linux-kernel - Re: [PATCH] sched, numa: Use {cpu, pid} to create task groups for shared faults

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Message-ID: <51F93105.8020503@hp.com>
Date:	Wed, 31 Jul 2013 11:45:09 -0400
From:	Don Morris <don.morris@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Mel Gorman <mgorman@...e.de>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched, numa: Use {cpu, pid} to create task groups for
 shared faults

On 07/31/2013 11:07 AM, Peter Zijlstra wrote:
> 
> New version that includes a final put for the numa_group struct and a
> few other modifications.
> 
> The new task_numa_free() completely blows though, far too expensive.
> Good ideas needed.
> 
> ---
> Subject: sched, numa: Use {cpu, pid} to create task groups for shared faults
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Tue Jul 30 10:40:20 CEST 2013
> 
> A very simple/straight forward shared fault task grouping
> implementation.
> 
> Concerns are that grouping on a single shared fault might be too
> aggressive -- this only works because Mel is excluding DSOs for faults,
> otherwise we'd have the world in a single group.
> 
> Future work could explore more complex means of picking groups. We
> could for example track one group for the entire scan (using something
> like PDM) and join it at the end of the scan if we deem it shared a
> sufficient amount of memory.
> 
> Another avenue to explore is that to do with tasks where private faults
> are predominant. Should we exclude them from the group or treat them as
> secondary, creating a graded group that tries hardest to collate shared
> tasks but also tries to move private tasks near when possible.
> 
> Also, the grouping information is completely unused, its up to future
> patches to do this.
> 
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> ---
>  include/linux/sched.h |    4 +
>  kernel/sched/core.c   |    4 +
>  kernel/sched/fair.c   |  177 +++++++++++++++++++++++++++++++++++++++++++++++---
>  kernel/sched/sched.h  |    5 -
>  4 files changed, 176 insertions(+), 14 deletions(-)

> +
> +static void task_numa_free(struct task_struct *p)
> +{
> +	kfree(p->numa_faults);
> +	if (p->numa_group) {
> +		struct numa_group *grp = p->numa_group;

See below.

> +		int i;
> +
> +		for (i = 0; i < 2*nr_node_ids; i++)
> +			atomic_long_sub(p->numa_faults[i], &grp->faults[i]);
> +
> +		spin_lock(&p->numa_lock);
> +		spin_lock(&group->lock);
> +		list_del(&p->numa_entry);
> +		spin_unlock(&group->lock);
> +		rcu_assign_pointer(p->numa_group, NULL);
> +		put_numa_group(grp);

So is the local variable group or grp here? Got to be one or the
other to compile...

Don

> +	}
> +}
> +
>  /*
>   * Got a PROT_NONE fault for a page on @node.
>   */

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