This is a feature to be desired because the current data pump tool cannot do it. Have you all noticed that while running expdp to create a big dumpfile, the OS free memory quickly goes down and you start to see kernel thread [kswapd] in `top' output, unless you had tons of free memory at the beginning? This is on Linux and file system is xfs. Unlike Solaris, Linux has no way to enable file system-wide direct I/O. It has to be enabled by the program, i.e. set the O_DIRECT flag to the open(2) call (see `man 2 open'). The expdp developer can do this easily. But this is not possible with the current data pump tools. (Oracle 19c, if version matters.)
[Update]
I thought I found the solution by using the nocache program (https://github.com/Feh/nocache). So I installed it and prepended nocache to the data pump command, i.e. `nocache expdp ...'. It did not work. The system free memory still drastically dropped as soon as expdp finished preparations and started to actually dump data.
Prepending `nocache' to expdp is equivalent to
export LD_PRELOAD=<dir where I installed nocache>/nocache-master/nocache.so
followed by expdp. But the data pump master and worker processes ora_dm* and ora_dw* do not inherit this environment variable from expdp.
It would be a nice enhancement if data pump could have a nocache-like option built in.
[10/11/2022 Update] The enhancement request was rejected in SR 3-29996935781 because, according to the analyst, "Caching behavior on Linux is OS-specific. It belongs at the file layer on which Data Pump relies. This request makes assumptions and suggests a solution when the root cause of the problem is unclear. It has not been reported by any other customer and Data Pump is used on Linux all the time." I wish somebody else could petition to Oracle for this simple change. The statement "the root cause of the problem is unclear" makes me speechless. I wish the Oracle analyst had at least a few days of systems programming experience, and he/she would know I already presented the root cause and the simple solution.