serenity/Kernel/VM/AnonymousVMObject.h

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <Kernel/PhysicalAddress.h>
#include <Kernel/VM/AllocationStrategy.h>
#include <Kernel/VM/MemoryManager.h>
#include <Kernel/VM/PageFaultResponse.h>
#include <Kernel/VM/VMObject.h>

namespace Kernel {

class CommittedCowPages : public RefCounted<CommittedCowPages> {
    AK_MAKE_NONCOPYABLE(CommittedCowPages);

public:
    CommittedCowPages() = delete;

    explicit CommittedCowPages(size_t);
    ~CommittedCowPages();

    [[nodiscard]] NonnullRefPtr<PhysicalPage> allocate_one();
    [[nodiscard]] size_t is_empty() const { return m_committed_pages == 0; }

public:
    size_t m_committed_pages { 0 };
};

class AnonymousVMObject final : public VMObject {
public:
    virtual ~AnonymousVMObject() override;

    static RefPtr<AnonymousVMObject> try_create_with_size(size_t, AllocationStrategy);
    static RefPtr<AnonymousVMObject> try_create_for_physical_range(PhysicalAddress paddr, size_t size);
    static RefPtr<AnonymousVMObject> try_create_with_physical_pages(Span<NonnullRefPtr<PhysicalPage>>);
    static RefPtr<AnonymousVMObject> try_create_purgeable_with_size(size_t, AllocationStrategy);
    static RefPtr<AnonymousVMObject> try_create_physically_contiguous_with_size(size_t);
    virtual RefPtr<VMObject> try_clone() override;

    [[nodiscard]] NonnullRefPtr<PhysicalPage> allocate_committed_page(Badge<Region>);
    PageFaultResponse handle_cow_fault(size_t, VirtualAddress);
    size_t cow_pages() const;
    bool should_cow(size_t page_index, bool) const;
    void set_should_cow(size_t page_index, bool);

    bool is_purgeable() const { return m_purgeable; }
    bool is_volatile() const { return m_volatile; }

    KResult set_volatile(bool is_volatile, bool& was_purged);

    size_t purge();

private:
    explicit AnonymousVMObject(size_t, AllocationStrategy);
    explicit AnonymousVMObject(PhysicalAddress, size_t);
    explicit AnonymousVMObject(Span<NonnullRefPtr<PhysicalPage>>);
    explicit AnonymousVMObject(AnonymousVMObject const&);

    virtual StringView class_name() const override { return "AnonymousVMObject"sv; }

    AnonymousVMObject& operator=(AnonymousVMObject const&) = delete;
    AnonymousVMObject& operator=(AnonymousVMObject&&) = delete;
    AnonymousVMObject(AnonymousVMObject&&) = delete;

    virtual bool is_anonymous() const override { return true; }

    Bitmap& ensure_cow_map();
    void ensure_or_reset_cow_map();

    size_t m_unused_committed_pages { 0 };
    Bitmap m_cow_map;

    // We share a pool of committed cow-pages with clones
    RefPtr<CommittedCowPages> m_shared_committed_cow_pages;

    bool m_purgeable { false };
    bool m_volatile { false };
    bool m_was_purged { false };
};

}