Improve the allocation algorithm in PoolChunk
Motivation: Depth-first search is not always efficient for buddy allocation. Modification: Employ a new faster search algorithm with different memoryMap layout. Result: With thread-local cache disabled, we see a lot of performance improvment, especially when the size of the allocation is as small as the page size, which had the largest search space previously: -- master head -- Benchmark (size) Mode Score Error Units pooledDirectAllocAndFree 8192 thrpt 215.392 1.565 ops/ms pooledDirectAllocAndFree 16384 thrpt 594.625 2.154 ops/ms pooledDirectAllocAndFree 65536 thrpt 1221.520 18.965 ops/ms pooledHeapAllocAndFree 8192 thrpt 217.175 1.653 ops/ms pooledHeapAllocAndFree 16384 thrpt 587.250 14.827 ops/ms pooledHeapAllocAndFree 65536 thrpt 1217.023 44.963 ops/ms -- changes -- Benchmark (size) Mode Score Error Units pooledDirectAllocAndFree 8192 thrpt 3656.744 94.093 ops/ms pooledDirectAllocAndFree 16384 thrpt 4087.152 22.921 ops/ms pooledDirectAllocAndFree 65536 thrpt 4058.814 29.276 ops/ms pooledHeapAllocAndFree 8192 thrpt 3640.355 44.418 ops/ms pooledHeapAllocAndFree 16384 thrpt 4030.206 24.365 ops/ms pooledHeapAllocAndFree 65536 thrpt 4103.991 70.991 ops/ms
This commit is contained in:
Pavan Kumar
Trustin Lee
parent
58f4b4b7d9
commit
004ffbad90
@ -16,25 +16,124 @@
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package io.netty.buffer;
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import io.netty.util.collection.IntObjectHashMap;
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/**
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* Description of algorithm for PageRun/PoolSubpage allocation from PoolChunk
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*
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* Notation: The following terms are important to understand the code
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* > page - a page is the smallest unit of memory chunk that can be allocated
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* > chunk - a chunk is a collection of pages
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* > in this code chunkSize = 2^{maxOrder} * pageSize
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*
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* To begin we allocate a byte array of size = chunkSize
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* Whenever a ByteBuf of given size needs to be created we search for the first position
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* in the byte array that has enough empty space to accommodate the requested size and
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* return a (long) handle that encodes this offset information, (this memory segment is then
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* marked as reserved so it is always used by exactly one ByteBuf and no more)
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*
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* For simplicity all sizes are normalized according to PoolArena#normalizeCapacity method
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* This ensures that when we request for memory segments of size >= pageSize the normalizedCapacity
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* equals the next nearest power of 2
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*
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* To search for the first offset in chunk that has at least requested size available we construct a
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* complete balanced binary tree and store it in an array (just like heaps) - memoryMap
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*
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* The tree looks like this (the size of each node being mentioned in the parenthesis)
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*
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* depth=0 1 node (chunkSize)
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* depth=1 2 nodes (chunkSize/2)
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* ..
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* ..
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* depth=d 2^d nodes (chunkSize/2^d)
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* ..
