linux-kernel - Re: [PATCH 26/31] sched, numa, mm: Add fault driven placement and migration policy

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Date:	Tue, 30 Oct 2012 15:23:22 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 26/31] sched, numa, mm: Add fault driven placement and
 migration policy

On 10/25/2012 08:16 AM, Peter Zijlstra wrote:
> +/*
> + * Drive the periodic memory faults..
> + */
> +void task_tick_numa(struct rq *rq, struct task_struct *curr)
> +{
> +	struct callback_head *work = &curr->numa_work;
> +	u64 period, now;
> +
> +	/*
> +	 * We don't care about NUMA placement if we don't have memory.
> +	 */
> +	if (!curr->mm || (curr->flags & PF_EXITING) || work->next != work)
> +		return;

We should probably skip the whole unmap-and-refault
business if we are running on a system that is not
NUMA.  Ie. a system with just one node...

> +	/*
> +	 * Using runtime rather than walltime has the dual advantage that
> +	 * we (mostly) drive the selection from busy threads and that the
> +	 * task needs to have done some actual work before we bother with
> +	 * NUMA placement.
> +	 */
> +	now = curr->se.sum_exec_runtime;
> +	period = (u64)curr->numa_scan_period * NSEC_PER_MSEC;
> +


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