Merge branch 'feature/dynamic-control-size' into 'idf'

tlsf: allow each heap to have different control block See merge request espressif/tlsf!4
2025-11-16 12:34:46 +00:00 · 2022-10-25 13:19:48 +08:00
parent ab17d6798d 1ca1da2407
commit 13da0fff7f
3 changed files with 182 additions and 108 deletions
--- a/tlsf.c
+++ b/tlsf.c
@@ -215,12 +215,6 @@ tlsf_static_assert(sizeof(int) * CHAR_BIT == 32);
 tlsf_static_assert(sizeof(size_t) * CHAR_BIT >= 32);
 tlsf_static_assert(sizeof(size_t) * CHAR_BIT <= 64);

-/* SL_INDEX_COUNT must be <= number of bits in sl_bitmap's storage type. */
-tlsf_static_assert(sizeof(unsigned int) * CHAR_BIT >= SL_INDEX_COUNT);
-
-/* Ensure we've properly tuned our sizes. */
-tlsf_static_assert(ALIGN_SIZE == SMALL_BLOCK_SIZE / SL_INDEX_COUNT);
-
 static inline __attribute__((always_inline)) size_t align_up(size_t x, size_t align)
 {
 	tlsf_assert(0 == (align & (align - 1)) && "must align to a power of two");
@@ -245,7 +239,7 @@ static inline __attribute__((always_inline)) void* align_ptr(const void* ptr, si
 ** Adjust an allocation size to be aligned to word size, and no smaller
 ** than internal minimum.
 */
-static inline __attribute__((always_inline)) size_t adjust_request_size(size_t size, size_t align)
+static inline __attribute__((always_inline)) size_t adjust_request_size(tlsf_t tlsf, size_t size, size_t align)
 {
 	size_t adjust = 0;
 	if (size)
@@ -253,7 +247,7 @@ static inline __attribute__((always_inline)) size_t adjust_request_size(size_t s
 		const size_t aligned = align_up(size, align);

 		/* aligned sized must not exceed block_size_max or we'll go out of bounds on sl_bitmap */
-		if (aligned < block_size_max) 
+		if (aligned < tlsf_block_size_max(tlsf)) 
 		{
 			adjust = tlsf_max(aligned, block_size_min);
 		}
@@ -266,34 +260,34 @@ static inline __attribute__((always_inline)) size_t adjust_request_size(size_t s
 ** the documentation found in the white paper.
 */

-static inline __attribute__((always_inline)) void mapping_insert(size_t size, int* fli, int* sli)
+static inline __attribute__((always_inline)) void mapping_insert(control_t* control, size_t size, int* fli, int* sli)
 {
 	int fl, sl;
-	if (size < SMALL_BLOCK_SIZE)
+	if (size < control->small_block_size)
 	{
 		/* Store small blocks in first list. */
 		fl = 0;
-		sl = tlsf_cast(int, size) / (SMALL_BLOCK_SIZE / SL_INDEX_COUNT);
+		sl = tlsf_cast(int, size) / (control->small_block_size / control->sl_index_count);
 	}
 	else
 	{
 		fl = tlsf_fls_sizet(size);
-		sl = tlsf_cast(int, size >> (fl - SL_INDEX_COUNT_LOG2)) ^ (1 << SL_INDEX_COUNT_LOG2);
-		fl -= (FL_INDEX_SHIFT - 1);
+		sl = tlsf_cast(int, size >> (fl - control->sl_index_count_log2)) ^ (1 << control->sl_index_count_log2);
+		fl -= (control->fl_index_shift - 1);
 	}
 	*fli = fl;
 	*sli = sl;
 }

 /* This version rounds up to the next block size (for allocations) */
-static inline __attribute__((always_inline)) void mapping_search(size_t size, int* fli, int* sli)
+static inline __attribute__((always_inline)) void mapping_search(control_t* control, size_t size, int* fli, int* sli)
 {
-	if (size >= SMALL_BLOCK_SIZE)
+	if (size >= control->small_block_size)
 	{
-		const size_t round = (1 << (tlsf_fls_sizet(size) - SL_INDEX_COUNT_LOG2)) - 1;
+		const size_t round = (1 << (tlsf_fls_sizet(size) - control->sl_index_count_log2)) - 1;
 		size += round;
 	}
-	mapping_insert(size, fli, sli);
+	mapping_insert(control, size, fli, sli);
 }

 static inline __attribute__((always_inline)) block_header_t* search_suitable_block(control_t* control, int* fli, int* sli)
@@ -325,7 +319,7 @@ static inline __attribute__((always_inline)) block_header_t* search_suitable_blo
 	*sli = sl;

