379 lines
14 KiB
C#
379 lines
14 KiB
C#
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//
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// Copyright (c) Microsoft Corporation. All rights reserved.
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//
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/*******************************************************************/
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/* WARNING */
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/* This file should be identical in the Bartok and Singularity */
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/* depots. Master copy resides in Bartok Depot. Changes should be */
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/* made to Bartok Depot and propagated to Singularity Depot. */
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/*******************************************************************/
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namespace System.GCs {
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using System.Threading;
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using System.Runtime.InteropServices;
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using System.Runtime.CompilerServices;
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internal class ModifiedFirstFit {
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private const uint minimumBlockSize = 12;
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private static UIntPtr osCommitSize;
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private UIntPtr head;
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private UIntPtr tail;
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private UIntPtr last;
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private UIntPtr totalMemory;
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[PreInitRefCounts]
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internal static void Initialize() {
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osCommitSize = MemoryManager.OperatingSystemCommitSize;
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UIntPtr heapCommitSize = new UIntPtr(1 << 20);
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VTable.Assert(heapCommitSize > osCommitSize,
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@"heapCommitSize > osCommitSize");
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PageManager.Initialize(osCommitSize, heapCommitSize);
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}
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[Inline]
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[ManualRefCounts]
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internal UIntPtr AllocateBlock(UIntPtr blockSize,
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Thread t) {
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UIntPtr prev;
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if (head == UIntPtr.Zero) { // Free list exhausted
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// or no free list yet.
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prev = growFreeList(blockSize, t);
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} else {
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VTable.Assert(tail >= head,
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@"tail >= head");
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// Perform a first-fit search from the last
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// free block that served up an allocation
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// request, or the free block after that if
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// it was fully served (next fit).
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prev = last;
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UIntPtr desiredBlockSize = blockSize+minimumBlockSize;
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while (getBlockSize(prev) < desiredBlockSize) {
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prev = getNextBlock(prev);
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if (prev == last) { // Search has wrapped around.
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prev = growFreeList(blockSize, t);
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break;
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}
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}
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}
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// At this point, either the block pointed by "prev"
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// has a size that exceeds the requested size by
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// at least "minimumBlockSize", or precedes a block
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// whose size equals the requested size or exceeds
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// it by at least "minimumBlockSize".
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UIntPtr prevBlockSize = getBlockSize(prev);
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VTable.Assert(prevBlockSize >= blockSize+
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minimumBlockSize ||
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getBlockSize(getNextBlock(prev)) ==
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blockSize ||
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getBlockSize(getNextBlock(prev)) >=
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blockSize+minimumBlockSize,
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@"prevBlockSize >= blockSize+
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minimumBlockSize ||
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getBlockSize(getNextBlock(prev)) ==
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blockSize ||
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getBlockSize(getNextBlock(prev)) >=
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blockSize+minimumBlockSize");
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UIntPtr resultAddr;
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if (prevBlockSize >=
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blockSize+minimumBlockSize) { // Break block.
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setBlockSize(prev, prevBlockSize-blockSize);
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resultAddr = prev+(prevBlockSize-blockSize);
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last = prev;
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} else { // Process request from the next block.
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UIntPtr curr = getNextBlock(prev);
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UIntPtr currBlockSize = getBlockSize(curr);
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if (currBlockSize >= blockSize+minimumBlockSize) {
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setBlockSize(curr, currBlockSize-blockSize);
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resultAddr = curr+(currBlockSize-blockSize);
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last = curr;
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} else { // Return entire block.
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VTable.Assert(currBlockSize == blockSize,
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@"currBlockSize == blockSize");
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resultAddr = curr;
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if (prev == curr) { // Free list becomes empty.
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head = UIntPtr.Zero;
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tail = UIntPtr.Zero;
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last = UIntPtr.Zero;
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} else { // Skip a block in the free list.
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if (curr == head) {
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curr = getNextBlock(curr);
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setNextBlock(prev, curr);
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head = curr;
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} else if (curr == tail) {
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curr = head;
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setNextBlock(prev, curr);
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tail = prev;
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} else {
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curr = getNextBlock(curr);
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setNextBlock(prev, curr);
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}
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last = curr;
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}
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}
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}
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// Wipe out old contents.
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Util.MemClear(resultAddr, blockSize);
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// Adjust memory audit figure.
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totalMemory -= blockSize;
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return resultAddr;
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}
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// Free lists used in this implementation have the invariant
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// that their blocks are linked in increasing order of
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// addresses. FreeBlock preserves this invariant. It also
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// coalesces the inserted block with abutting free blocks.
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//
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// It returns the block just before the point of insertion.
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[Inline]
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[ManualRefCounts]
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internal UIntPtr FreeBlock(UIntPtr block, UIntPtr size) {
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VTable.Assert(block != UIntPtr.Zero,
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@"block != UIntPtr.Zero");
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VTable.Assert(head <= tail,
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@"head <= tail");
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VTable.Assert(size > 0,
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@"size > 0");
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// Adjust memory audit figure.
