Speculative NUMA fault support offered to improve Linux memory performance on several levels


This year, there has been a lot of work on the Linux kernel to improve the handling of memory servers on several levels, namely those with traditional system RAM augmented by Intel Optane DC persistent memory. Work has been done to demote pages when recovering to slower persistent memory, improving NUMA balancing around these systems to optimize memory placement, transparent page placement, and related work around Linux servers with hierarchical memory.

The latest work comes from Alibaba and they offer speculative NUMA fault support for multi-tiered memory systems. The fixes offered for speculative NUMA fault support will manage the promotion of slow / hot memory to fast memory to improve system performance.

This RFC patch set adds speculative support for Numa errors for certain scenarios, such as multi-tiered memory system. On the multilevel memory system, it will rely on digital balancing to promote slow and hot memory to fast memory to improve performance. So, we can promote multiple sequential pages on slow memory in advance based on data locality for certain workloads to improve performance.

So now how many pages should be promoted in fast memory the best? Now, this RFC patch set only implements a basic and simple mechanism to speculate on the numa error window for each VMA. It will introduce a new atomic member for each VMA to record the Numa failure window information, which is used to determine if this is a sequential stream to extend or reduce the Numa failure window.

The patch series is under a “request for comment” flag and is equivalent to processing just over 200 lines of memory management code at this point. The results are promising with this basic / simple mechanism already showing about a 6% performance improvement for MySQL on a tiered memory server.

It’s great to see these Linux multi-level memory performance optimizations continue ahead of next-gen servers where we expect more persistent memory usage.

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