 	/* Return the first block in the free list. */
-	return control->blocks[fl][sl];
+	return control->blocks[fl * control->sl_index_count + sl];
 }

 /* Remove a free block from the free list.*/
@@ -339,9 +333,9 @@ static inline __attribute__((always_inline)) void remove_free_block(control_t* c
 	prev->next_free = next;

 	/* If this block is the head of the free list, set new head. */
-	if (control->blocks[fl][sl] == block)
+	if (control->blocks[fl * control->sl_index_count + sl] == block)
 	{
-		control->blocks[fl][sl] = next;
+		control->blocks[fl * control->sl_index_count + sl] = next;

 		/* If the new head is null, clear the bitmap. */
 		if (next == &control->block_null)
@@ -360,7 +354,7 @@ static inline __attribute__((always_inline)) void remove_free_block(control_t* c
 /* Insert a free block into the free block list. */
 static inline __attribute__((always_inline)) void insert_free_block(control_t* control, block_header_t* block, int fl, int sl)
 {
-	block_header_t* current = control->blocks[fl][sl];
+	block_header_t* current = control->blocks[fl * control->sl_index_count + sl];
 	tlsf_assert(current && "free list cannot have a null entry");
 	tlsf_assert(block && "cannot insert a null entry into the free list");
 	block->next_free = current;
@@ -373,7 +367,7 @@ static inline __attribute__((always_inline)) void insert_free_block(control_t* c
 	** Insert the new block at the head of the list, and mark the first-
 	** and second-level bitmaps appropriately.
 	*/
-	control->blocks[fl][sl] = block;
+	control->blocks[fl * control->sl_index_count + sl] = block;
 	control->fl_bitmap |= (1U << fl);
 	control->sl_bitmap[fl] |= (1U << sl);
 }
@@ -382,7 +376,7 @@ static inline __attribute__((always_inline)) void insert_free_block(control_t* c
 static inline __attribute__((always_inline)) void block_remove(control_t* control, block_header_t* block)
 {
 	int fl, sl;
-	mapping_insert(block_size(block), &fl, &sl);
+	mapping_insert(control, block_size(block), &fl, &sl);
 	remove_free_block(control, block, fl, sl);
 }

@@ -390,7 +384,7 @@ static inline __attribute__((always_inline)) void block_remove(control_t* contro
 static inline __attribute__((always_inline)) void block_insert(control_t* control, block_header_t* block)
 {
 	int fl, sl;
-	mapping_insert(block_size(block), &fl, &sl);
+	mapping_insert(control, block_size(block), &fl, &sl);
 	insert_free_block(control, block, fl, sl);
 }

@@ -553,7 +547,7 @@ static inline __attribute__((always_inline)) block_header_t* block_locate_free(c

 	if (size)
 	{
-		mapping_search(size, &fl, &sl);
+		mapping_search(control, size, &fl, &sl);
 		
 		/*
 		** mapping_search can futz with the size, so for excessively large sizes it can sometimes wind up 
@@ -561,7 +555,7 @@ static inline __attribute__((always_inline)) block_header_t* block_locate_free(c
 		** So, we protect against that here, since this is the only callsite of mapping_search.
 		** Note that we don't need to check sl, since it comes from a modulo operation that guarantees it's always in range.
 		*/
-		if (fl < FL_INDEX_COUNT)
+		if (fl < control->fl_index_count)
 		{
 			block = search_suitable_block(control, &fl, &sl);
 		}
@@ -590,22 +584,67 @@ static inline __attribute__((always_inline)) void* block_prepare_used(control_t*
 }

