linux-kernel - Re: [PATCH v2 3/4] sched:Fix task_numa_migrate to always update preferred node

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <55805A7B.3070600@redhat.com>
Date:	Tue, 16 Jun 2015 13:18:51 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH v2 3/4] sched:Fix task_numa_migrate to always update preferred
 node

On 06/16/2015 07:56 AM, Srikar Dronamraju wrote:

> @@ -1519,16 +1519,9 @@ static int task_numa_migrate(struct task_struct *p)
>  	 * and is migrating into one of the workload's active nodes, remember
>  	 * this node as the task's preferred numa node, so the workload can
>  	 * settle down.
> -	 * A task that migrated to a second choice node will be better off
> -	 * trying for a better one later. Do not set the preferred node here.
>  	 */
>  	if (p->numa_group) {
> -		if (env.best_cpu == -1)
> -			nid = env.src_nid;
> -		else
> -			nid = env.dst_nid;
> -
> -		if (node_isset(nid, p->numa_group->active_nodes))
> +		if (env.dst_nid != p->numa_preferred_nid)
>  			sched_setnuma(p, env.dst_nid);
>  	}

Looking at the original code again, it looks like my code
has a potential bug (or at least downside), too.

We set p->numa_group->active_nodes depending on which nodes
a group triggers many NUMA faults happen from (the CPUs the
tasks in the group were running on when they had NUMA faults).

This means if a workload is not yet converged, the active_nodes
mask may be much larger than desired, and we can end up setting
p->numa_preferred_nid to a node that is currently in the active_nodes
mask, but really shouldn't be...

I have no ideas on how to improve that situation, though :)

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/