Han-Wen Nienhuys <[EMAIL PROTECTED]> writes:
> Neil Jerram escreveu:
>> Kevin Ryde <[EMAIL PROTECTED]> writes:
>>
>>> Han-Wen Nienhuys <[EMAIL PROTECTED]> writes:
>>>> why use a separate storage pool for srcprop objects?
>>> At a guess, is it because that they're likely to never need freeing,
>>> hence can be laid down in big blocks.
>>
>> I'd guess because setting up a srcprops is critical to start-up
>> performance, and a double cell doesn't have enough slots to store all
>> the common properties (filename, pos, copy) directly (as your change
>> makes clear).
>
> All this guessing ... I suspect it was done just because of poor design
> and/or premature optimization.
Except you haven't given any objective reasons for why the design is
poor or the optimization premature.
> on the factual side:
>
> 1. the GUILE ends up with 1506 srcprops objects.
Out of interest, in what scenario?
> 2. this is neglible compared to the 431777 total cells that
> are allocated.
(Which suggests to me that the decrease in memory from your change
wasn't that worthwhile.)
> 3. Due to sharing of the filename cons, memory usage is slightly more
> than 4 SCMs per srcprop, down from 6 SCMs (2 for the smob cell, 4 for the
> struct)
Well that's nice, but only to be expected from throwing away a
performance/occupancy optimization.
> I actually think it would be a good idea to generalize from double cells,
> to cells containing any number between 3 and 8 SCM values. This would
> be a better fit with some datatypes, and obviates the procustes
> hacking to fit all the information inside some struct.
Maybe. I think this would have to be motivated by looking at
particular cases where we get benefits from moving struct data into a
multiple cell. I don't think the srcprops case is clearcut
(obviously), and I don't see anything wrong with the general approach
of indirecting to a struct.
> Because the code made me cringe. It's pointless to have specialized storage
> for srcprops. it only makes the code more obtuse.
I disagree. I believe there was point to the code, and it was nowhere
near obtuse.
> I you really want to know, ask Mikael Djurfeldt who added the bits
> in 20 aug 1996.
I don't think I need to. Mikael was responsible for adding all
Guile's low-level debugging support, including this. He took great
care to minimize the impact of this support on runtime performance -
which it seems to me that you are now throwing away because "the code
makes you cringe".
Regards,
Neil
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