Optimization Settings for displacement

[rikou]

Hi
I've got problems with displacement. I have stone walls with a mix of 2 bitmaps and a noise to blend them inf diffuse. I use this mix to displace my wall
(first, I'm not sure if it's such a good idea ?). I precal' my IR and my LC without displacement . So my goal now is to render a 4000px WITH my displacement.
My setting is default setting except edge lenght to 3pix and edge tresh to 0.005.
(I can't accept to go beyond 4pix without lose too much details)
All my walls are subdivided.

Anyway, "unloading geometry" appears, displacement make my render time completely skyrocket to the point of being unusable.
Dynamic memory limit push to 6000Mb (8Go RAM pc's).
I' looking for advices
What's the best way to avoid that problem ?
How can I optimize this scene ?
thanks a lot for your help

[rikou]

Something is strange, I tested some setting and my last test was with default setting for VRayDisplacementMod.
Edge Lenght : 4pix
View-dependant : on
Max subdiv : 256
and edge thresh : 0,005

It was ok , the 1st half of my image was calculated without any problems , but now buckets stopped, are stuck, nothing new since the last 2 hours...
I can understand why.... The first part took something like 1 hour without problem and suddely... all is stuck

[joconnell]

Have you hit part of the scene that has bad geometry? It might be worth trying to render in sections with some overlap so you can chase it down to part of your image that has issues.

[rikou]

You're right, I'll try and let you know
It seems to be very localized...

Thx

[rikou]

A newbie question :
I know about all the rest but does "Global subdiv multiplier" affect subdivs of VRayDisplacementMod ?