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implement rounding to word borders when allocating

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churl
2022-05-09 16:45:01 +02:00
parent 10d790f613
commit f57b8fef27
2 changed files with 20 additions and 6 deletions
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19
c_os/kernel/allocator/LinkedListAllocator.cc
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@ -88,14 +88,21 @@ void* LinkedListAllocator::alloc(unsigned int req_size) {
return NULL; return NULL;
} }
// Round to word borders
unsigned int req_size_diff = (4 - req_size % 4) % 4;
unsigned int rreq_size = req_size + req_size_diff;
if (req_size_diff > 0) {
kout << " - Rounded to word border (+" << dec << req_size_diff << " bytes)" << endl;
}
struct free_block* current = this->free_start; struct free_block* current = this->free_start;
do { do {
if (current->size >= req_size) { if (current->size >= rreq_size) {
// Current block large enough // Current block large enough
// We now have: [<> | current | <>] // We now have: [<> | current | <>]
// Don't subtract to prevent underflow // Don't subtract to prevent underflow
if (current->size >= req_size + sizeof(struct free_block) + HEAP_MIN_FREE_BLOCK_SIZE) { if (current->size >= rreq_size + sizeof(struct free_block) + HEAP_MIN_FREE_BLOCK_SIZE) {
// Block so large it can be cut // Block so large it can be cut
// Create new header after allocated memory and rearrange pointers // Create new header after allocated memory and rearrange pointers
@ -103,20 +110,20 @@ void* LinkedListAllocator::alloc(unsigned int req_size) {
// In case of only one freeblock: // In case of only one freeblock:
// [current | new_next] // [current | new_next]
struct free_block* new_next = struct free_block* new_next =
(struct free_block*)((unsigned int)current + sizeof(struct free_block) + req_size); (struct free_block*)((unsigned int)current + sizeof(struct free_block) + rreq_size);
// If only one block exists, current->next is current // If only one block exists, current->next is current
// This shouldn't be a problem since the block gets removed from the list later // This shouldn't be a problem since the block gets removed from the list later
new_next->next = current->next; new_next->next = current->next;
new_next->size = current->size - (req_size + sizeof(struct free_block)); new_next->size = current->size - (rreq_size + sizeof(struct free_block));
current->next = new_next; // We want to reach the next free block from the allocated block current->next = new_next; // We want to reach the next free block from the allocated block
current->size = req_size; current->size = rreq_size;
// Next-fit // Next-fit
this->free_start = new_next; this->free_start = new_next;
kout << " - Allocated " << hex << req_size << " Bytes with cutting" << endl; kout << " - Allocated " << hex << rreq_size << " Bytes with cutting" << endl;
} else { } else {
// Block too small to be cut, allocate whole block // Block too small to be cut, allocate whole block

7
c_os/user/HeapDemo.cc
View File

@ -30,6 +30,13 @@ void heap_demo() {
/* hier muss Code eingefuegt werden */ /* hier muss Code eingefuegt werden */
allocator.dump_free_memory(); allocator.dump_free_memory();
// Rounding to word border
kout << "ROUNDING ====================================================================" << endl;
void* alloc = allocator.alloc(1);
allocator.dump_free_memory();
allocator.free(alloc);
allocator.dump_free_memory();
// Some objects and forward/backward merging // Some objects and forward/backward merging
kout << "SOME OBJECTS ================================================================" << endl; kout << "SOME OBJECTS ================================================================" << endl;
MyObj* a = new MyObj(5); MyObj* a = new MyObj(5);