"""
Memory comparision of obmalloc arena/pool schemes.

SQ is the status quo:  we have to use four separate 4 KiB pools, and
each burns 48 bytes for a pool header.

PR:  Tim's PR.  There's one pool spanning 4 pages, with 48 bytes for a
pool header in the first page, and 16 bytes to store the arena index
in each of the other 3 pages.

RT:  the radix tree.  One 16 KiB block that only "wastes" 48 bytes for
the pool header.
"""

PAGES_PER_POOL = 4
ALIGNMENT = 16  # change to 8 for < Python 3.8

PAGE_SIZE = 2 ** 12
POOL_SIZE = PAGE_SIZE * PAGES_PER_POOL
POOL_HEADER_SIZE = 48


def from_block(size, blocksize, overhead):
    return (blocksize - overhead) // size


def from_first_page(size, *, pagesize=PAGE_SIZE):
    return from_block(size, pagesize, POOL_HEADER_SIZE)


# using multiple 4K one-page pools - status quo
def nobj_4K(size):
    return from_first_page(size) * PAGES_PER_POOL


# using the PR
def nobj_PR(size):
    return from_first_page(size) + from_block(size, PAGE_SIZE, ALIGNMENT) * (
        PAGES_PER_POOL - 1
    )


# using the radix tree branch
def nobj_RT(size):
    return from_first_page(size, pagesize=POOL_SIZE)


print("pages per pool", PAGES_PER_POOL)
print(f"pool size {POOL_SIZE:,}")
print("alignment", ALIGNMENT)

for size in range(ALIGNMENT, 512 + 1, ALIGNMENT):
    print("size", size)
    for tag, f in (("SQ", nobj_4K), ("PR", nobj_PR), ("RT", nobj_RT)):
        nobj = f(size)
        waste = POOL_SIZE - nobj * size
        print(f"    {tag} {nobj:4} {waste/POOL_SIZE:5.1%}")