// from the result if we have one, since mallocgc will add it back in.
		if reqSize <= smallSizeMax-8 {
			return uintptr(class_to_size[size_to_class8[divRoundUp(reqSize, smallSizeDiv)]]) - (reqSize - size)
		}
		return uintptr(class_to_size[size_to_class128[divRoundUp(reqSize-smallSizeMax, largeSizeDiv)]]) - (reqSize - size)
	}
	// Large object. Align reqSize up to the next page. Check for overflow.
	reqSize += pageSize - 1