linux-kernel - Re: [PATCH] kthread: ensure locality of task

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Date:	Wed, 29 Jan 2014 00:13:47 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Anton Blanchard <anton@...ba.org>,
	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Jan Kara <jack@...e.cz>, Thomas Gleixner <tglx@...utronix.de>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-mm@...ck.org, Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Ben Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] kthread: ensure locality of task_struct allocations

On Tue, 28 Jan 2014, Nishanth Aravamudan wrote:

> In the presence of memoryless nodes, numa_node_id()/cpu_to_node() will
> return the current CPU's NUMA node, but that may not be where we expect
> to allocate from memory from. Instead, we should use
> numa_mem_id()/cpu_to_mem(). On one ppc64 system with a memoryless Node
> 0, this ends up saving nearly 500M of slab due to less fragmentation.
> 
> Signed-off-by: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>

Acked-by: David Rientjes <rientjes@...gle.com>

> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index b5ae3ee..8573e4e 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -217,7 +217,7 @@ int tsk_fork_get_node(struct task_struct *tsk)
>  	if (tsk == kthreadd_task)
>  		return tsk->pref_node_fork;
>  #endif
> -	return numa_node_id();
> +	return numa_mem_id();

I'm wondering why return NUMA_NO_NODE wouldn't have the same effect and 
prefer the local node?
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