Re: [PATCH 17/18] sched: Retry migration of tasks to CPU on apreferred node

From: Mel Gorman
Date: Thu Aug 01 2013 - 11:46:14 EST

On Thu, Aug 01, 2013 at 10:43:27AM +0530, Srikar Dronamraju wrote:
> * Mel Gorman <mgorman@xxxxxxx> [2013-07-15 16:20:19]:
> > When a preferred node is selected for a tasks there is an attempt to migrate
> > the task to a CPU there. This may fail in which case the task will only
> > migrate if the active load balancer takes action. This may never happen if
> Apart from load imbalance or heavily loaded cpus on the preferred node,
> what could be the other reasons for migration failure with
> migrate_task_to()?

These were the reasons I expected that migration might fail.

> I see it almost similar to active load balance except
> for pushing instead of pulling tasks.
> If load imbalance is the only reason, do we need to retry? If the task
> is really so attached to memory on that node, shouldn't we getting
> task_numa_placement hit before the next 5 seconds?

Depends on the PTE scanning rate.

Mel Gorman
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