| Date | Tue, 5 Jun 2018 10:58:43 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 18/19] sched/numa: Reset scan rate whenever task moves across nodes |
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On Mon, Jun 04, 2018 at 03:30:27PM +0530, Srikar Dronamraju wrote: > Currently task scan rate is reset when numa balancer migrates the task > to a different node. If numa balancer initiates a swap, reset is only > applicable to the task that initiates the swap. Similarly no scan rate > reset is done if the task is migrated across nodes by traditional load > balancer. > > Instead move the scan reset to the migrate_task_rq. This ensures the > task moved out of its preferred node, either gets back to its preferred > node quickly or finds a new preferred node. Doing so, would be fair to > all tasks migrating across nodes. >
By and large you need to be very careful resetting the scan rate without a lot of justification and I don't think this is enough. With scan rate resets, there is a significant risk that system CPU overhead is increased to do the page table updates and handle the resulting minor faults. There are cases where tasks can get pulled cross-node very frequently and we do not want NUMA balancing scanning agressively when that happens.
-- Mel Gorman SUSE Labs
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