 /* Clear structure and point all empty lists at the null block. */
-static void control_construct(control_t* control)
+static control_t* control_construct(control_t* control, size_t bytes)
 {
-	int i, j;
+	// check that the requested size can at least hold the control_t. This will allow us 
+	// to fill in the field of control_t necessary to determine the final size of 
+	// the metadata overhead and check that the requested size can hold
+	// this data and at least a block of minimum size
+	if (bytes < sizeof(control_t))
+	{
+		return NULL;
+	}
+
+	/* Find the closest power of two for first layer */
+	control->fl_index_max = 32 - __builtin_clz(bytes);
+
+	/* Adapt second layer to the pool */
+	if (bytes <= 16 * 1024) control->sl_index_count_log2 = 3;
+	else if (bytes <= 256 * 1024) control->sl_index_count_log2 = 4;
+	else control->sl_index_count_log2 = 5;
+
+	control->fl_index_shift = (control->sl_index_count_log2 + ALIGN_SIZE_LOG2);
+	control->sl_index_count = 1 << control->sl_index_count_log2;
+	control->fl_index_count = control->fl_index_max - control->fl_index_shift + 1;
+	control->small_block_size = 1 << control->fl_index_shift;
+	
+	// the total size fo the metadata overhead is the size of the control_t
+	// added to the size of the sl_bitmaps and the size of blocks
+	control->size = sizeof(control_t) + (sizeof(*control->sl_bitmap) * control->fl_index_count) +
+										(sizeof(*control->blocks) * (control->fl_index_count * control->sl_index_count));
+
+	// check that the requested size can hold the whole control structure and
+	// a small block at least
+	if (bytes < control->size + block_size_min)
+	{
+		return NULL;
+	}

 	control->block_null.next_free = &control->block_null;
 	control->block_null.prev_free = &control->block_null;

 	control->fl_bitmap = 0;
-	for (i = 0; i < FL_INDEX_COUNT; ++i)
+	control->sl_bitmap = align_ptr(control + 1, sizeof(*control->sl_bitmap));
+	control->blocks = align_ptr(control->sl_bitmap + control->fl_index_count, sizeof(*control->blocks));
+
+
+	/* SL_INDEX_COUNT must be <= number of bits in sl_bitmap's storage type. */
+	tlsf_assert(sizeof(unsigned int) * CHAR_BIT >= control->sl_index_count
+		&& "CHAR_BIT less than sl_index_count");
+
+	/* Ensure we've properly tuned our sizes. */
+	tlsf_assert(ALIGN_SIZE == control->small_block_size / control->sl_index_count); //ALIGN_SIZE does not match");
+
+	for (int i = 0; i < control->fl_index_count; ++i)
 	{
 		control->sl_bitmap[i] = 0;
-		for (j = 0; j < SL_INDEX_COUNT; ++j)
+		for (int j = 0; j < control->sl_index_count; ++j)
 		{
-			control->blocks[i][j] = &control->block_null;
+			control->blocks[i * control->sl_index_count + j] = &control->block_null;
 		}
 	}
+
+	return control;
 }

 /*
@@ -645,14 +684,14 @@ int tlsf_check(tlsf_t tlsf)
 	int status = 0;

 	/* Check that the free lists and bitmaps are accurate. */
-	for (i = 0; i < FL_INDEX_COUNT; ++i)
+	for (i = 0; i < control->fl_index_count; ++i)
 	{
-		for (j = 0; j < SL_INDEX_COUNT; ++j)
+		for (j = 0; j < control->sl_index_count; ++j)
 		{
 			const int fl_map = control->fl_bitmap & (1U << i);
 			const int sl_list = control->sl_bitmap[i];
 			const int sl_map = sl_list & (1U << j);
-			const block_header_t* block = control->blocks[i][j];
+			const block_header_t* block = control->blocks[i * control->sl_index_count + j];

 			/* Check that first- and second-level lists agree. */
 			if (!fl_map)
@@ -680,7 +719,7 @@ int tlsf_check(tlsf_t tlsf)
 				tlsf_insist(block_is_prev_free(block_next(block)) && "block should be free");
 				tlsf_insist(block_size(block) >= block_size_min && "block not minimum size");

-				mapping_insert(block_size(block), &fli, &sli);
+				mapping_insert(control, block_size(block), &fli, &sli);
 				tlsf_insist(fli == i && sli == j && "block size indexed in wrong list");

 				if (tlsf_check_hook != NULL)
@@ -753,13 +792,32 @@ int tlsf_check_pool(pool_t pool)
 	return integ.status;
 }

