src/dawn_native/BuddyAllocator.cpp - dawn - Git at Google

 // Copyright 2019 The Dawn Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 #include "dawn_native/BuddyAllocator.h"

 #include "common/Assert.h"
 #include "common/Math.h"

 namespace dawn_native {

     BuddyAllocator::BuddyAllocator(uint64_t maxSize) : mMaxBlockSize(maxSize) {
         ASSERT(IsPowerOfTwo(maxSize));

         mFreeLists.resize(Log2(mMaxBlockSize) + 1);

         // Insert the level0 free block.
         mRoot = new BuddyBlock(maxSize, /*offset*/ 0);
         mFreeLists[0] = {mRoot};
     }

     BuddyAllocator::~BuddyAllocator() {
         if (mRoot) {
             DeleteBlock(mRoot);
         }
     }

     uint64_t BuddyAllocator::ComputeTotalNumOfFreeBlocksForTesting() const {
         return ComputeNumOfFreeBlocks(mRoot);
     }

     uint64_t BuddyAllocator::ComputeNumOfFreeBlocks(BuddyBlock* block) const {
         if (block->mState == BlockState::Free) {
             return 1;
         } else if (block->mState == BlockState::Split) {
             return ComputeNumOfFreeBlocks(block->split.pLeft) +
                    ComputeNumOfFreeBlocks(block->split.pLeft->pBuddy);
         }
         return 0;
     }

     uint32_t BuddyAllocator::ComputeLevelFromBlockSize(uint64_t blockSize) const {
         // Every level in the buddy system can be indexed by order-n where n = log2(blockSize).
         // However, mFreeList zero-indexed by level.
         // For example, blockSize=4 is Level1 if MAX_BLOCK is 8.
         return Log2(mMaxBlockSize) - Log2(blockSize);
     }

     uint64_t BuddyAllocator::GetNextFreeAlignedBlock(size_t allocationBlockLevel,
                                                      uint64_t alignment) const {
         ASSERT(IsPowerOfTwo(alignment));
         // The current level is the level that corresponds to the allocation size. The free list may
         // not contain a block at that level until a larger one gets allocated (and splits).
         // Continue to go up the tree until such a larger block exists.
         //
         // Even if the block exists at the level, it cannot be used if it's offset is unaligned.
         // When the alignment is also a power-of-two, we simply use the next free block whose size
         // is greater than or equal to the alignment value.
         //
         //  After one 8-byte allocation:
         //
         //  Level          --------------------------------
         //      0       32 |               S              |
         //                 --------------------------------
         //      1       16 |       S       |       F2     |       S - split
         //                 --------------------------------       F - free
         //      2       8  |   Aa  |   F1  |              |       A - allocated
         //                 --------------------------------
         //
         //  Allocate(size=8, alignment=8) will be satisfied by using F1.
         //  Allocate(size=8, alignment=4) will be satified by using F1.
         //  Allocate(size=8, alignment=16) will be satisified by using F2.
         //
         for (size_t ii = 0; ii <= allocationBlockLevel; ++ii) {
             size_t currLevel = allocationBlockLevel - ii;
             BuddyBlock* freeBlock = mFreeLists[currLevel].head;
             if (freeBlock && (freeBlock->mOffset % alignment == 0)) {
                 return currLevel;
             }
         }
         return kInvalidOffset;  // No free block exists at any level.
     }

     // Inserts existing free block into the free-list.
     // Called by allocate upon splitting to insert a child block into a free-list.
     // Note: Always insert into the head of the free-list. As when a larger free block at a lower
     // level was split, there were no smaller free blocks at a higher level to allocate.
     void BuddyAllocator::InsertFreeBlock(BuddyBlock* block, size_t level) {
         ASSERT(block->mState == BlockState::Free);

         // Inserted block is now the front (no prev).
         block->free.pPrev = nullptr;

         // Old head is now the inserted block's next.
         block->free.pNext = mFreeLists[level].head;

         // Block already in HEAD position (ex. right child was inserted first).
         if (mFreeLists[level].head != nullptr) {
             // Old head's previous is the inserted block.
             mFreeLists[level].head->free.pPrev = block;
         }

         mFreeLists[level].head = block;
     }

     void BuddyAllocator::RemoveFreeBlock(BuddyBlock* block, size_t level) {
         ASSERT(block->mState == BlockState::Free);

         if (mFreeLists[level].head == block) {
             // Block is in HEAD position.
             mFreeLists[level].head = mFreeLists[level].head->free.pNext;
         } else {
             // Block is after HEAD position.
             BuddyBlock* pPrev = block->free.pPrev;
             BuddyBlock* pNext = block->free.pNext;

