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https://github.com/SerenityOS/serenity
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ac7ce12123
This was a premature optimization from the early days of SerenityOS. The eternal heap was a simple bump pointer allocator over a static byte array. My original idea was to avoid heap fragmentation and improve data locality, but both ideas were rooted in cargo culting, not data. We would reserve 4 MiB at boot and only ended up using ~256 KiB, wasting the rest. This patch replaces all kmalloc_eternal() usage by regular kmalloc().
95 lines
2.8 KiB
C++
95 lines
2.8 KiB
C++
/*
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* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Bitmap.h>
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#include <AK/IntrusiveList.h>
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namespace Kernel::Memory {
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// A PhysicalZone is an allocator that manages a sub-area of a PhysicalRegion.
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// Its total size is always a power of two.
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// You allocate chunks at a time. One chunk is PAGE_SIZE/2, and the minimum allocation size is 2 chunks.
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// The allocator uses a buddy block scheme internally.
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class PhysicalZone {
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AK_MAKE_NONCOPYABLE(PhysicalZone);
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AK_MAKE_NONMOVABLE(PhysicalZone);
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public:
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static constexpr size_t ZONE_CHUNK_SIZE = PAGE_SIZE / 2;
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using ChunkIndex = i16;
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PhysicalZone(PhysicalAddress base, size_t page_count);
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Optional<PhysicalAddress> allocate_block(size_t order);
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void deallocate_block(PhysicalAddress, size_t order);
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void dump() const;
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size_t available() const { return m_page_count - (m_used_chunks / 2); }
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bool is_empty() const { return available() == 0; }
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PhysicalAddress base() const { return m_base_address; }
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bool contains(PhysicalAddress paddr) const
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{
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return paddr >= m_base_address && paddr < m_base_address.offset(m_page_count * PAGE_SIZE);
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}
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private:
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Optional<ChunkIndex> allocate_block_impl(size_t order);
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void deallocate_block_impl(ChunkIndex, size_t order);
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struct BuddyBucket {
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bool get_buddy_bit(ChunkIndex index) const
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{
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return bitmap.get(buddy_bit_index(index));
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}
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void set_buddy_bit(ChunkIndex index, bool value)
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{
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bitmap.set(buddy_bit_index(index), value);
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}
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size_t buddy_bit_index(ChunkIndex index) const
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{
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// NOTE: We cut the index in half since one chunk is half a page.
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return (index >> 1) >> (1 + order);
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}
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// This bucket's index in the m_buckets array. (Redundant data kept here for convenience.)
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size_t order { 0 };
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// This is the start of the freelist for this buddy size.
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// It's an index into the global PhysicalPageEntry array (offset by this PhysicalRegion's base.)
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// A value of -1 indicates an empty freelist.
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ChunkIndex freelist { -1 };
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// Bitmap with 1 bit per buddy pair.
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// 0 == Both blocks either free or used.
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// 1 == One block free, one block used.
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Bitmap bitmap;
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};
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static constexpr size_t max_order = 12;
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BuddyBucket m_buckets[max_order + 1];
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PhysicalPageEntry& get_freelist_entry(ChunkIndex) const;
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void remove_from_freelist(BuddyBucket&, ChunkIndex);
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PhysicalAddress m_base_address { 0 };
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size_t m_page_count { 0 };
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size_t m_used_chunks { 0 };
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IntrusiveListNode<PhysicalZone> m_list_node;
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public:
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using List = IntrusiveList<&PhysicalZone::m_list_node>;
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};
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}
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