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* depth=maxOrder 2^maxOrder nodes (chunkSize/2^{maxOrder} = pageSize)
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*
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* depth=maxOrder is the last level and the leafs consist of pages
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*
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* With this tree available searching in chunkArray translates like this:
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* To allocate a memory segment of size chunkSize/2^k we search for the first node (from left) at height k
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* which is unused
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*
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* Algorithm:
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* ----------
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* Encode the tree in memoryMap with the notation
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* memoryMap[id] = x => in the subtree rooted at id, the first node that is free to be allocated
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* is at depth x (counted from depth=0) i.e., at depths [depth_of_id, x), there is no node that is free
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*
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* As we allocate & free nodes, we update values stored in memoryMap so that the property is maintained
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*
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* Initialization -
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* In the beginning we construct the memoryMap array by storing the depth of a node at each node
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* i.e., memoryMap[id] = depth_of_id
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*
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* Observations:
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* -------------
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* 1) memoryMap[id] = depth_of_id => it is free / unallocated
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* 2) memoryMap[id] > depth_of_id => at least one of its child nodes is allocated, so we cannot allocate it, but
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* some of its children can still be allocated based on their availability
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* 3) memoryMap[id] = maxOrder + 1 => the node is fully allocated & thus none of its children can be allocated, it
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* is thus marked as unusable
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*
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* Algorithm: [allocateNode(d) => we want to find the first node (from left) at height h that can be allocated]
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* ----------
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* 1) start at root (i.e., depth = 0 or id = 1)
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* 2) if memoryMap[1] > d => cannot be allocated from this chunk
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* 3) if left node value <= h; we can allocate from left subtree so move to left and repeat until found
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* 4) else try in right subtree
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*
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* Algorithm: [allocateRun(size)]
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* ----------
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* 1) Compute d = log_2(chunkSize/size)
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* 2) Return allocateNode(d)
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*
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* Algorithm: [allocateSubpage(size)]
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* ----------
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* All subpages allocated are stored in a map at key = elemSize
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* 1) if subpage at elemSize != null: try allocating from it.
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* if it fails: allocateSubpageSimple
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* 2) else: just allocateSubpageSimple
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*
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* Algorithm: [allocateSubpageSimple(size)]
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* ----------
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* 1) use allocateRun(maxOrder) to find an empty (i.e., unused) leaf (i.e., page)
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* 2) use this handle to construct the poolsubpage object or if it already exists just initialize it
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* with required normCapacity
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* 3) store (insert/ overwrite) the subpage in elemSubpages map for easier access
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*
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* Note:
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* -----
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* In the implementation for improving cache coherence,
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* we store 2 pieces of information (i.e, 2 byte vals) as a short value in memoryMap
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*
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* memoryMap[id]= (depth_of_id, x)
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* where as per convention defined above
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* the second value (i.e, x) indicates that the first node which is free to be allocated is at depth x (from root)
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*/
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final class PoolChunk<T> {
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private static final int ST_UNUSED = 0;
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private static final int ST_BRANCH = 1;
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private static final int ST_ALLOCATED = 2;
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private static final int ST_ALLOCATED_SUBPAGE = 3;
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private static final int BYTE_LENGTH = 8;
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private static final int BYTE_MASK = 0xFF;
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private static final int INV_BYTE_MASK = ~ BYTE_MASK;
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final PoolArena<T> arena;
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final T memory;
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final boolean unpooled;
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private final int[] memoryMap;
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private final short[] memoryMap;
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private final PoolSubpage<T>[] subpages;
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private final IntObjectHashMap<PoolSubpage<T>> elemSubpages;
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/** Used to determine if the requested capacity is equal to or greater than pageSize. */
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private final int subpageOverflowMask;
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private final int pageSize;
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private final int pageShifts;
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private final int maxOrder;
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private final int chunkSize;
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private final int log2ChunkSize;
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private final int maxSubpageAllocs;
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/** Used to mark memory as unusable */
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private final byte unusable;
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private int freeBytes;
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@ -51,25 +150,31 @@ final class PoolChunk<T> {
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this.memory = memory;
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this.pageSize = pageSize;
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this.pageShifts = pageShifts;
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this.maxOrder = maxOrder;
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this.chunkSize = chunkSize;
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unusable = (byte) (maxOrder + 1);
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log2ChunkSize = Integer.SIZE - 1 - Integer.numberOfLeadingZeros(chunkSize);
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subpageOverflowMask = ~(pageSize - 1);
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freeBytes = chunkSize;
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int chunkSizeInPages = chunkSize >>> pageShifts;
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assert maxOrder < 30 : "maxOrder should be < 30, but is : " + maxOrder;
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maxSubpageAllocs = 1 << maxOrder;
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// Generate the memory map.