             ASSERT(pPrev != nullptr);
             ASSERT(pPrev->mState == BlockState::Free);

             pPrev->free.pNext = pNext;

             if (pNext != nullptr) {
                 ASSERT(pNext->mState == BlockState::Free);
                 pNext->free.pPrev = pPrev;
             }
         }
     }

     uint64_t BuddyAllocator::Allocate(uint64_t allocationSize, uint64_t alignment) {
         if (allocationSize == 0 || allocationSize > mMaxBlockSize) {
             return kInvalidOffset;
         }

         // Compute the level
         const uint32_t allocationSizeToLevel = ComputeLevelFromBlockSize(allocationSize);

         ASSERT(allocationSizeToLevel < mFreeLists.size());

         uint64_t currBlockLevel = GetNextFreeAlignedBlock(allocationSizeToLevel, alignment);

         // Error when no free blocks exist (allocator is full)
         if (currBlockLevel == kInvalidOffset) {
             return kInvalidOffset;
         }

         // Split free blocks level-by-level.
         // Terminate when the current block level is equal to the computed level of the requested
         // allocation.
         BuddyBlock* currBlock = mFreeLists[currBlockLevel].head;

         for (; currBlockLevel < allocationSizeToLevel; currBlockLevel++) {
             ASSERT(currBlock->mState == BlockState::Free);

             // Remove curr block (about to be split).
             RemoveFreeBlock(currBlock, currBlockLevel);

             // Create two free child blocks (the buddies).
             const uint64_t nextLevelSize = currBlock->mSize / 2;
             BuddyBlock* leftChildBlock = new BuddyBlock(nextLevelSize, currBlock->mOffset);
             BuddyBlock* rightChildBlock =
                 new BuddyBlock(nextLevelSize, currBlock->mOffset + nextLevelSize);

             // Remember the parent to merge these back upon de-allocation.
             rightChildBlock->pParent = currBlock;
             leftChildBlock->pParent = currBlock;

             // Make them buddies.
             leftChildBlock->pBuddy = rightChildBlock;
             rightChildBlock->pBuddy = leftChildBlock;

             // Insert the children back into the free list into the next level.
             // The free list does not require a specific order. However, an order is specified as
             // it's ideal to allocate lower addresses first by having the leftmost child in HEAD.
             InsertFreeBlock(rightChildBlock, currBlockLevel + 1);
             InsertFreeBlock(leftChildBlock, currBlockLevel + 1);

             // Curr block is now split.
             currBlock->mState = BlockState::Split;
             currBlock->split.pLeft = leftChildBlock;

             // Decend down into the next level.
             currBlock = leftChildBlock;
         }

         // Remove curr block from free-list (now allocated).
         RemoveFreeBlock(currBlock, currBlockLevel);
         currBlock->mState = BlockState::Allocated;

         return currBlock->mOffset;
     }

     void BuddyAllocator::Deallocate(uint64_t offset) {
         BuddyBlock* curr = mRoot;

         // TODO(crbug.com/dawn/827): Optimize de-allocation.
         // Passing allocationSize directly will avoid the following level-by-level search;
         // however, it requires the size information to be stored outside the allocator.

         // Search for the free block node that corresponds to the block offset.
         size_t currBlockLevel = 0;
         while (curr->mState == BlockState::Split) {
             if (offset < curr->split.pLeft->pBuddy->mOffset) {
                 curr = curr->split.pLeft;
             } else {
                 curr = curr->split.pLeft->pBuddy;
             }

             currBlockLevel++;
         }

         ASSERT(curr->mState == BlockState::Allocated);

         // Ensure the block is at the correct level
         ASSERT(currBlockLevel == ComputeLevelFromBlockSize(curr->mSize));

         // Mark curr free so we can merge.
         curr->mState = BlockState::Free;

         // Merge the buddies (LevelN-to-Level0).
         while (currBlockLevel > 0 && curr->pBuddy->mState == BlockState::Free) {
             // Remove the buddy.
             RemoveFreeBlock(curr->pBuddy, currBlockLevel);

             BuddyBlock* parent = curr->pParent;

             // The buddies were inserted in a specific order but
             // could be deleted in any order.
             DeleteBlock(curr->pBuddy);
             DeleteBlock(curr);

             // Parent is now free.
             parent->mState = BlockState::Free;

             // Ascend up to the next level (parent block).
             curr = parent;
             currBlockLevel--;
         }

         InsertFreeBlock(curr, currBlockLevel);
     }

     // Helper which deletes a block in the tree recursively (post-order).
     void BuddyAllocator::DeleteBlock(BuddyBlock* block) {
         ASSERT(block != nullptr);

         if (block->mState == BlockState::Split) {
             // Delete the pair in same order we inserted.
             DeleteBlock(block->split.pLeft->pBuddy);
             DeleteBlock(block->split.pLeft);
         }
         delete block;
     }

