used or for randomizing regions displacement.
bool AllocateRegionAt(Address requested_address, size_t size);
// Frees region at given |address|, returns the size of the region.
// There must be a used region starting at given address otherwise nothing
// will be freed and 0 will be returned.
size_t FreeRegion(Address address) { return TrimRegion(address, 0); }
// Decreases size of the previously allocated region at |address|, returns
// freed size. |new_size| must be |page_size|-aligned and
// less than or equal to current region's size. Setting new size to zero
// frees the region.
size_t TrimRegion(Address address, size_t new_size);
// If there is a used region starting at given address returns its size
// otherwise 0.
size_t CheckRegion(Address address);
// Returns true if there are no pages allocated in given region.
bool IsFree(Address address, size_t size);
Address begin() const { return whole_region_.begin(); }
Address end() const { return whole_region_.end(); }
size_t size() const { return whole_region_.size(); }
bool contains(Address address) const {
return whole_region_.contains(address);
bool contains(Address address, size_t size) const {
return whole_region_.contains(address, size);
// Total size of not yet aquired regions.
size_t free_size() const { return free_size_; }
// The alignment of the allocated region's addresses and granularity of
// the allocated region's sizes.
size_t page_size() const { return page_size_; }
void Print(std::ostream& os) const;
class Region : public AddressRegion {
Region(Address address, size_t size, bool is_used)
: AddressRegion(address, size), is_used_(is_used) {}
bool is_used() const { return is_used_; }
void set_is_used(bool used) { is_used_ = used; }
void Print(std::ostream& os) const;
bool is_used_;
// The whole region.
const Region whole_region_;
// Number of |page_size_| in the whole region.
const size_t region_size_in_pages_;
// If the free size is less than this value - stop trying to randomize the
// allocation addresses.
const size_t max_load_for_randomization_;
// Size of all free regions.
size_t free_size_;
// Minimum region size. Must be a pow of 2.
const size_t page_size_;
struct AddressEndOrder {
bool operator()(const Region* a, const Region* b) const {
return a->end() < b->end();
// All regions ordered by addresses.
using AllRegionsSet = std::set<Region*, AddressEndOrder>;
AllRegionsSet all_regions_;
struct SizeAddressOrder {
bool operator()(const Region* a, const Region* b) const {
if (a->size() != b->size()) return a->size() < b->size();
return a->begin() < b->begin();
// Free regions ordered by sizes and addresses.
std::set<Region*, SizeAddressOrder> free_regions_;
// Returns region containing given address or nullptr.
AllRegionsSet::iterator FindRegion(Address address);
// Adds given region to the set of free regions.
void FreeListAddRegion(Region* region);
// Finds best-fit free region for given size.
Region* FreeListFindRegion(size_t size);
// Removes given region from the set of free regions.
void FreeListRemoveRegion(Region* region);
// Splits given |region| into two: one of |new_size| size and a new one
// having the rest. The new region is returned.
Region* Split(Region* region, size_t new_size);
// For two coalescing regions merges |next| to |prev| and deletes |next|.
void Merge(AllRegionsSet::iterator prev_iter,
AllRegionsSet::iterator next_iter);
} // namespace base
} // namespace v8