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memoryMap = new int[maxSubpageAllocs << 1];
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memoryMap = new short[maxSubpageAllocs << 1];
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int memoryMapIndex = 1;
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for (int i = 0; i <= maxOrder; i ++) {
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int runSizeInPages = chunkSizeInPages >>> i;
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for (int j = 0; j < chunkSizeInPages; j += runSizeInPages) {
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//noinspection PointlessBitwiseExpression
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memoryMap[memoryMapIndex ++] = j << 17 | runSizeInPages << 2 | ST_UNUSED;
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for (int d = 0; d <= maxOrder; ++d) { // move down the tree one level at a time
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short dd = (short) ((d << BYTE_LENGTH) | d);
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for (int p = 0; p < (1 << d); ++p) {
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// in each level traverse left to right and set the depth of subtree
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// that is completely free to be my depth since I am totally free to start with
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memoryMap[memoryMapIndex] = dd;
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memoryMapIndex += 1;
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}
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}
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subpages = newSubpageArray(maxSubpageAllocs);
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elemSubpages = new IntObjectHashMap<PoolSubpage<T>>(pageShifts);
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}
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/** Creates a special chunk that is not pooled. */
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@ -79,10 +184,14 @@ final class PoolChunk<T> {
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this.memory = memory;
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memoryMap = null;
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subpages = null;
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elemSubpages = null;
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subpageOverflowMask = 0;
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pageSize = 0;
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pageShifts = 0;
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maxOrder = 0;
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unusable = (byte) (maxOrder + 1);
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chunkSize = size;
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log2ChunkSize = Integer.SIZE - 1 - Integer.numberOfLeadingZeros(chunkSize);
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maxSubpageAllocs = 0;
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}
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@ -104,218 +213,141 @@ final class PoolChunk<T> {
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}
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long allocate(int normCapacity) {
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int firstVal = memoryMap[1];
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if ((normCapacity & subpageOverflowMask) != 0) { // >= pageSize
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return allocateRun(normCapacity, 1, firstVal);
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return allocateRun(normCapacity);
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} else {
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return allocateSubpage(normCapacity, 1, firstVal);
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return allocateSubpage(normCapacity);
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}
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}
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private long allocateRun(int normCapacity, int curIdx, int val) {
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switch (val & 3) {
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case ST_UNUSED:
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return allocateRunSimple(normCapacity, curIdx, val);
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case ST_BRANCH:
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// Try the right node first because it is more likely to be ST_UNUSED.
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// It is because allocateRunSimple() always chooses the left node.
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final int nextIdxLeft = curIdx << 1;
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final int nextIdxRight = nextIdxLeft ^ 1;
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final int nextValRight = memoryMap[nextIdxRight];
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final boolean recurseRight;
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switch (nextValRight & 3) {
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case ST_UNUSED:
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return allocateRunSimple(normCapacity, nextIdxRight, nextValRight);
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case ST_BRANCH:
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recurseRight = true;
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break;
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default:
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recurseRight = false;
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}
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final int nextValLeft = memoryMap[nextIdxLeft];
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final boolean recurseLeft;
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switch (nextValLeft & 3) {
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case ST_UNUSED:
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return allocateRunSimple(normCapacity, nextIdxLeft, nextValLeft);
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case ST_BRANCH:
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recurseLeft = true;
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break;
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default:
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recurseLeft = false;
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}
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if (recurseRight) {
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long res = branchRun(normCapacity, nextIdxRight);
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if (res > 0) {
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return res;
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/**
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* Update method used by allocate
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* This is triggered only when a successor is allocated and all its predecessors
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* need to update their state