 }  // namespace dawn_native
	// Copyright 2019 The Dawn Authors
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	#include "dawn_native/BuddyAllocator.h"

	#include "common/Assert.h"
	#include "common/Math.h"

	namespace dawn_native {

	BuddyAllocator::BuddyAllocator(uint64_t maxSize) : mMaxBlockSize(maxSize) {
	ASSERT(IsPowerOfTwo(maxSize));

	mFreeLists.resize(Log2(mMaxBlockSize) + 1);

	// Insert the level0 free block.
	mRoot = new BuddyBlock(maxSize, /offset/ 0);
	mFreeLists[0] = {mRoot};
	}

	BuddyAllocator::~BuddyAllocator() {
	if (mRoot) {
	DeleteBlock(mRoot);
	}
	}

	uint64_t BuddyAllocator::ComputeTotalNumOfFreeBlocksForTesting() const {
	return ComputeNumOfFreeBlocks(mRoot);
	}

	uint64_t BuddyAllocator::ComputeNumOfFreeBlocks(BuddyBlock* block) const {
	if (block->mState == BlockState::Free) {
	return 1;
	} else if (block->mState == BlockState::Split) {
	return ComputeNumOfFreeBlocks(block->split.pLeft) +
	ComputeNumOfFreeBlocks(block->split.pLeft->pBuddy);
	}
	return 0;
	}

	uint32_t BuddyAllocator::ComputeLevelFromBlockSize(uint64_t blockSize) const {
	// Every level in the buddy system can be indexed by order-n where n = log2(blockSize).
	// However, mFreeList zero-indexed by level.
	// For example, blockSize=4 is Level1 if MAX_BLOCK is 8.
	return Log2(mMaxBlockSize) - Log2(blockSize);
	}

	uint64_t BuddyAllocator::GetNextFreeAlignedBlock(size_t allocationBlockLevel,
	uint64_t alignment) const {
	ASSERT(IsPowerOfTwo(alignment));
	// The current level is the level that corresponds to the allocation size. The free list may
	// not contain a block at that level until a larger one gets allocated (and splits).
	// Continue to go up the tree until such a larger block exists.
	//
	// Even if the block exists at the level, it cannot be used if it's offset is unaligned.
	// When the alignment is also a power-of-two, we simply use the next free block whose size
	// is greater than or equal to the alignment value.
	//
	// After one 8-byte allocation:
	//
	// Level --------------------------------
	// 0 32 \| S \|
	// --------------------------------
	// 1 16 \| S \| F2 \| S - split
	// -------------------------------- F - free
	// 2 8 \| Aa \| F1 \| \| A - allocated
	// --------------------------------
	//
	// Allocate(size=8, alignment=8) will be satisfied by using F1.
	// Allocate(size=8, alignment=4) will be satified by using F1.
	// Allocate(size=8, alignment=16) will be satisified by using F2.
	//
	for (size_t ii = 0; ii <= allocationBlockLevel; ++ii) {
	size_t currLevel = allocationBlockLevel - ii;
	BuddyBlock* freeBlock = mFreeLists[currLevel].head;
	if (freeBlock && (freeBlock->mOffset % alignment == 0)) {
	return currLevel;
	}
	}
	return kInvalidOffset; // No free block exists at any level.
	}

	// Inserts existing free block into the free-list.
	// Called by allocate upon splitting to insert a child block into a free-list.
	// Note: Always insert into the head of the free-list. As when a larger free block at a lower
	// level was split, there were no smaller free blocks at a higher level to allocate.
	void BuddyAllocator::InsertFreeBlock(BuddyBlock* block, size_t level) {
	ASSERT(block->mState == BlockState::Free);

	// Inserted block is now the front (no prev).
	block->free.pPrev = nullptr;

	// Old head is now the inserted block's next.
	block->free.pNext = mFreeLists[level].head;

	// Block already in HEAD position (ex. right child was inserted first).
	if (mFreeLists[level].head != nullptr) {
	// Old head's previous is the inserted block.
	mFreeLists[level].head->free.pPrev = block;
	}

	mFreeLists[level].head = block;
	}

	void BuddyAllocator::RemoveFreeBlock(BuddyBlock* block, size_t level) {
	ASSERT(block->mState == BlockState::Free);

	if (mFreeLists[level].head == block) {
	// Block is in HEAD position.
	mFreeLists[level].head = mFreeLists[level].head->free.pNext;
	} else {
	// Block is after HEAD position.
	BuddyBlock* pPrev = block->free.pPrev;
	BuddyBlock* pNext = block->free.pNext;

