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// Copyright 2022 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.
#ifndef V8_HEAP_BASE_ACTIVE_SYSTEM_PAGES_H_
#define V8_HEAP_BASE_ACTIVE_SYSTEM_PAGES_H_
#include <bitset>
#include <cstdint>
#include "src/base/macros.h"
namespace heap {
namespace base {
// Class implements a bitset of system pages on a heap page.
class ActiveSystemPages final {
public:
// Defines the maximum number of system pages that can be tracked in one
// instance.
static constexpr size_t kMaxPages = 64;
// Initializes the set of active pages to the system pages for the header.
V8_EXPORT_PRIVATE size_t Init(size_t header_size, size_t page_size_bits,
size_t user_page_size);
// Adds the pages for this memory range. Returns the number of freshly added
// pages.
V8_EXPORT_PRIVATE size_t Add(size_t start, size_t end, size_t page_size_bits);
// Replaces the current bitset with the given argument. The new bitset needs
// to be a proper subset of the current pages, which means this operation
// can't add pages. Returns the number of removed pages.
V8_EXPORT_PRIVATE size_t Reduce(ActiveSystemPages updated_value);
// Removes all pages. Returns the number of removed pages.
V8_EXPORT_PRIVATE size_t Clear();
// Returns the memory used with the given page size.
V8_EXPORT_PRIVATE size_t Size(size_t page_size_bits) const;
private:
using bitset_t = std::bitset<kMaxPages>;
bitset_t value_;
};
} // namespace base
} // namespace heap
#endif // V8_HEAP_BASE_ACTIVE_SYSTEM_PAGES_H_
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