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* The minimal depth at which subtree rooted at id has some free space
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* @param id id
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*/
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private void updateParentsAlloc(int id) {
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while (id > 1) {
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int parentId = id >>> 1;
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byte mem1 = value(id);
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byte mem2 = value(id ^ 1);
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byte mem = mem1 < mem2 ? mem1 : mem2;
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setVal(parentId, mem);
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id = parentId;
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}
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}
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if (recurseLeft) {
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return branchRun(normCapacity, nextIdxLeft);
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/**
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* Update method used by free
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* This needs to handle the special case when both children are completely free
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* in which case parent be directly allocated on request of size = child-size * 2
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* @param id id
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*/
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private void updateParentsFree(int id) {
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int logChild = depth(id) + 1;
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while (id > 1) {
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int parentId = id >>> 1;
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byte mem1 = value(id);
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byte mem2 = value(id ^ 1);
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byte mem = mem1 < mem2 ? mem1 : mem2;
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setVal(parentId, mem);
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logChild -= 1; // in first iteration equals log, subsequently reduce 1 from logChild as we traverse up
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if (mem1 == logChild && mem2 == logChild) {
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setVal(parentId, (byte) (logChild - 1));
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}
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id = parentId;
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}
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}
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private int allocateNode(int d) {
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int id = 1;
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byte mem = value(id);
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if (mem > d) { // unusable
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return -1;
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}
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private long branchRun(int normCapacity, int nextIdx) {
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int nextNextIdx = nextIdx << 1;
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int nextNextVal = memoryMap[nextNextIdx];
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long res = allocateRun(normCapacity, nextNextIdx, nextNextVal);
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if (res > 0) {
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return res;
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}
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nextNextIdx ^= 1;
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nextNextVal = memoryMap[nextNextIdx];
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return allocateRun(normCapacity, nextNextIdx, nextNextVal);
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}
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private long allocateRunSimple(int normCapacity, int curIdx, int val) {
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int runLength = runLength(val);
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if (normCapacity > runLength) {
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return -1;
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}
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for (;;) {
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if (normCapacity == runLength) {
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// Found the run that fits.
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// Note that capacity has been normalized already, so we don't need to deal with
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// the values that are not power of 2.
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memoryMap[curIdx] = val & ~3 | ST_ALLOCATED;
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freeBytes -= runLength;
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return curIdx;
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}
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int nextIdx = curIdx << 1;
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int unusedIdx = nextIdx ^ 1;
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memoryMap[curIdx] = val & ~3 | ST_BRANCH;
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//noinspection PointlessBitwiseExpression
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memoryMap[unusedIdx] = memoryMap[unusedIdx] & ~3 | ST_UNUSED;
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runLength >>>= 1;
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curIdx = nextIdx;
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val = memoryMap[curIdx];
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while (mem < d || (id & (1 << d)) == 0) {
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id = id << 1;
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mem = value(id);
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if (mem > d) {
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id = id ^ 1;
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mem = value(id);
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}
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}
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private long allocateSubpage(int normCapacity, int curIdx, int val) {
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switch (val & 3) {
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case ST_UNUSED:
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return allocateSubpageSimple(normCapacity, curIdx, val);
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case ST_BRANCH:
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// Try the right node first because it is more likely to be ST_UNUSED.
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// It is because allocateSubpageSimple() always chooses the left node.
