MemoryPressureManager.h

/*
 * Copyright (c) 2008-2014, Pedigree Developers
 *
 * Please see the CONTRIB file in the root of the source tree for a full
 * list of contributors.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#ifndef MEMORY_PRESSURE_MANAGER_H
#define MEMORY_PRESSURE_MANAGER_H

#include "pedigree/kernel/compiler.h"
#include "pedigree/kernel/processor/types.h"
#include "pedigree/kernel/utilities/List.h"
#include "pedigree/kernel/utilities/String.h"
#include "pedigree/kernel/utilities/new"

#define MAX_MEMPRESSURE_PRIORITY 16

class EXPORTED_PUBLIC MemoryPressureHandler
{
  public:
    MemoryPressureHandler();
    virtual ~MemoryPressureHandler();

    virtual const String getMemoryPressureDescription() = 0;

    virtual bool compact() = 0;
};

class EXPORTED_PUBLIC MemoryPressureManager
{
  public:
    MemoryPressureManager();
    ~MemoryPressureManager();

    const static size_t HighestPriority = 0;
    const static size_t HighPriority = MAX_MEMPRESSURE_PRIORITY / 3;
    const static size_t MediumPriority = MAX_MEMPRESSURE_PRIORITY / 2;
    const static size_t LowPriority = (MAX_MEMPRESSURE_PRIORITY * 2) / 3;
    const static size_t LowestPriority = MAX_MEMPRESSURE_PRIORITY - 1;

    static MemoryPressureManager &instance()
    {
        return m_Instance;
    }

    static size_t getHighWatermark()
    {
        // Once the system has only this or less pages free, we begin
        // doing compacts. We do not want to wait until the system is
        // actually out of memory, as some compact mechanisms require
        // allocating memory.
        return 16;
    }

    static size_t getLowWatermark()
    {
        // Caches can begin voluntarily evicting cache pages at this mark.
        // Should no action be taken, the system will take over forcefully
        // at the high water mark.
        return 32;
    }

    bool compact();

    void registerHandler(size_t prio, MemoryPressureHandler *pHandler);

    void removeHandler(MemoryPressureHandler *pHandler);

  private:
    static MemoryPressureManager m_Instance;

    List<MemoryPressureHandler *> m_Handlers[MAX_MEMPRESSURE_PRIORITY];
};

#endif