How high do You usually set memory limit ?

On CL6 -- you should really use just physical memory and disable vitual memory at all (by setting it to 0). As soon as we push the new CL5 kernel with physical memory support, we will make it default.

 

whats the dif between physical and virtual and why disable virtual?

 

Physical memory corresponds to RES column in top. Virtual memory -- corresponds to VIRT column.
Per top man page:
VIRT -- Virtual Image (kb)
The total amount of virtual memory used by the task. It
includes all code, data and shared libraries plus pages that
have been swapped out and pages that have been mapped but not
used.

RES -- Resident size (kb)
The non-swapped physical memory a task has used.

I don't know how to explain what virtual memory is in non-technical terms. Here is the pretty good technical explanation: Solaris Troubleshooting and Performance Tuning.

Physical memory on the other hand is the most reasonable way to account for actual memory used.

 

Limit memory via LVE as needed. But also ensure you set the PHP memory limit as required to a decent level.