[bug][mono] sgen alloc nursery heap size

[srxqds]

I have set nursery size use nursery-size=8m.

it will call alloc_nursery pass dynamic_nursery: false min_nursery_size: 8388608(8m), max_nursery_size : 8388608(8m)

runtime/src/mono/mono/sgen/sgen-gc.c

Line 3708 in 6d5f8e4

alloc_nursery (dynamic_nursery, min_nursery_size, max_nursery_size);

and then:

runtime/src/mono/mono/sgen/sgen-gc.c

Lines 1047 to 1050 in 6d5f8e4

	* sgen_nursery_size <= sgen_nursery_section size <= sgen_nursery_max_size
	*/
	data = (char *)sgen_major_collector.alloc_heap (max_size, max_size);
	sgen_update_heap_boundaries ((mword)data, (mword)(data + max_size));

add last call mono_valloc_aligned, will add size + aligned leading the size to 16m at line 165:

runtime/src/mono/mono/utils/mono-mmap-wasm.c

Lines 158 to 171 in 34e64ad

	mono_valloc_aligned (size_t size, size_t alignment, int flags, MonoMemAccountType type)
	{
	// We don't need padding if the alignment is compatible with the page size
	if (mono_opt_wasm_mmap && ((MWPM_PAGE_SIZE % alignment) == 0))
	return valloc_impl (NULL, size, flags, type);
	/* Allocate twice the memory to be able to put the block on an aligned address */
	char *mem = (char *) valloc_impl (NULL, size + alignment, flags, type);
	char *aligned;
	if (!mem)
	return NULL;
	aligned = mono_aligned_address (mem, size, alignment);

[srxqds]

It cause memory waste?

[srxqds]

why need alloc double memory size, anyone can check it?

[steveisok]

@kg @lateralusX @BrzVlad any of you know the answer to @srxqds question?