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// Copyright 2019 The Dawn & Tint Authors
//
// 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.
//
// 3. Neither the name of the copyright holder nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// 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.
#ifndef SRC_DAWN_NATIVE_BUDDYALLOCATOR_H_
#define SRC_DAWN_NATIVE_BUDDYALLOCATOR_H_
#include <cstddef>
#include <cstdint>
#include <limits>
#include <vector>
namespace dawn::native {
// Buddy allocator uses the buddy memory allocation technique to satisfy an allocation request.
// Memory is split into halves until just large enough to fit to the request. This
// requires the allocation size to be a power-of-two value. The allocator "allocates" a block by
// returning the starting offset whose size is guaranteed to be greater than or equal to the
// allocation size. To deallocate, the same offset is used to find the corresponding block.
//
// Internally, it manages a free list to track free blocks in a full binary tree.
// Every index in the free list corresponds to a level in the tree. That level also determines
// the size of the block to be used to satisfy the request. The first level (index=0) represents
// the root whose size is also called the max block size.
//
class BuddyAllocator {
public:
explicit BuddyAllocator(uint64_t maxSize);
~BuddyAllocator();
// Required methods.
uint64_t Allocate(uint64_t allocationSize, uint64_t alignment = 1);
void Deallocate(uint64_t offset);
// For testing purposes only.
uint64_t ComputeTotalNumOfFreeBlocksForTesting() const;
static constexpr uint64_t kInvalidOffset = std::numeric_limits<uint64_t>::max();
private:
uint32_t ComputeLevelFromBlockSize(uint64_t blockSize) const;
uint64_t GetNextFreeAlignedBlock(size_t allocationBlockLevel, uint64_t alignment) const;
enum class BlockState { Free, Split, Allocated };
struct BuddyBlock {
BuddyBlock(uint64_t size, uint64_t offset)
: mOffset(offset), mSize(size), mState(BlockState::Free) {
free.pPrev = nullptr;
free.pNext = nullptr;
}
uint64_t mOffset;
uint64_t mSize;
// Pointer to this block's buddy, iff parent is split.
// Used to quickly merge buddy blocks upon de-allocate.
BuddyBlock* pBuddy = nullptr;
BuddyBlock* pParent = nullptr;
// Track whether this block has been split or not.
BlockState mState;
struct FreeLinks {
BuddyBlock* pPrev;
BuddyBlock* pNext;
};
struct SplitLink {
BuddyBlock* pLeft;
};
union {
// Used upon allocation.
// Avoids searching for the next free block.
FreeLinks free;
// Used upon de-allocation.
// Had this block split upon allocation, it and it's buddy is to be deleted.
SplitLink split;
};
};
void InsertFreeBlock(BuddyBlock* block, size_t level);
void RemoveFreeBlock(BuddyBlock* block, size_t level);
void DeleteBlock(BuddyBlock* block);
uint64_t ComputeNumOfFreeBlocks(BuddyBlock* block) const;
// Keep track the head and tail (for faster insertion/removal).
struct BlockList {
BuddyBlock* head = nullptr; // First free block in level.
// TODO(crbug.com/dawn/827): Track the tail.
};
BuddyBlock* mRoot = nullptr; // Used to deallocate non-free blocks.
uint64_t mMaxBlockSize = 0;
// List of linked-lists of free blocks where the index is a level that
// corresponds to a power-of-two sized block.
std::vector<BlockList> mFreeLists;
};
} // namespace dawn::native
#endif // SRC_DAWN_NATIVE_BUDDYALLOCATOR_H_