file system caching

Why would you do that?  In general use, file caching gives significant benefit.

usually it is difficult to get the memory real usage because of the filesystem caching.

I do not see the benefits of fs caching in networker server

NW database resides on disk and cache might give you a hand there (depending on size of cache of course).  Hint: Disable fs cache and verify change in CPU load and speed of execution tasks (especially those with jobdb).

As I said, in general caching is recommended.  But of course there is a another side of the coin.  write cache for example may lead to potential corruption.  If your system is capable to handle the load without performance bottlenecks and you are after absolute security then disabling fs cache is good idea.  There is no right or wrong decision as everything comes with some sort of penalty.  Cache on storage arrays today takes care of pretty much everything and I/O on server (especially intel platform) should be enough to cope with higher loads.  That suggests there might be reason to switch it off.  But it entirely depends from case to case and requirements.  The only way to see impact is to test it.  My original though was you are dealing with some sort of performance issues and were testing wheter it helps or not... if this is not the case, then road which leads to disabling might not be that bad.  But you should really test it first to get an idea of impact (if any in your case).