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lib/os/heap: minimize initial overallocation in the aligned case

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The biggest required padding is equal to `align - chunk_header_bytes`
and not `align - 1` given that the header already contributes to the
padding.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2020-10-23 17:45:46 -04:00 • committed by Anas Nashif
commit 9dcd76a650
2 changed files with 12 additions and 2 deletions
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3
lib/os/heap.c
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@ -261,7 +261,8 @@ void *sys_heap_aligned_alloc(struct sys_heap *heap, size_t align, size_t bytes)
* We over-allocate to account for alignment and then free
* the extra allocations afterwards.
*/
size_t padded_sz = bytes_to_chunksz(h, bytes + align - 1);
size_t padded_sz =
bytes_to_chunksz(h, bytes + align - chunk_header_bytes(h));
chunkid_t c0 = alloc_chunk(h, padded_sz);
if (c0 == 0) {

11
tests/lib/heap_align/src/main.c
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@ -60,7 +60,7 @@ static void check_heap_align(struct sys_heap *h,
static void test_aligned_alloc(void)
{
struct sys_heap heap = {};
void *p;
void *p, *q;
sys_heap_init(&heap, heapmem, HEAP_SZ);
@ -87,6 +87,15 @@ static void test_aligned_alloc(void)
memset(p, 0, 12);
zassert_true(sys_heap_validate(&heap), "heap invalid");
sys_heap_free(&heap, p);
/* corner case with minimizing the overallocation before alignment */
p = sys_heap_aligned_alloc(&heap, 16, 16);
q = sys_heap_aligned_alloc(&heap, 16, 17);
memset(p, 0, 16);
memset(q, 0, 17);
zassert_true(sys_heap_validate(&heap), "heap invalid");
sys_heap_free(&heap, p);
sys_heap_free(&heap, q);
}
void test_main(void)