Re: freeing srcprops ?

[Han-Wen Nienhuys <hanwen@xs4all.nl>]

Neil Jerram escreveu:
>>>>> 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.

Any deviation from the standard memory allocation scheme should have a
good reason, or -at least- a documented reason.

This design predates several revisions of the garbage collector, so I
suspect that whatever reason there was for this idea, is no longer
valid.

>> on the factual side: 
>>
>> 1. the GUILE ends up with 1506 srcprops objects.
> 
> Out of interest, in what scenario?

Startup (with --debug), which you brought up earlier. As I indicated
in an earlier message, I did not see any measurable change in startup
time.

>> 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.)

That was not the point of the change.

>> 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.

I don't mind either, but since the old code was using a struct with
its own 'optimized' memory management scheme, I assumed that an even
better scheme (due to lower memory use) could not be questioned.

>> 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 

Can we have some measurable data?

Thanks,  

-- 
 Han-Wen Nienhuys - hanwen@xs4all.nl - http://www.xs4all.nl/~hanwen



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