Mac: LuxRender slow down at start

[joedepas]

I use LuxRender 0.9 only with Reality2 plugin for Daz Studio4 (Reality2 update 2.20.1.115).
I have an iMac 24" Intel Core 2 duo with 4Gb Ram and an ATI Radeon HD4850 graphic card, with OS 10.6.8. I never use GPU acceleration with LuxRender as it seems it is not supported by my graphic card.
When I started using LuxRender, about two months ago, everything seemed to work fine, so I didn't pay much attention to the parameters. Rendering times were long (from 12 to 20 hours for a final render, depending on the complexity of the scene and the lighting) but on the whole acceptable, and the results quite fine. Above all, I was able to judge if the render conformed my expectations just after 10÷15 minutes from its start.
After a while I had a dramatic slow down in render times: I can't say if I made something wrong without being aware, however was not able to put things back in the proper way, not even reinstalling LuxRender and Reality from scratch.
So I started making some experiments step by step, registering all the statistic parameters, especially kC/s. I noticed than, whilst before the slow down the resource allocation was very quick and after starting the render LuxRender got the standard kC/s almost immediately, now the time of the resource allocation was much longer (the computer seems to «suffer» for some time, using all its resources to get the render start), and the render always started with something about 100 C/s (note: C/s, not kC/s), improving progressively but slowly in a very long time.
Next step I downloaded 5741_luxrender_osx64_1-19-2011 (but it was january 2012!) version, installed it (before I used the standard version LuxRender_0.9dev_universal), and things changed: not perfect, but much better. LuxRender still starts very slowly, beginning with 300÷500 C/s, however this 64 bit version speeds up progressively and in about an hour it reaches a reasonable speed. Look at the resume hereafter:
after 30': 30kC/s and 6 S/p
after 1h: 53 kC/s and 20 S/p
after 2h: 68 kC/s and 50 S/p
after 3h: 74 kC/s and 82 S/p
regimen: 80kC/s and about 30 S/p per hour
Ultimately, I could be quite satisfied with these render times, which are almost the same I had for my renders before the slow down crisis. There is still a problem: now I have to wait from 30 minutes to 1h to possibly judge if the render conforms to my expectations. Moreover, not always things are so easy, depending on the lighting: sometimes the slow down comes back, especially if I try to adjust the lighting settings during the render.
So, if anyone has any idea and/or suggestion about this problem, its origin and how to solve it, he is welcome. If you need more info, just ask. As I said, I always use LuxRender in the simplest way (no GPU, no memory conservation, only render frame). Thanks for your time.

[J the Ninja]

It sounds almost like Lux is running out of memory and forcing the OS to swap a bunch of stuff out before it can fit everything in RAM and get going properly. Possible you've been doing more complex scenes as of late? Can you check things in activity monitor, under the Memory tab, look at the "Free" value. Does it go down very low (under 50MB or so, or even less) when Lux is getting going? If so, memory is your issue. You could try upgrading it if you want (I believe your machine will support 2x4GB, check http://www.macsales.com), or just quit a few apps before starting the render. (or do simpler scenes)

You could also try the "memory conservative" option Reality has, although tbh I have no clue what it does, Lux doesn't have any option that could correspond to directly.

[joedepas]

It sounds almost like Lux is running out of memory and forcing the OS to swap a bunch of stuff out before it can fit everything in RAM and get going properly. Possible you've been doing more complex scenes as of late? Can you check things in activity monitor, under the Memory tab, look at the "Free" value. Does it go down very low (under 50MB or so, or even less) when Lux is getting going? If so, memory is your issue. You could try upgrading it if you want (I believe your machine will support 2x4GB, check http://www.macsales.com), or just quit a few apps before starting the render. (or do simpler scenes)

You could also try the "memory conservative" option Reality has, although tbh I have no clue what it does, Lux doesn't have any option that could correspond to directly.

Thank you for answering: it seems to me too that there is a problem of memory in allocating computer resources. It is not a question of scene or lighting complexity, because I tried to render again the same scene I had rendered with Luxrender before the slow down in 20 hours, and things were much worse (I gave up after 2 hours, 'cause now it seemed to require more than 200 hours to get 500 S/p). I made tests using LuxRender as the only program running on my Mac, which – by the way – is working properly with every other app, including DazStudio4 and renders in 3Delight. I know I could increase the Ram, however I was quite satisfied with things as they were before. The «memory conservative» option makes things worse, as it allows less memory to be used by LuxRender, so I don't check it in Reality. I'll try to check the Memory tab while using LuxRender, to see the value.
I have one more question: in Snow Leopard, are there other files related to LuxRender in addition to its folder in Applications and the preference file in Username>Library>Preferences?

[joedepas]

Free memory is low, between 12 and 20 MB. However there are 1.24 GB of inactive memory. The real memory required by LuxRender is about 3.15 MB (4 GB with the virtual memory). I don't understand what is that inactive memory (blue color). Any advice?

[Dade]

Do you have any surface subdivision active ? It is very easy to eat tons of ram by setting a too high surface subdivision.

[SATtva]

The same goes for Fireflies Rejection feature of Lux -- it consumes quite a lot of RAM with high settings.

[joedepas]

It is a Ram problem for sure: when I quit all other apps, free memory goes over 60 MB and LuxRender works better. So I'm going to buy 8GB of Ram.
Still I wonder why things were far better before the slow down...