apc_sma_info

The above example will output something similar to:

Array
(
    [num_seg] => 1
    [seg_size] => 31457280
    [avail_mem] => 31448408
    [block_lists] => Array
        (
            [0] => Array
                (
                    [0] => Array
                        (
                            [size] => 31448408
                            [offset] => 8864
                        )

                )

        )

)