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buddy.cpp
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buddy.cpp
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//File: buddy.cpp
#include <buddy.h>
#include <math.h>
#include <assert.h>
bool is_power_of_two(unsigned long x){
return ((x != 0) && !(x & (x - 1)));
}
unsigned long next_power_of_two(unsigned long n){
unsigned long p = 1;
if (is_power_of_two(n))
return n;
while (p < n) {
p <<= 1;
}
return p;
}
void set_bit(unsigned long bit, unsigned long* addr){
unsigned long mask = BIT_MASK(bit);
addr[BIT_WORD(bit)] |= mask;
}
void clear_bit(unsigned long bit, unsigned long* addr){
unsigned long mask = BIT_MASK(bit);
addr[BIT_WORD(bit)] &= ~mask;
}
bool test_bit(unsigned long bit, unsigned long* addr){
unsigned long mask = BIT_MASK(bit);
return (addr[BIT_WORD(bit)] & mask);
}
/**
* Converts a block address to its block index in the specified buddy allocator.
* A block's index is used to find the block's tag bit, buddy->tag_bits[block_id].
*/
unsigned long block_to_id(buddy_t *buddy, block_t *block){
unsigned int blk_size_order = MIN_ORDER_LOG;
unsigned long block_id = ((unsigned long)block - buddy->base_addr) >> blk_size_order;
assert(block_id < buddy->num_blocks);
return block_id;
}
buddy_t* buddy_init(void *space, unsigned int max_order){
buddy_t *buddy = (buddy_t*)space;
buddy->max_order = max_order;
buddy->num_blocks = pow(2,max_order);
buddy->mutexp = new((void*)(&buddy->mutex)) std::mutex();
buddy->available = (list_ctl_t*)((buddy_t*)space + 1);
buddy->tag_bits = (unsigned long*)(buddy->available + max_order + 1);
//unsigned long is 64 bit long which can track 64 blocks
//number of unsigned longs needed is equal to
// (buddy->num_blocks + 64 - 1) / 64
for(unsigned int i = 0; i < max_order + 1; i++){
list_init(&(buddy->available[i]));
}
//initially the bitmap says that all blocks are taken
for(unsigned int i=0; i < BITS_TO_LONGS(buddy->num_blocks); i++){
buddy->tag_bits[i] = 0;
}
//all blocks make up an entire group of free blocks
//and the first_block is linked to max_order list
buddy->base_addr = (unsigned long)(buddy->tag_bits + BITS_TO_LONGS(buddy->num_blocks));
buddy->base_addr += BLOCK_SIZE - 1;
buddy->base_addr &= ~(BLOCK_SIZE - 1);
block_t *first_block = (block_t*)buddy->base_addr;
first_block->order = max_order;
list_add(&buddy->available[max_order], &first_block->link);
return buddy;
}
void mark_allocated(buddy_t *buddy, block_t *block){
clear_bit(block_to_id(buddy, block), buddy->tag_bits);
}
void mark_available(buddy_t *buddy, block_t *block){
set_bit(block_to_id(buddy, block), buddy->tag_bits);
}
int is_available(buddy_t *buddy, block_t *block){
return test_bit(block_to_id(buddy, block), buddy->tag_bits);
}
void* find_buddy(buddy_t *buddy_alloc, block_t *block, unsigned int order){
unsigned long _block;
unsigned long _buddy;
assert((unsigned long)block >= buddy_alloc->base_addr);
if(order < 0) order = 0;
/* Make block address to be zero-relative */
_block = (unsigned long)block - buddy_alloc->base_addr;
/* Calculate buddy in zero-relative space */
unsigned long __buddy = 1UL << order;
_buddy = _block ^ (__buddy << (unsigned)MIN_ORDER_LOG);
/* Return the buddy's address */
return (void *)(_buddy + buddy_alloc->base_addr);
}
block_t* buddy_alloc(buddy_t *buddy, unsigned int order){
unsigned int j;
list_ctl_t *list;
block_t *block;
unsigned long buddy_block_num;
block_t *buddy_group_start_blk;
buddy->mutex.lock();
assert(buddy != nullptr);
if(order > buddy->max_order){
buddy->mutex.unlock();
return nullptr;
}
if(order < 0) order = 0;
for (j = order; j <= buddy->max_order; j++) {
/* Try to allocate the FIRST block in the order j list */
list = &buddy->available[j];
if (list_empty(list)) continue;
block = list_entry(list->next, block_t, link);
list_del_el(&block->link);
mark_allocated(buddy, block);
/* Divide if higher order block than necessary was allocated */
while (j > order) {
--j;
buddy_block_num = 1UL << j;
buddy_group_start_blk = (block_t *)((unsigned long)block + (buddy_block_num << (unsigned)MIN_ORDER_LOG));
buddy_group_start_blk->order = j;
mark_available(buddy, buddy_group_start_blk);
list_add(&buddy->available[j], &buddy_group_start_blk->link);
}
block->order = j;
buddy->mutex.unlock();
return block;
}
buddy->mutex.unlock();
return nullptr;
}
void buddy_free(buddy_t *buddy, void *addr, unsigned int order){
block_t* block = nullptr;
buddy->mutex.lock();
assert(buddy != nullptr);
assert(order <= buddy->max_order);
/* Fixup requested order to be at least the minimum supported */
if (order < 0)
order = 0;
/* Put block structure on the group being freed */
block = (block_t*) addr;
assert(!is_available(buddy, block));
/* Coalesce as much as possible with adjacent free buddy blocks */
while (order < buddy->max_order) {
/* Determine our buddy block's address */
block_t * buddy_group =(block_t*) find_buddy(buddy, block, order);
/* Make sure buddy is available and has the same size as us */
if (!is_available(buddy, buddy_group))
break;
if (is_available(buddy, buddy_group) && (buddy_group->order != order))
break;
/* buddy coalesce! */
list_del_el(&buddy_group->link);
if (buddy_group < block)
block = buddy_group;
++order;
block->order = order;
}
/* Add the (possibly coalesced) block to the appropriate free list */
block->order = order;
mark_available(buddy, block);
list_add(&buddy->available[order], &block->link);
buddy->mutex.unlock();
}
void buddy_allocator_log(buddy_t *buddy){
unsigned int i;
unsigned long num_groups;
list_ctl_t *entry;
buddy->mutex.lock();
printf("DUMP OF BUDDY MEMORY POOL:\n");
printf(" Area Order=%u\n",
buddy->max_order);
for (i = 0; i <= buddy->max_order; i++) {
/* Count the number of memory blocks in the list */
num_groups = 0;
list_for_each(entry, &buddy->available[i]){
if(!list_empty(&buddy->available[i])){
++num_groups;
}
}
if(num_groups == 1){
printf(" order %2u: %lu free group\n", i, num_groups);
}else{
printf(" order %2u: %lu free groups\n", i, num_groups);
}
}
buddy->mutex.unlock();
}