118 lines
4.2 KiB
C++
118 lines
4.2 KiB
C++
// Copyright 2019 The Dawn Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef DAWNNATIVE_BUDDYALLOCATOR_H_
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#define DAWNNATIVE_BUDDYALLOCATOR_H_
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#include <cstddef>
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#include <cstdint>
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#include <limits>
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#include <vector>
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namespace dawn_native {
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// Buddy allocator uses the buddy memory allocation technique to satisfy an allocation request.
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// Memory is split into halves until just large enough to fit to the request. This
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// requires the allocation size to be a power-of-two value. The allocator "allocates" a block by
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// returning the starting offset whose size is guaranteed to be greater than or equal to the
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// allocation size. To deallocate, the same offset is used to find the corresponding block.
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//
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// Internally, it manages a free list to track free blocks in a full binary tree.
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// Every index in the free list corresponds to a level in the tree. That level also determines
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// the size of the block to be used to satisfy the request. The first level (index=0) represents
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// the root whose size is also called the max block size.
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//
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class BuddyAllocator {
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public:
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BuddyAllocator(uint64_t maxSize);
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~BuddyAllocator();
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// Required methods.
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uint64_t Allocate(uint64_t allocationSize, uint64_t alignment = 1);
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void Deallocate(uint64_t offset);
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// For testing purposes only.
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uint64_t ComputeTotalNumOfFreeBlocksForTesting() const;
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static constexpr uint64_t kInvalidOffset = std::numeric_limits<uint64_t>::max();
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private:
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uint32_t ComputeLevelFromBlockSize(uint64_t blockSize) const;
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uint64_t GetNextFreeAlignedBlock(size_t allocationBlockLevel, uint64_t alignment) const;
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enum class BlockState { Free, Split, Allocated };
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struct BuddyBlock {
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BuddyBlock(uint64_t size, uint64_t offset)
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: mOffset(offset), mSize(size), mState(BlockState::Free) {
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free.pPrev = nullptr;
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free.pNext = nullptr;
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}
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uint64_t mOffset;
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uint64_t mSize;
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// Pointer to this block's buddy, iff parent is split.
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// Used to quickly merge buddy blocks upon de-allocate.
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BuddyBlock* pBuddy = nullptr;
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BuddyBlock* pParent = nullptr;
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// Track whether this block has been split or not.
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BlockState mState;
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struct FreeLinks {
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BuddyBlock* pPrev;
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BuddyBlock* pNext;
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};
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struct SplitLink {
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BuddyBlock* pLeft;
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};
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union {
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// Used upon allocation.
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// Avoids searching for the next free block.
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FreeLinks free;
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// Used upon de-allocation.
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// Had this block split upon allocation, it and it's buddy is to be deleted.
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SplitLink split;
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};
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};
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void InsertFreeBlock(BuddyBlock* block, size_t level);
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void RemoveFreeBlock(BuddyBlock* block, size_t level);
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void DeleteBlock(BuddyBlock* block);
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uint64_t ComputeNumOfFreeBlocks(BuddyBlock* block) const;
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// Keep track the head and tail (for faster insertion/removal).
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struct BlockList {
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BuddyBlock* head = nullptr; // First free block in level.
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// TODO(bryan.bernhart@intel.com): Track the tail.
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};
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BuddyBlock* mRoot = nullptr; // Used to deallocate non-free blocks.
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uint64_t mMaxBlockSize = 0;
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// List of linked-lists of free blocks where the index is a level that
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// corresponds to a power-of-two sized block.
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std::vector<BlockList> mFreeLists;
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};
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} // namespace dawn_native
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#endif // DAWNNATIVE_BUDDYALLOCATOR_H_
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