	ASSERT(pPrev != nullptr);
	ASSERT(pPrev->mState == BlockState::Free);

	pPrev->free.pNext = pNext;

	if (pNext != nullptr) {
	ASSERT(pNext->mState == BlockState::Free);
	pNext->free.pPrev = pPrev;
	}
	}
	}

	uint64_t BuddyAllocator::Allocate(uint64_t allocationSize, uint64_t alignment) {
	if (allocationSize == 0 \|\| allocationSize > mMaxBlockSize) {
	return kInvalidOffset;
	}

	// Compute the level
	const uint32_t allocationSizeToLevel = ComputeLevelFromBlockSize(allocationSize);

	ASSERT(allocationSizeToLevel < mFreeLists.size());

	uint64_t currBlockLevel = GetNextFreeAlignedBlock(allocationSizeToLevel, alignment);

	// Error when no free blocks exist (allocator is full)
	if (currBlockLevel == kInvalidOffset) {
	return kInvalidOffset;
	}

	// Split free blocks level-by-level.
	// Terminate when the current block level is equal to the computed level of the requested
	// allocation.
	BuddyBlock* currBlock = mFreeLists[currBlockLevel].head;

	for (; currBlockLevel < allocationSizeToLevel; currBlockLevel++) {
	ASSERT(currBlock->mState == BlockState::Free);

	// Remove curr block (about to be split).
	RemoveFreeBlock(currBlock, currBlockLevel);

	// Create two free child blocks (the buddies).
	const uint64_t nextLevelSize = currBlock->mSize / 2;
	BuddyBlock* leftChildBlock = new BuddyBlock(nextLevelSize, currBlock->mOffset);
	BuddyBlock* rightChildBlock =
	new BuddyBlock(nextLevelSize, currBlock->mOffset + nextLevelSize);

	// Remember the parent to merge these back upon de-allocation.
	rightChildBlock->pParent = currBlock;
	leftChildBlock->pParent = currBlock;

	// Make them buddies.
	leftChildBlock->pBuddy = rightChildBlock;
	rightChildBlock->pBuddy = leftChildBlock;

	// Insert the children back into the free list into the next level.
	// The free list does not require a specific order. However, an order is specified as
	// it's ideal to allocate lower addresses first by having the leftmost child in HEAD.
	InsertFreeBlock(rightChildBlock, currBlockLevel + 1);
	InsertFreeBlock(leftChildBlock, currBlockLevel + 1);

	// Curr block is now split.
	currBlock->mState = BlockState::Split;
	currBlock->split.pLeft = leftChildBlock;

	// Decend down into the next level.
	currBlock = leftChildBlock;
	}

	// Remove curr block from free-list (now allocated).
	RemoveFreeBlock(currBlock, currBlockLevel);
	currBlock->mState = BlockState::Allocated;

	return currBlock->mOffset;
	}

	void BuddyAllocator::Deallocate(uint64_t offset) {
	BuddyBlock* curr = mRoot;

	// TODO(crbug.com/dawn/827): Optimize de-allocation.
	// Passing allocationSize directly will avoid the following level-by-level search;
	// however, it requires the size information to be stored outside the allocator.

	// Search for the free block node that corresponds to the block offset.
	size_t currBlockLevel = 0;
	while (curr->mState == BlockState::Split) {
	if (offset < curr->split.pLeft->pBuddy->mOffset) {
	curr = curr->split.pLeft;
	} else {
	curr = curr->split.pLeft->pBuddy;
	}

	currBlockLevel++;
	}

	ASSERT(curr->mState == BlockState::Allocated);

	// Ensure the block is at the correct level
	ASSERT(currBlockLevel == ComputeLevelFromBlockSize(curr->mSize));

	// Mark curr free so we can merge.
	curr->mState = BlockState::Free;

	// Merge the buddies (LevelN-to-Level0).
	while (currBlockLevel > 0 && curr->pBuddy->mState == BlockState::Free) {
	// Remove the buddy.
	RemoveFreeBlock(curr->pBuddy, currBlockLevel);

	BuddyBlock* parent = curr->pParent;

	// The buddies were inserted in a specific order but
	// could be deleted in any order.
	DeleteBlock(curr->pBuddy);
	DeleteBlock(curr);

	// Parent is now free.
	parent->mState = BlockState::Free;

	// Ascend up to the next level (parent block).
	curr = parent;
	currBlockLevel--;
	}

	InsertFreeBlock(curr, currBlockLevel);
	}

	// Helper which deletes a block in the tree recursively (post-order).
	void BuddyAllocator::DeleteBlock(BuddyBlock* block) {
	ASSERT(block != nullptr);

	if (block->mState == BlockState::Split) {
	// Delete the pair in same order we inserted.
	DeleteBlock(block->split.pLeft->pBuddy);
	DeleteBlock(block->split.pLeft);
	}
	delete block;
	}

	} // namespace dawn_native