Persistent memory garbage collection

A persistent memory garbage collection apparatus comprising:

• a processor;
• and
• a memory storing machine readable instructions that when executed by the processor cause the processor to:
• determine whether termination of a program is based on a specified termination of the program during execution of the program or an unspecified termination of the program during the execution of the program;
• identify unallocated memory from a persistent memory in a free-list data structure that includes an object free-list and a page free-list, wherein:
• the free-list data structure is maintained in persistent metadata of the persistent memory to identify portions of the persistent memory that have not been allocated,
• the object free-list is a singly-linked list of the free objects that includes a link to a next object in the singly-linked list, and
• the page free-list comprises contiguous free space that is page-sized or larger;
• in response to a determination that the termination of the program is based on the specified termination of the program during the execution of the program, utilize the persistent metadata stored in the persistent memory to restart the program, wherein the persistent metadata comprises a first root address associated with a persistent heap of data;
• determine a reclaiming process to associate a data object with garbage that is independent from the execution of the program;
• and
• in response to a determination that the termination of the program is based on the unspecified termination of the program during the execution of the program:
• determine the data object within the persistent heap of data is not reachable by a second root address associated with the data object;
• initiate the reclaiming process to associate the data object with garbage and to restart the program, wherein the reclaiming process comprises:
• releasing memory objects in the free-list data structure and a reclaim list,
• rebuilding the reclaim list to include a list of memory pages where memory objects in use have been marked, but free memory objects have not yet been reclaimed, and
• refilling the object-free list of the free-list data structure by splitting the contiguous free space from the page-free list of the free-list data structure;
• and
• responsive to completing the reclaiming process, close the persistent heap of data.

A non-transitory computer readable medium having stored thereon machine readable instructions to provide persistent memory garbage collection, the machine readable instructions, when executed, cause a processor to:

• identify unallocated memory from a persistent memory in a free-list data structure included in persistent metadata stored in the persistent memory, wherein:
• the free-list data structure includes an object free-list and a page free-list,
• the free-list data structure is maintained to identify portions of the persistent memory that have not been allocated,
• the object free-list is a singly-linked list of the free objects that includes a link to a next object in the singly-linked list, and
• the page free-list comprises contiguous free space that is page-sized or larger;
• identify modifications related to allocation of the persistent memory in a consistency log included in the persistent metadata;
• determine whether termination of a program is based on a specified termination of the program during execution of the program or an unspecified termination of the program during the execution of the program;
• in response to a determination that the termination of the program is based on the specified termination of the program during the execution of the program, utilize the persistent metadata to restart the program, wherein the persistent metadata comprises a first root address associated with a persistent heap of data;
• and
• in response to a determination that the termination of the program is based on the unspecified termination of the program during the execution of the program:
• determine a data object within the persistent heap of data is not reachable by a second root address associated with the data object;
• initiate a reclaiming process to associate the data object with garbage and to restart the program, wherein the reclaiming process comprises:
• releasing memory objects in the free-list data structure and a reclaim list,
• rebuilding the reclaim list to include a list of memory pages where memory objects in use have been marked, but free memory objects have not yet been reclaimed, and
• refilling the object-free list of the free-list data structure by splitting the contiguous free space from the page-free list of the free-list data structure;
• and
• responsive to completing the reclaiming process, close the persistent heap of data.