serenity/Kernel/VM/RangeAllocator.cpp

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * 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 notice, this
 *    list of conditions and the following disclaimer.
 *
 * 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 THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 THE COPYRIGHT HOLDER 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 PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <AK/BinarySearch.h>
#include <AK/QuickSort.h>
#include <Kernel/Random.h>
#include <Kernel/Thread.h>
#include <Kernel/VM/RangeAllocator.h>

//#define VRA_DEBUG
#define VM_GUARD_PAGES

namespace Kernel {

RangeAllocator::RangeAllocator()
{
}

void RangeAllocator::initialize_with_range(VirtualAddress base, size_t size)
{
    m_total_range = { base, size };
    m_available_ranges.append({ base, size });
#ifdef VRA_DEBUG
    dump();
#endif
}

void RangeAllocator::initialize_from_parent(const RangeAllocator& parent_allocator)
{
    m_total_range = parent_allocator.m_total_range;
    m_available_ranges = parent_allocator.m_available_ranges;
}

RangeAllocator::~RangeAllocator()
{
}

void RangeAllocator::dump() const
{
    dbg() << "RangeAllocator{" << this << "}";
    for (auto& range : m_available_ranges) {
        dbg() << "    " << String::format("%x", range.base().get()) << " -> " << String::format("%x", range.end().get() - 1);
    }
}

Vector<Range, 2> Range::carve(const Range& taken)
{
    Vector<Range, 2> parts;
    if (taken == *this)
        return {};
    if (taken.base() > base())
        parts.append({ base(), taken.base().get() - base().get() });
    if (taken.end() < end())
        parts.append({ taken.end(), end().get() - taken.end().get() });
#ifdef VRA_DEBUG
    dbg() << "VRA: carve: take " << String::format("%x", taken.base().get()) << "-" << String::format("%x", taken.end().get() - 1) << " from " << String::format("%x", base().get()) << "-" << String::format("%x", end().get() - 1);
    for (int i = 0; i < parts.size(); ++i)
        dbg() << "        " << String::format("%x", parts[i].base().get()) << "-" << String::format("%x", parts[i].end().get() - 1);
#endif
    return parts;
}

void RangeAllocator::carve_at_index(int index, const Range& range)
{
    auto remaining_parts = m_available_ranges[index].carve(range);
    ASSERT(remaining_parts.size() >= 1);
    m_available_ranges[index] = remaining_parts[0];
    if (remaining_parts.size() == 2)
        m_available_ranges.insert(index + 1, move(remaining_parts[1]));
}

Range RangeAllocator::allocate_anywhere(size_t size, size_t alignment)
{
    if (!size)
        return {};

#ifdef VM_GUARD_PAGES
    // NOTE: We pad VM allocations with a guard page on each side.
    size_t effective_size = size + PAGE_SIZE * 2;
    size_t offset_from_effective_base = PAGE_SIZE;
#else
    size_t effective_size = size;
    size_t offset_from_effective_base = 0;
#endif

    for (size_t i = 0; i < m_available_ranges.size(); ++i) {
        auto& available_range = m_available_ranges[i];
        // FIXME: This check is probably excluding some valid candidates when using a large alignment.
        if (available_range.size() < (effective_size + alignment))
            continue;

        FlatPtr initial_base = available_range.base().offset(offset_from_effective_base).get();
        FlatPtr aligned_base = round_up_to_power_of_two(initial_base, alignment);

        Range allocated_range(VirtualAddress(aligned_base), size);
        if (available_range == allocated_range) {
#ifdef VRA_DEBUG
            dbg() << "VRA: Allocated perfect-fit anywhere(" << String::format("%zu", size) << ", " << String::format("%zu", alignment) << "): " << String::format("%x", allocated_range.base().get());
#endif
            m_available_ranges.remove(i);
            return allocated_range;
        }
        carve_at_index(i, allocated_range);
#ifdef VRA_DEBUG
        dbg() << "VRA: Allocated anywhere(" << String::format("%zu", size) << ", " << String::format("%zu", alignment) << "): " << String::format("%x", allocated_range.base().get());
        dump();
#endif
        return allocated_range;
    }
    klog() << "VRA: Failed to allocate anywhere: " << size << ", " << alignment;
    return {};
}

Range RangeAllocator::allocate_specific(VirtualAddress base, size_t size)
{
    if (!size)
        return {};

    Range allocated_range(base, size);
    for (size_t i = 0; i < m_available_ranges.size(); ++i) {
        auto& available_range = m_available_ranges[i];
        if (!available_range.contains(base, size))
            continue;
        if (available_range == allocated_range) {
            m_available_ranges.remove(i);
            return allocated_range;
        }
        carve_at_index(i, allocated_range);
#ifdef VRA_DEBUG
        dbg() << "VRA: Allocated specific(" << size << "): " << String::format("%x", available_range.base().get());
        dump();
#endif
        return allocated_range;
    }
    dbg() << "VRA: Failed to allocate specific range: " << base << "(" << size << ")";
    return {};
}

void RangeAllocator::deallocate(Range range)
{
    ASSERT(m_total_range.contains(range));
    ASSERT(range.size());
    ASSERT(range.base() < range.end());

#ifdef VRA_DEBUG
    dbg() << "VRA: Deallocate: " << String::format("%x", range.base().get()) << "(" << range.size() << ")";
    dump();
#endif

    ASSERT(!m_available_ranges.is_empty());

    int nearby_index = 0;
    auto* existing_range = binary_search(
        m_available_ranges.data(), m_available_ranges.size(), range, [](auto& a, auto& b) {
            return a.base().get() - b.end().get();
        },
        &nearby_index);

    size_t inserted_index = 0;
    if (existing_range) {
        existing_range->m_size += range.size();
        inserted_index = nearby_index;
    } else {
        m_available_ranges.insert_before_matching(
            Range(range), [&](auto& entry) {
                return entry.base() >= range.end();
            },
            nearby_index, &inserted_index);
    }

    if (inserted_index < (m_available_ranges.size() - 1)) {
        // We already merged with previous. Try to merge with next.
        auto& inserted_range = m_available_ranges[inserted_index];
        auto& next_range = m_available_ranges[inserted_index + 1];
        if (inserted_range.end() == next_range.base()) {
            inserted_range.m_size += next_range.size();
            m_available_ranges.remove(inserted_index + 1);
            return;
        }
    }
#ifdef VRA_DEBUG
    dbg() << "VRA: After deallocate";
    dump();
#endif
}

}