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final int nextIdxLeft = curIdx << 1;
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final int nextIdxRight = nextIdxLeft ^ 1;
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long res = branchSubpage(normCapacity, nextIdxRight);
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if (res > 0) {
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return res;
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setVal(id, unusable); // mark as unusable : because, maximum input d = maxOrder
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updateParentsAlloc(id);
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return id;
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}
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return branchSubpage(normCapacity, nextIdxLeft);
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case ST_ALLOCATED_SUBPAGE:
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PoolSubpage<T> subpage = subpages[subpageIdx(curIdx)];
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int elemSize = subpage.elemSize;
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if (normCapacity != elemSize) {
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return -1;
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private long allocateRun(int normCapacity) {
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int numPages = normCapacity >>> pageShifts;
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int d = maxOrder - (Integer.SIZE - 1 - Integer.numberOfLeadingZeros(numPages));
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int id = allocateNode(d);
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if (id < 0) {
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return id;
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}
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freeBytes -= runLength(id);
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return id;
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}
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return subpage.allocate();
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private long allocateSubpage(int normCapacity) {
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PoolSubpage<T> subpage = elemSubpages.get(normCapacity);
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if (subpage != null) {
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long handle = subpage.allocate();
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if (handle >= 0) {
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return handle;
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}
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// if subpage full (i.e., handle < 0) then replace in elemSubpage with new subpage
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}
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return allocateSubpageSimple(normCapacity);
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}
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return -1;
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private long allocateSubpageSimple(int normCapacity) {
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int d = maxOrder; // subpages are only be allocated from pages i.e., leaves
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int id = allocateNode(d);
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if (id < 0) {
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return id;
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}
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freeBytes -= pageSize;
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private long allocateSubpageSimple(int normCapacity, int curIdx, int val) {
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int runLength = runLength(val);
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for (;;) {
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if (runLength == pageSize) {
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memoryMap[curIdx] = val & ~3 | ST_ALLOCATED_SUBPAGE;
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freeBytes -= runLength;
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int subpageIdx = subpageIdx(curIdx);
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int subpageIdx = subpageIdx(id);
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PoolSubpage<T> subpage = subpages[subpageIdx];
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if (subpage == null) {
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subpage = new PoolSubpage<T>(this, curIdx, runOffset(val), pageSize, normCapacity);
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subpage = new PoolSubpage<T>(this, id, runOffset(id), pageSize, normCapacity);
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subpages[subpageIdx] = subpage;
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} else {
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subpage.init(normCapacity);
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}
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elemSubpages.put(normCapacity, subpage); // store subpage at proper elemSize pos
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return subpage.allocate();
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}
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int nextIdx = curIdx << 1;
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int unusedIdx = nextIdx ^ 1;
