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remove MI_ALIGNMENT_MAX and add comments

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daan 2022-11-07 11:13:42 -08:00
parent 711aad7a75
commit 1f12c3dd12
6 changed files with 16 additions and 17 deletions
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13
src/os.c
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@ -842,29 +842,30 @@ void* _mi_os_alloc_aligned(size_t size, size_t alignment, bool commit, bool* lar
/* -----------------------------------------------------------
OS aligned allocation with an offset. This is used
for large alignments > MI_SEGMENT_SIZE so we can align
the first page at an offset from the start of the segment.
As we may need to overallocate, we need to free such pointers
using `mi_free_aligned` to use the actual start of the
memory region.
for large alignments > MI_ALIGNMENT_MAX. We use a large mimalloc
page where the object can be aligned at an offset from the start of the segment.
As we may need to overallocate, we need to free such pointers using `mi_free_aligned`
to use the actual start of the memory region.
----------------------------------------------------------- */
void* _mi_os_alloc_aligned_offset(size_t size, size_t alignment, size_t offset, bool commit, bool* large, mi_stats_t* tld_stats) {
mi_assert(offset <= MI_SEGMENT_SIZE);
mi_assert(offset <= size);
mi_assert((alignment % _mi_os_page_size()) == 0);
if (offset > MI_SEGMENT_SIZE) return NULL;
if (offset == 0) {
// regular aligned allocation
return _mi_os_alloc_aligned(size, alignment, commit, large, tld_stats);
}
else {
// overallocate to align at an offset
const size_t extra = _mi_align_up(offset, alignment) - offset;
const size_t oversize = size + extra;
void* start = _mi_os_alloc_aligned(oversize, alignment, commit, large, tld_stats);
if (start == NULL) return NULL;
void* p = (uint8_t*)start + extra;
mi_assert(_mi_is_aligned((uint8_t*)p + offset, alignment));
// decommit the overallocation at the start
if (commit && extra > _mi_os_page_size()) {
_mi_os_decommit(start, extra, tld_stats);
}