Linux NUMA Patches Aim To Reduce Overhead, Avoid Unnecessary Migrations

A set of patches that continue to be worked on for the Linux kernek is reconciling NUMA balancing decisions with the load balancer. Ultimately this series is about reducing unnecessary task and page migrations and other NUMA balancing overhead.

The main focus with the patch series is addressing inconsistencies between the kernel's NUMA balancing code and the load balancer. "The NUMA balancer makes placement decisions on tasks that partially take the load balancer into account and vice versa but there are inconsistencies. This can result in placement decisions that override each other leading to unnecessary migrations -- both task placement and page placement. This series reconciles many of the decisions -- partially Vincent's work with some fixes and optimisations on top to merge our two series."

The patch series by Mel Gorman and Vincent Guittot also provide other optimizations and improvements, including a case where the NUMA balancer could be fighting with itself.

For some workloads this patch series does help the performance but it doesn't provide across the board benefits but at least helps with unnecessary migrations and lowering overhead. The patch series is up to its fourth round of review and hopefully will soon be mainlined in a forthcoming cycle for helping to clean up the Linux kernel's NUMA code.