// _Defragment
void
BlockAllocator::Area::_Defragment()
{
D(SanityCheck());
//PRINT(("BlockAllocator::Area::_Defragment()\n"));
// A trivial strategy for now: Keep the last free block and move the
// others so that they can be joined with it. This is done iteratively
// by moving the first free block to adjoin to the second one and
// coalescing them. A free block is moved by moving the data blocks in
// between.
TFreeBlock *nextFree = NULL;
while (fFirstFree && (nextFree = fFirstFree->GetNextFreeBlock()) != NULL) {
Block *prevBlock = fFirstFree->GetPreviousBlock();
Block *nextBlock = fFirstFree->GetNextBlock();
size_t size = fFirstFree->GetSize();
// Used blocks are relatively position independed. We can move them
// en bloc and only need to adjust the previous pointer of the first
// one.
if (!nextBlock->IsFree()) {
// move the used blocks
size_t chunkSize = (char*)nextFree - (char*)nextBlock;
Block *nextFreePrev = nextFree->GetPreviousBlock();
Block *movedBlock = fFirstFree;
memmove(movedBlock, nextBlock, chunkSize);
movedBlock->SetPreviousBlock(prevBlock);
// init the first free block
Block *movedNextFreePrev = (Block*)((char*)nextFreePrev - size);
fFirstFree = _MakeFreeBlock(movedBlock, chunkSize,
movedNextFreePrev, size, true, NULL, nextFree);
nextFree->SetPreviousFreeBlock(fFirstFree);
// fix the references of the moved blocks
for (Block *block = movedBlock;
block != fFirstFree;
block = block->GetNextBlock()) {
block->FixReference();
}
} else {
// uncoalesced adjoining free block: That should never happen,
// since we always coalesce as early as possible.
INFORM(("Warning: Found uncoalesced adjoining free blocks!\n"));
}
// coalesce the first two blocks
D(SanityCheck());
_CoalesceWithNext(fFirstFree);
D(SanityCheck());
}
//D(SanityCheck());
//PRINT(("BlockAllocator::Area::_Defragment() done\n"));
}
// _CoalesceWithNext
bool
BlockAllocator::Area::_CoalesceWithNext(TFreeBlock *block)
{
bool result = false;
TFreeBlock *nextFree = NULL;
if (block && (nextFree = block->GetNextFreeBlock()) != NULL
&& block->GetNextBlock() == nextFree) {
_RemoveFreeBlock(nextFree);
Block *nextBlock = nextFree->GetNextBlock();
block->SetSize(block->GetSize() + nextFree->GetSize(), nextBlock);
if (nextBlock)
nextBlock->SetPreviousBlock(block);
else
fLastBlock = block;
result = true;
}
return result;
}
