sched/numa: Spread memory according to CPU and memory use
The pseudo-interleaving in NUMA placement has a fundamental problem: using hard usage thresholds to spread memory equally between nodes can prevent workloads from converging, or keep memory "trapped" on nodes where the workload is barely running any more. In order for workloads to properly converge, the memory migration should not be stopped when nodes reach parity, but instead be distributed according to how heavily memory is used from each node. This way memory migration and task migration reinforce each other, instead of one putting the brakes on the other. Remove the hard thresholds from the pseudo-interleaving code, and instead use a more gradual policy on memory placement. This also seems to improve convergence of workloads that do not run flat out, but sleep in between bursts of activity. We still want to slow down NUMA scanning and migration once a workload has settled on a few actively used nodes, so keep the 3/4 hysteresis in place. Keep track of whether a workload is actively running on multiple nodes, so task_numa_migrate does a full scan of the system for better task placement. In the case of running 3 SPECjbb2005 instances on a 4 node system, this code seems to result in fairer distribution of memory between nodes, with more memory bandwidth for each instance. Signed-off-by: NRik van Riel <riel@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: mgorman@suse.de Link: http://lkml.kernel.org/r/20160125170739.2fc9a641@annuminas.surriel.com [ Minor readability tweaks. ] Signed-off-by: NIngo Molnar <mingo@kernel.org>
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