+size_t tlsf_fit_size(tlsf_t tlsf, size_t size)
+{
+	/* because it's GoodFit, allocable size is one range lower */
+	if (size && tlsf != NULL) 
+	{
+		size_t sl_interval;
+		control_t* control = tlsf_cast(control_t*, tlsf);
+		sl_interval = (1 << (32 - __builtin_clz(size) - 1)) / control->sl_index_count;
+		return size & ~(sl_interval - 1);
+	}
+
+	return 0;
+}   
+
 /*
 ** Size of the TLSF structures in a given memory block passed to
 ** tlsf_create, equal to the size of a control_t
 */
-size_t tlsf_size(void)
+size_t tlsf_size(tlsf_t tlsf)
 {
-	return sizeof(control_t);
+	if (tlsf == NULL)
+	{
+		return 0;
+	}
+	control_t* control = tlsf_cast(control_t*, tlsf);
+	return control->size;
 }

 size_t tlsf_align_size(void)
@@ -772,9 +830,14 @@ size_t tlsf_block_size_min(void)
 	return block_size_min;
 }

-size_t tlsf_block_size_max(void)
+size_t tlsf_block_size_max(tlsf_t tlsf)
 {
-	return block_size_max;
+	if (tlsf == NULL)
+	{
+		return 0;
+	}
+	control_t* control = tlsf_cast(control_t*, tlsf);
+	return tlsf_cast(size_t, 1) << control->fl_index_max;
 }

 /*
@@ -807,16 +870,16 @@ pool_t tlsf_add_pool(tlsf_t tlsf, void* mem, size_t bytes)
 		return 0;
 	}

-	if (pool_bytes < block_size_min || pool_bytes > block_size_max)
+	if (pool_bytes < block_size_min || pool_bytes > tlsf_block_size_max(tlsf))
 	{
 #if defined (TLSF_64BIT)
 		printf("tlsf_add_pool: Memory size must be between 0x%x and 0x%x00 bytes.\n", 
 			(unsigned int)(pool_overhead + block_size_min),
-			(unsigned int)((pool_overhead + block_size_max) / 256));
+			(unsigned int)((pool_overhead + tlsf_block_size_max(tlsf)) / 256));
 #else
 		printf("tlsf_add_pool: Memory size must be between %u and %u bytes.\n", 
 			(unsigned int)(pool_overhead + block_size_min),
-			(unsigned int)(pool_overhead + block_size_max));
+			(unsigned int)(pool_overhead + tlsf_block_size_max(tlsf)));
 #endif
 		return 0;
 	}
@@ -852,7 +915,7 @@ void tlsf_remove_pool(tlsf_t tlsf, pool_t pool)
 	tlsf_assert(!block_is_free(block_next(block)) && "next block should not be free");
 	tlsf_assert(block_size(block_next(block)) == 0 && "next block size should be zero");

-	mapping_insert(block_size(block), &fl, &sl);
+	mapping_insert(control, block_size(block), &fl, &sl);
 	remove_free_block(control, block, fl, sl);
 }

@@ -888,31 +951,38 @@ int test_ffs_fls()
 }
 #endif

-tlsf_t tlsf_create(void* mem)
+tlsf_t tlsf_create(void* mem, size_t max_bytes)
 {
 #if _DEBUG
 	if (test_ffs_fls())
 	{
-		return 0;
+		return NULL;
 	}
 #endif

+	if (mem == NULL)
+	{
+		return NULL;
+	}
+
 	if (((tlsfptr_t)mem % ALIGN_SIZE) != 0)
 	{
 		printf("tlsf_create: Memory must be aligned to %u bytes.\n",
 			(unsigned int)ALIGN_SIZE);
-		return 0;
+		return NULL;
 	}

-	control_construct(tlsf_cast(control_t*, mem));
-
-	return tlsf_cast(tlsf_t, mem);
+	control_t* control_ptr = control_construct(tlsf_cast(control_t*, mem), max_bytes);
+	return tlsf_cast(tlsf_t, control_ptr);
 }

-tlsf_t tlsf_create_with_pool(void* mem, size_t bytes)
+tlsf_t tlsf_create_with_pool(void* mem, size_t pool_bytes, size_t max_bytes)
 {
-	tlsf_t tlsf = tlsf_create(mem);
-	tlsf_add_pool(tlsf, (char*)mem + tlsf_size(), bytes - tlsf_size());
+	tlsf_t tlsf = tlsf_create(mem, max_bytes ? max_bytes : pool_bytes);
+	if (tlsf != NULL)
+	{
+		tlsf_add_pool(tlsf, (char*)mem + tlsf_size(tlsf), pool_bytes - tlsf_size(tlsf));
+	}
 	return tlsf;
 }

