Resilient system uses only non-volatile memory

Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed hardware and software technology that is said to ensure both data and execution persistence. The Lightweight Persistence Centric System (LightPC) makes the systems resilient against power failures by utilising only non-volatile memory as the main memory.

“We mounted non-volatile memory on a system board prototype and created an operating system to verify the effectiveness of LightPC,” said research leader Professor Myoungsoo Jung. The team said the LightPC validated its execution while powering up and down in the middle of execution, showing up to eight times more memory, 4.3 times faster application execution and 73% lower power consumption compared to traditional systems.

In general, power failures on legacy systems can lead to the loss of data stored in the DRAM-based main memory. Unlike volatile memory such as DRAM, non-volatile memory can retain its data without power. Although non-volatile memory has the characteristics of lower power consumption and larger capacity than DRAM, non-volatile memory is typically used for the task of secondary storage due to its lower write performance. For this reason, non-volatile memory is often used with DRAM. However, modern systems employing non-volatile memory-based main memory experience unexpected performance degradation due to the complicated memory microarchitecture.

To enable both data and execution persistent in legacy systems, it is necessary to transfer the data from the volatile memory to the non-volatile memory. Checkpointing is one possible solution: it periodically transfers the data in preparation for a sudden power failure. While this technology is essential for ensuring high mobility and reliability for users, checkpointing also has fatal drawbacks. It takes additional time and power to move data and requires a data recovery process as well as restarting the system.

In order to address these issues, the research team developed a processor and memory controller to raise the performance of non-volatile memory-only memory. LightPC matches the performance of DRAM by minimising the internal volatile memory components from non-volatile memory, exposing the non-volatile memory (PRAM) media to the host, and increasing parallelism to service on-the-fly requests as soon as possible.

The team also presented operating system technology that quickly makes execution states of running processes persistent without the need for a checkpointing process. The operating system prevents all modifications to execution states and data by keeping all program executions idle before transferring data in order to support consistency within a period much shorter than the standard power hold-up time of about 16 minutes. For consistency, when the power is recovered, the computer almost immediately revives itself and re-executes all the offline processes immediately without the need for a boot process.

Jung said that LightPC can be utilised in a variety of fields such as data centres and high-performance computing to provide large-capacity memory, high performance, low power consumption and service reliability. The team will present their work at the International Symposium on Computer Architecture (ISCA) 2022 in New York in June.

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