Efficient use of POSIX shared memory in a c++ program

Question

I'm using shared memory based on POSIX API on a linux machine to communicate between multiple MPI process. I have a working solution but I want to know how to make efficient use of the shared memory space for large data.

I have a machine with 64GB shared memory limit and it might happen that I have to write data > 64GB into this space, but these are smaller chunks of 1-2GB.

What I want to know is this:

• How can I really delete the memory occupied by my 1-2GB chunk as soon as it's purpose is served and I don't want that data anymore?

I'm using shm_unlink() but it doesn't seem to clear space in /dev/shm/

Please help!

Answer 1

From the sum_unlink description in http://pubs.opengroup.org/onlinepubs/009695399/functions/shm_unlink.html it seems that the memory removal may be actually postponed, read below:

If one or more references to the shared memory object exist when the object is unlinked, the name shall be removed before shm_unlink() returns, but the removal of the memory object contents shall be postponed until all open and map references to the shared memory object have been removed.

I hope this help.