@@ -924,13 +994,13 @@ void tlsf_destroy(tlsf_t tlsf)

 pool_t tlsf_get_pool(tlsf_t tlsf)
 {
-	return tlsf_cast(pool_t, (char*)tlsf + tlsf_size());
+	return tlsf_cast(pool_t, (char*)tlsf + tlsf_size(tlsf));
 }

 void* tlsf_malloc(tlsf_t tlsf, size_t size)
 {
 	control_t* control = tlsf_cast(control_t*, tlsf);
-	const size_t adjust = adjust_request_size(size, ALIGN_SIZE);
+	const size_t adjust = adjust_request_size(tlsf, size, ALIGN_SIZE);
 	block_header_t* block = block_locate_free(control, adjust);
 	return block_prepare_used(control, block, adjust);
 }
@@ -961,7 +1031,7 @@ void* tlsf_malloc(tlsf_t tlsf, size_t size)
 void* tlsf_memalign_offs(tlsf_t tlsf, size_t align, size_t size, size_t data_offset)
 {
 	control_t* control = tlsf_cast(control_t*, tlsf);
-	const size_t adjust = adjust_request_size(size, ALIGN_SIZE);
+	const size_t adjust = adjust_request_size(tlsf, size, ALIGN_SIZE);
 	const size_t off_adjust = align_up(data_offset, ALIGN_SIZE);

 	/*
@@ -976,7 +1046,7 @@ void* tlsf_memalign_offs(tlsf_t tlsf, size_t align, size_t size, size_t data_off
 	/* The offset is included in both `adjust` and `gap_minimum`, so we
 	** need to subtract it once.
 	*/
-	const size_t size_with_gap = adjust_request_size(adjust + align + gap_minimum - off_adjust, align);
+	const size_t size_with_gap = adjust_request_size(tlsf, adjust + align + gap_minimum - off_adjust, align);

 	/*
 	** If alignment is less than or equal to base alignment, we're done, because
@@ -1089,7 +1159,13 @@ void* tlsf_realloc(tlsf_t tlsf, void* ptr, size_t size)

 		const size_t cursize = block_size(block);
 		const size_t combined = cursize + block_size(next) + block_header_overhead;
-		const size_t adjust = adjust_request_size(size, ALIGN_SIZE);
+		const size_t adjust = adjust_request_size(tlsf, size, ALIGN_SIZE);
+
+		// if adjust if equal to 0, the size is too big
+		if (adjust == 0)
+		{
+			return p;
+		}

 		tlsf_assert(!block_is_free(block) && "block already marked as free");

--- a/tlsf.h
+++ b/tlsf.h
@@ -20,8 +20,8 @@ typedef void* tlsf_t;
 typedef void* pool_t;

 /* Create/destroy a memory pool. */
-tlsf_t tlsf_create(void* mem);
-tlsf_t tlsf_create_with_pool(void* mem, size_t bytes);
+tlsf_t tlsf_create(void* mem, size_t max_bytes);
+tlsf_t tlsf_create_with_pool(void* mem, size_t pool_bytes, size_t max_bytes);
 void tlsf_destroy(tlsf_t tlsf);
 pool_t tlsf_get_pool(tlsf_t tlsf);

@@ -40,13 +40,23 @@ void tlsf_free(tlsf_t tlsf, void* ptr);
 size_t tlsf_block_size(void* ptr);

 /* Overheads/limits of internal structures. */
-size_t tlsf_size(void);
+size_t tlsf_size(tlsf_t tlsf);
 size_t tlsf_align_size(void);
 size_t tlsf_block_size_min(void);
-size_t tlsf_block_size_max(void);
+size_t tlsf_block_size_max(tlsf_t tlsf);
 size_t tlsf_pool_overhead(void);
 size_t tlsf_alloc_overhead(void);

