[plt-scheme] cost of closure?

On 5/31/07, Matthew Flatt <mflatt at cs.utah.edu> wrote:
> At Thu, 31 May 2007 21:01:12 -0500, "Robby Findler" wrote:
> > When I run the below I get 42.2 bytes (on average) for 1 cons and 1
> > 3-var closure, as compared to 13.76 bytes (on average) for 1 cons and
> > one struct. This is according to current-memory-use.
>
> It would be really cool if a 3-value struct plus a cons cell added up
> 14 bytes! Unfortunately, the run-time system isn't that clever...
>
> 100 objects is too small to measure via `current-memory-use'. I turned
> up `num' to 100000, and I get right at 40 bytes in both cases. That's
> the answer I expect, based on the implementation:
>
>    12 = 4 bytes * 3 fields or captured bindings
>     4 = 4 bytes * 1 code (closure) or type (struct) pointer
>     4 = 4 bytes * 1 MzScheme type tag and hash code
>    12 = 12 bytes per cons cell (MzScheme level)
>     8 = 4 bytes * 2 objects for GC's layer of size info
>  ----
>    40
>
> Add a little bit of page-level GC management overhead, and the result
> should be slightly more than 40 bytes per.

Ah, thanks for clarifying. Makes me wonder if my earlier experiments
are bogus ...

Robby