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totalMemory += size;
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UIntPtr below;
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if (block < head) {
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VTable.Assert(head != UIntPtr.Zero,
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@"head != UIntPtr.Zero");
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VTable.Assert(tail != UIntPtr.Zero,
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@"tail != UIntPtr.Zero");
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VTable.Assert(block+size <= head,
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@"block+size <= head");
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if (block+size == head) {
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setBlockSize(block, size+getBlockSize(head));
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if (head == tail) {
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tail = block;
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} else {
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setNextBlock(block, getNextBlock(head));
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}
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if (last == head) {
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last = block;
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}
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} else {
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setBlockSize(block, size);
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setNextBlock(block, head);
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}
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below = tail;
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setNextBlock(below, block);
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head = block;
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} else if (head == UIntPtr.Zero) {
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VTable.Assert(tail == UIntPtr.Zero,
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@"tail == UIntPtr.Zero");
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VTable.Assert(last == UIntPtr.Zero,
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@"last == UIntPtr.Zero");
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tail = block;
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setBlockSize(block, size);
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setNextBlock(block, block);
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below = block;
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head = block;
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last = block;
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} else if (block > tail) {
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VTable.Assert(tail != UIntPtr.Zero,
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@"tail != UIntPtr.Zero");
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below = tail;
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UIntPtr lastBlockSize = getBlockSize(below);
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VTable.Assert(below+lastBlockSize <= block,
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@"below+lastBlockSize <= block");
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if (below+lastBlockSize == block) {
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setBlockSize(below, lastBlockSize+size);
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} else {
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setNextBlock(below, block);
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setBlockSize(block, size);
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setNextBlock(block, head);
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tail = block;
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}
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} else {
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VTable.Assert(UIntPtr.Zero < head,
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@"UIntPtr.Zero < head");
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VTable.Assert(head < block,
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@"head < block");
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VTable.Assert(block < tail,
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@"block < tail");
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// UIntPtr.Zero < head < block < tail.
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// The blocks referenced by "below" and "above"
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// ultimately straddle the inserted block.
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below = head;
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UIntPtr above = getNextBlock(below);
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while (above < block) {
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below = above;
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above = getNextBlock(below);
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}
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// At this point, below < block < above.
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VTable.Assert(below < block,
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@"below < block");
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VTable.Assert(below+getBlockSize(below) <= block,
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@"below+getBlockSize(below) <= block");
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VTable.Assert(block < above,
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@"block < above");
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VTable.Assert(block+size <= above,
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@"block+size <= above");
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// Coalesce blocks if possible.
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if (block+size == above) {
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size += getBlockSize(above);
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setBlockSize(block, size);
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if (tail == above) {
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tail = block;
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}
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if (last == above) {
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last = block;
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}
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above = getNextBlock(above);
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} else {
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setBlockSize(block, size);
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}
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setNextBlock(block, above);
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UIntPtr belowBlockSize = getBlockSize(below);
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if (below+belowBlockSize == block) {
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setBlockSize(below, belowBlockSize+size);
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setNextBlock(below, above);
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if (tail == block) {
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tail = below;
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}
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if (last == block) {
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last = below;
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}
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} else {
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setNextBlock(below, block);
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}
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}
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return below;
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}
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internal UIntPtr TotalMemory {
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[Inline]
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[ManualRefCounts]
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get {
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return totalMemory;
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}
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}
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[Inline]
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[ManualRefCounts]
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internal unsafe void CheckConsistency() {
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if (head == UIntPtr.Zero) {
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VTable.Assert(tail == UIntPtr.Zero,
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@"tail == UIntPtr.Zero");
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} else if (tail == UIntPtr.Zero) {
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VTable.Assert(head == UIntPtr.Zero,
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@"head == UIntPtr.Zero");
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} else {
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VTable.Assert(head <= tail,
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@"head <= tail");
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VTable.Assert(getNextBlock(tail) == head,
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@"getNextBlock(tail) == head");
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UIntPtr leastBlockSize = new UIntPtr(2*sizeof(uint));
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UIntPtr block = head;
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while (block != tail) {
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UIntPtr blockSize = getBlockSize(block);
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UIntPtr nextBlock = getNextBlock(block);
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VTable.Assert(blockSize >= leastBlockSize,
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@"blockSize >= leastBlockSize");
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VTable.Assert(block+blockSize < nextBlock,
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@"block+blockSize < nextBlock");
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block = nextBlock;
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}
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VTable.Assert(getBlockSize(block) >= leastBlockSize,
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@"getBlockSize(block) >= leastBlockSize");
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}
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}
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// Grow free list by allocating and inserting a block of
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// size at least "blockSize".
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[Inline]
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[ManualRefCounts]
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private UIntPtr growFreeList(UIntPtr blockSize, Thread t) {
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UIntPtr pageCount = PageTable.PageCount(blockSize);
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bool fCleanPages = true;
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UIntPtr startPage = PageManager.EnsurePages(t, pageCount,
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PageType.Owner0,
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ref fCleanPages);
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UIntPtr newBlockSize = PageTable.RegionSize(pageCount);
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UIntPtr newBlockAddr = PageTable.PageAddr(startPage);
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return FreeBlock(newBlockAddr, newBlockSize);
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}
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// Layout of a free block:
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//
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// Low address ------> High address
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// --------------------------------
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// | | | |
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// | A | B | |
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// | | | |
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// --------------------------------
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// <----------- size ----------->
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//
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// A: UIntPtr field that contains a UIntPtr to the next block
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// on the free list.
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//
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// B: UIntPtr field that contains the size of the free block.
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private unsafe static UIntPtr getNextBlock(UIntPtr block) {
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return *((UIntPtr*)block+0);
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}
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private unsafe static void setNextBlock(UIntPtr block,
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UIntPtr nextBlock) {
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*((UIntPtr*)block+0) = nextBlock;
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}
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private unsafe static UIntPtr getBlockSize(UIntPtr block) {
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return *((UIntPtr*)block+1);
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}
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private unsafe static void setBlockSize(UIntPtr block,
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UIntPtr size) {
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*((UIntPtr*)block+1) = size;
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}
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}
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}
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