Slow / no rendering when RAM usage is very high

[notamondayfan]

Hello,

Just something I hope someone might be able to give some guidance to.

I have a very RAM intensive scene (using forest pack pro for a rug) and when I come to render the image, the render is very slow, on both the local machine and on the DR nodes.

I'm guessing it's down to the scene using all the available RAM, and then caching to the scratch drive, but then it should render at 100% CPU power?


PC and rendernode


Buckets (or lack of)

Does anyone know if this is normal, and if so are there any work-arounds to get the scene rendering at full power without massively modifying the scene, or rendering with the rug hidden?

I've used this technique in the past, so I'm a bit stumped by why it's not working this time round.

Any help would be really appreciated!

Thanks,
Dean

[Neilg]

It is normal. if you run out of ram then you need to swap things in and out of memory - stopping the render in the process. you want to avoid this as much as possible.

In the render settings/settings tab, what is your 'dynamic memory limit' set to? I tend to go with 80% of the RAM in the machine. It defaults to 400mb, which is insane and about 15 years out of date.
e: maybe you've already put this up, nevermind.

If it's already as high as it can go then you'll need to simplify the rug or render as a pass. How much RAM does the scene use if you delete the rug from it? If it's already close to 16gb then you'll be better off optimizing the rest of the scene - it's pretty hard to say what you need to change without seeing it.

[notamondayfan]

I was fearful this would be the case. The scene is very simple, a sofa, some props, walls, floor, and 4 vray lights, nothing that should push up RAM anyway.

I'll look to simplify the sofa, but I wanted to push the detail on this one, and so I look to use Forest Pro. I'll post on their forum and see what they say too.

Cheers,
Dean

[Neilg]

delete the rug and show us what the RAM usage is.

Theres something seriously wrong with the way you've got forest set up if it can eat through 14+ gb of ram by itself, that's insane. Would you be able to upload the rug in it's own scene?

[notamondayfan]

I think it's because I've made the rug from individual strands, rather than clumps, so I have literally millions of rug strands. I'm guessing Forest / Max would use less RAM if I use clumps, and have less forest objects.
I wasn't too happy with how it was looking anyway, so I'll have another go, but if I get stuck again I'll be sure to upload it.

Cheers,
Dean

[Neilg]

I've done a rug/full grass lawns with individual strands before and it's used up to 2gb max - forest should be saving you memory. for a single rug to use 14gb something is still wrong.

[notamondayfan]

OK, what's your email and I'll send it over, cheers

[chriserskine]

How are you rendering this?

if you are using light cache, try BF instead. light cache will use a lot of ram when scatter a lot of objects with something like forest pro.

[Svetlozar Draganov]

OK, what's your email and I'll send it over, cheers

Would it be possible to send the scene also to support@chaosgroup.com ?

[notamondayfan]

Hi Svetlozar,

I have sent an email with a link to the file for you to download.

Cheers,
Dean

[notamondayfan]

How are you rendering this?

if you are using light cache, try BF instead. light cache will use a lot of ram when scatter a lot of objects with something like forest pro.

I was using IM LC, just ran a test now and it perhaps is slightly faster, but it's definitly not running at 100% CPU power, more like 20% on both the local and node.

Cheers,
Dean

[notamondayfan]

OK I think it was down to the rug / forest pro. I've rebuilt it using different techniques (clumps).

I had gone over the recommended 500,000 number of items in the scatter, so this was where my problem was. I must say Forest Pro is amazing once you read the manual!!

Dean

[Svetlozar Draganov]

Thank you very much for your feedback.