+/**
+ * @brief Return the allocable size based on the size passed
+ * as parameter
+ * 
+ * @param tlsf Pointer to the tlsf structure
+ * @param size The allocation size
+ * @return size_t The updated allocation size
+ */
+size_t tlsf_fit_size(tlsf_t tlsf, size_t size);
+
 /* Debugging. */
 typedef void (*tlsf_walker)(void* ptr, size_t size, int used, void* user);
 void tlsf_walk_pool(pool_t pool, tlsf_walker walker, void* user);
--- a/tlsf_common.h
+++ b/tlsf_common.h
@@ -35,41 +35,9 @@ extern "C" {

 enum tlsf_config
 {
-	/* log2 of number of linear subdivisions of block sizes. Larger
-	** values require more memory in the control structure. Values of
-	** 4 or 5 are typical.
-	*/
-	SL_INDEX_COUNT_LOG2  = 5,
-
 	/* All allocation sizes and addresses are aligned to 4 bytes. */
 	ALIGN_SIZE_LOG2 = 2,
 	ALIGN_SIZE = (1 << ALIGN_SIZE_LOG2),
-
-	/*
-	** We support allocations of sizes up to (1 << FL_INDEX_MAX) bits.
-	** However, because we linearly subdivide the second-level lists, and
-	** our minimum size granularity is 4 bytes, it doesn't make sense to
-	** create first-level lists for sizes smaller than SL_INDEX_COUNT * 4,
-	** or (1 << (SL_INDEX_COUNT_LOG2 + 2)) bytes, as there we will be
-	** trying to split size ranges into more slots than we have available.
-	** Instead, we calculate the minimum threshold size, and place all
-	** blocks below that size into the 0th first-level list.
-	*/
-
-	/* Tunning the first level, we can reduce TLSF pool overhead
-	 * in exchange of manage a pool smaller than 4GB
-	 */
-	#ifdef FL_INDEX_MAX_PLATFORM
-	FL_INDEX_MAX = FL_INDEX_MAX_PLATFORM,
-	#else
-	FL_INDEX_MAX = 30,
-	#endif
-
-	SL_INDEX_COUNT = (1 << SL_INDEX_COUNT_LOG2),
-	FL_INDEX_SHIFT = (SL_INDEX_COUNT_LOG2 + ALIGN_SIZE_LOG2),
-	FL_INDEX_COUNT = (FL_INDEX_MAX - FL_INDEX_SHIFT + 1),
-
-	SMALL_BLOCK_SIZE = (1 << FL_INDEX_SHIFT),
 };

 /*
@@ -92,20 +60,6 @@ typedef struct block_header_t
 	struct block_header_t* prev_free;
 } block_header_t;

-/* The TLSF control structure. */
-typedef struct control_t
-{
-	/* Empty lists point at this block to indicate they are free. */
-	block_header_t block_null;
-
-	/* Bitmaps for free lists. */
-	unsigned int fl_bitmap;
-	unsigned int sl_bitmap[FL_INDEX_COUNT];
-
-	/* Head of free lists. */
-	block_header_t* blocks[FL_INDEX_COUNT][SL_INDEX_COUNT];
-} control_t;
-
 /*
 ** Since block sizes are always at least a multiple of 4, the two least
 ** significant bits of the size field are used to store the block status:
@@ -132,7 +86,41 @@ static const size_t block_start_offset =
 */
 static const size_t block_size_min = 
 	sizeof(block_header_t) - sizeof(block_header_t*);
-static const size_t block_size_max = tlsf_cast(size_t, 1) << FL_INDEX_MAX;
+
+/* The TLSF control structure. */
+typedef struct control_t
+{
+    /* Empty lists point at this block to indicate they are free. */
+    block_header_t block_null;
+
+    /* Local parameter for the pool. Given the maximum
+	 * value of each field, all the following parameters
+	 * can fit on 4 bytes when using bitfields
+	 */
+    unsigned int fl_index_count : 5; // 5 cumulated bits
+    unsigned int fl_index_shift : 3; // 8 cumulated bits
+    unsigned int fl_index_max : 6; // 14 cumulated bits
+    unsigned int sl_index_count : 6; // 20 cumulated bits
+
+	/* log2 of number of linear subdivisions of block sizes. Larger
+	** values require more memory in the control structure. Values of
+	** 4 or 5 are typical.
+	*/
+    unsigned int sl_index_count_log2 : 3; // 23 cumulated bits
+    unsigned int small_block_size : 8; // 31 cumulated bits
+
+	/* size of the metadata ( size of control block,
+	 * sl_bitmap and blocks )
+	 */
+    size_t size;
+
+    /* Bitmaps for free lists. */
+    unsigned int fl_bitmap;
+    unsigned int *sl_bitmap;
+
+    /* Head of free lists. */
+    block_header_t** blocks;
+} control_t;

 #if defined(__cplusplus)
 };