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memoryMap[curIdx] = val & ~3 | ST_BRANCH;
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//noinspection PointlessBitwiseExpression
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memoryMap[unusedIdx] = memoryMap[unusedIdx] & ~3 | ST_UNUSED;
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runLength >>>= 1;
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curIdx = nextIdx;
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val = memoryMap[curIdx];
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}
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}
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private long branchSubpage(int normCapacity, int nextIdx) {
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int nextVal = memoryMap[nextIdx];
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if ((nextVal & 3) != ST_ALLOCATED) {
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return allocateSubpage(normCapacity, nextIdx, nextVal);
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}
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return -1;
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}
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void free(long handle) {
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int memoryMapIdx = (int) handle;
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int bitmapIdx = (int) (handle >>> 32);
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int val = memoryMap[memoryMapIdx];
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int state = val & 3;
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if (state == ST_ALLOCATED_SUBPAGE) {
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assert bitmapIdx != 0;
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if (bitmapIdx != 0) { // free a subpage
|
||||
PoolSubpage<T> subpage = subpages[subpageIdx(memoryMapIdx)];
|
||||
assert subpage != null && subpage.doNotDestroy;
|
||||
if (subpage.free(bitmapIdx & 0x3FFFFFFF)) {
|
||||
return;
|
||||
}
|
||||
} else {
|
||||
assert state == ST_ALLOCATED : "state: " + state;
|
||||
assert bitmapIdx == 0;
|
||||
}
|
||||
|
||||
freeBytes += runLength(val);
|
||||
|
||||
for (;;) {
|
||||
//noinspection PointlessBitwiseExpression
|
||||
memoryMap[memoryMapIdx] = val & ~3 | ST_UNUSED;
|
||||
if (memoryMapIdx == 1) {
|
||||
assert freeBytes == chunkSize;
|
||||
return;
|
||||
}
|
||||
|
||||
if ((memoryMap[siblingIdx(memoryMapIdx)] & 3) != ST_UNUSED) {
|
||||
break;
|
||||
}
|
||||
|
||||
memoryMapIdx = parentIdx(memoryMapIdx);
|
||||
val = memoryMap[memoryMapIdx];
|
||||
}
|
||||
freeBytes += runLength(memoryMapIdx);
|
||||
setVal(memoryMapIdx, depth(memoryMapIdx));
|
||||
updateParentsFree(memoryMapIdx);
|
||||
}
|
||||
|
||||
void initBuf(PooledByteBuf<T> buf, long handle, int reqCapacity) {
|
||||
int memoryMapIdx = (int) handle;
|
||||
int bitmapIdx = (int) (handle >>> 32);
|
||||
if (bitmapIdx == 0) {
|
||||
int val = memoryMap[memoryMapIdx];
|
||||
assert (val & 3) == ST_ALLOCATED : String.valueOf(val & 3);
|
||||
buf.init(this, handle, runOffset(val), reqCapacity, runLength(val));
|
||||
byte val = value(memoryMapIdx);
|
||||
assert val == (maxOrder + 1) : String.valueOf(val);
|
||||
buf.init(this, handle, runOffset(memoryMapIdx), reqCapacity, runLength(memoryMapIdx));
|
||||
} else {
|
||||
initBufWithSubpage(buf, handle, bitmapIdx, reqCapacity);
|
||||
}
|
||||
@ -329,8 +361,6 @@ final class PoolChunk<T> {
|
||||
assert bitmapIdx != 0;
|
||||
|
||||
int memoryMapIdx = (int) handle;
|
||||
int val = memoryMap[memoryMapIdx];
|
||||
assert (val & 3) == ST_ALLOCATED_SUBPAGE;
|
||||
|
||||
PoolSubpage<T> subpage = subpages[subpageIdx(memoryMapIdx)];
|
||||
assert subpage.doNotDestroy;
|
||||
@ -338,29 +368,38 @@ final class PoolChunk<T> {
|
||||
|
||||
buf.init(
|
||||
this, handle,
|
||||
runOffset(val) + (bitmapIdx & 0x3FFFFFFF) * subpage.elemSize, reqCapacity, subpage.elemSize);
|
||||
runOffset(memoryMapIdx) + (bitmapIdx & 0x3FFFFFFF) * subpage.elemSize, reqCapacity, subpage.elemSize);
|
||||
}
|
||||
|
||||
private static int parentIdx(int memoryMapIdx) {
|
||||
return memoryMapIdx >>> 1;
|
||||
private byte value(int id) {
|
||||
return (byte) (memoryMap[id] & BYTE_MASK);
|
||||
}
|
||||
|
||||
private static int siblingIdx(int memoryMapIdx) {
|
||||
return memoryMapIdx ^ 1;
|
||||
private void setVal(int id, byte val) {
|
||||
memoryMap[id] = (short) ((memoryMap[id] & INV_BYTE_MASK) | val);
|
||||
}
|
||||
|
||||
private int runLength(int val) {
|
||||
return (val >>> 2 & 0x7FFF) << pageShifts;
|
||||
private byte depth(int id) {
|
||||
short val = memoryMap[id];
|
||||
return (byte) (val >>> BYTE_LENGTH);
|
||||
}
|
||||
|
||||
private int runOffset(int val) {
|
||||
return val >>> 17 << pageShifts;
|
||||
private int runLength(int id) {
|
||||
// represents the size in #bytes supported by node 'id' in the tree
|
||||
return 1 << (log2ChunkSize - depth(id));
|
||||
}
|
||||
|
||||
private int runOffset(int id) {
|
||||
// represents the 0-based offset in #bytes from start of the byte-array chunk
|
||||
int shift = id - (1 << depth(id));
|
||||
return shift * runLength(id);
|
||||
}
|
||||
|
||||
private int subpageIdx(int memoryMapIdx) {
|
||||
return memoryMapIdx - maxSubpageAllocs;
|
||||
}
|
||||
|
||||
@Override
|
||||
public String toString() {
|
||||
StringBuilder buf = new StringBuilder();
|
||||
buf.append("Chunk(");
|
||||
|
||||
Loading…
Reference in New Issue
Block a user