NBR: Neutralization Based Reclamation

TL;DR

The paper introduces NBR, a new memory reclamation algorithm that is faster than existing methods and guarantees bounded unreclaimed memory, using a simple, non-blocking approach suitable for various data structures.

Contribution

NBR is a novel neutralization-based reclamation algorithm that outperforms state-of-the-art algorithms in speed while ensuring bounded unreclaimed memory and ease of use.

Findings

NBR is up to 38% faster than DEBRA in binary search trees.

NBR outperforms HP by up to 17% in binary search trees.

NBR is 15% to 243% faster than DEBRA and HP in linked list benchmarks.

Abstract

Safe memory reclamation (SMR) algorithms suffer from a trade-off between bounding unreclaimed memory and the speed of reclamation. Hazard pointer (HP) based algorithms bound unreclaimed memory at all times, but tend to be slower than other approaches. Epoch based reclamation (EBR) algorithms are faster, but do not bound memory reclamation. Other algorithms follow hybrid approaches, requiring special compiler or hardware support, changes to record layouts, and/or extensive code changes. Not all SMR algorithms can be used to reclaim memory for all data structures. We propose a new neutralization based reclamation (NBR) algorithm that is faster than the best known EBR algorithms and achieves bounded unreclaimed memory. It is non-blocking when used with a non-blocking operating system (OS) kernel, and only requires atomic read, write and CAS. NBR is straightforward to use with many different data structures, and in most cases, require similar reasoning and programmer effort to two-phased locking. NBR is implemented using OS signals and a lightweight handshaking mechanism between participating threads to determine when it is safe to reclaim a record. Experiments on a lock-based binary search tree and a lazy linked list show that NBR significantly outperforms many state of the art reclamation algorithms. In the tree NBR is faster than next best algorithm, DEBRA by upto 38% and HP by upto 17%. And, in the list NBR is 15% and 243% faster than DEBRA and HP, respectively.