Source/bmalloc/bmalloc/HeapConstants.cpp

/*
 * Copyright (C) 2014-2019 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
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 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 */

#include "HeapConstants.h"
#include <algorithm>

namespace bmalloc {

DEFINE_STATIC_PER_PROCESS_STORAGE(HeapConstants);

HeapConstants::HeapConstants(const std::lock_guard<Mutex>&)
    : m_vmPageSizePhysical { vmPageSizePhysical() }
{
    RELEASE_BASSERT(m_vmPageSizePhysical >= smallPageSize);
    RELEASE_BASSERT(vmPageSize() >= m_vmPageSizePhysical);

    initializeLineMetadata();
    initializePageMetadata();
}

template <class C>
constexpr void fillLineMetadata(C& container, size_t VMPageSize)
{
    constexpr size_t clsCount = sizeClass(smallLineSize);
    size_t lineCount = smallLineCount(VMPageSize);

    for (size_t cls = 0; cls < clsCount; ++cls) {
        size_t size = objectSize(cls);
        size_t baseIndex = cls * lineCount;
        size_t object = 0;
        while (object < VMPageSize) {
            size_t line = object / smallLineSize;
            size_t leftover = object % smallLineSize;

            auto objectCount = divideRoundingUp(smallLineSize - leftover, size);

            object += objectCount * size;

            // Don't allow the last object in a page to escape the page.
            if (object > VMPageSize) {
                BASSERT(objectCount);
                --objectCount;
            }

            container[baseIndex + line] = { static_cast<unsigned char>(leftover), static_cast<unsigned char>(objectCount) };
        }
    }
}

template <size_t VMPageSize>
constexpr auto computeLineMetadata()
{
    std::array<LineMetadata, sizeClass(smallLineSize) * smallLineCount(VMPageSize)> result;
    fillLineMetadata(result, VMPageSize);
    return result;
}

#if BUSE(PRECOMPUTED_CONSTANTS_VMPAGE4K)
constexpr auto kPrecalcuratedLineMetadata4k = computeLineMetadata<4 * kB>();
#endif

#if BUSE(PRECOMPUTED_CONSTANTS_VMPAGE16K)
constexpr auto kPrecalcuratedLineMetadata16k = computeLineMetadata<16 * kB>();
#endif

void HeapConstants::initializeLineMetadata()
{
#if BUSE(PRECOMPUTED_CONSTANTS_VMPAGE4K)
    if (m_vmPageSizePhysical == 4 * kB) {
        m_smallLineMetadata = &kPrecalcuratedLineMetadata4k[0];
        return;
    }
#endif

#if BUSE(PRECOMPUTED_CONSTANTS_VMPAGE16K)
    if (m_vmPageSizePhysical == 16 * kB) {
        m_smallLineMetadata = &kPrecalcuratedLineMetadata16k[0];
        return;
    }
#endif

    size_t sizeClassCount = bmalloc::sizeClass(smallLineSize);
    m_smallLineMetadataStorage.grow(sizeClassCount * smallLineCount());
    fillLineMetadata(m_smallLineMetadataStorage, m_vmPageSizePhysical);
    m_smallLineMetadata = &m_smallLineMetadataStorage[0];
}

void HeapConstants::initializePageMetadata()
{
    auto computePageSize = [&](size_t sizeClass) {
        size_t size = objectSize(sizeClass);
        if (sizeClass < bmalloc::sizeClass(smallLineSize))
            return m_vmPageSizePhysical;

        for (size_t pageSize = m_vmPageSizePhysical; pageSize < pageSizeMax; pageSize += m_vmPageSizePhysical) {
            RELEASE_BASSERT(pageSize <= chunkSize / 2);
            size_t waste = pageSize % size;
            if (waste <= pageSize / pageSizeWasteFactor)
                return pageSize;
        }

        return pageSizeMax;
    };

    for (size_t i = 0; i < sizeClassCount; ++i)
        m_pageClasses[i] = (computePageSize(i) - 1) / smallPageSize;
}

} // namespace bmalloc