Freeing Persistent Memory

Just like any process, a restartable process can free persistent memory blocks using pmmFree() or pmmFreeAll(). This is described in "Freeing a Persistent Memory Block".

Restartable processes which allocate memory with pmmAllocate() can also use a basic automatic deallocation mechanism provided by the Hot Restart Controller. This saves the process from having to free its persistent memory explicitly. Instead, the persistent memory will remain allocated for the lifespan of the process's group, and then be freed automatically by the Hot Restart Controller when the last member of the process's restart group terminates cleanly. The disadvantage of this system is that the lifespan of the restart group may extend well beyond the point at which the memory block is no longer required. In this situation, the memory block will take up space in persistent memory unnecessarily.

To mark a persistent memory block for automatic de-allocation by the Hot Restart Controller, pass the macros HR_GROUP_KEY and HR_GROUP_KEYSIZE as the delKey and delKeySize arguments respectively in the call to pmmAllocate(). These macros tie the lifespan of the persistent memory block to the lifespan of the calling process's restart group.

A block marked for automatic de-allocation by the Hot Restart Controller can still be freed explicitly by calling pmmFree() with the block's PmmName. However, attempting to call pmmFreeAll() by passing the HR_GROUP_KEY and HR_GROUP_KEYSIZE macros will result in an error because this is not permitted.