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

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Date:	Tue, 28 Jan 2014 10:38:08 -0800
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	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>, David Rientjes <rientjes@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Ben Herrenschmidt <benh@...nel.crashing.org>
Subject: [PATCH] kthread: ensure locality of task_struct allocations

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>

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();
 }
 
 static void create_kthread(struct kthread_create_info *create)
@@ -369,7 +369,7 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
 {
 	struct task_struct *p;
 
-	p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
+	p = kthread_create_on_node(threadfn, data, cpu_to_mem(cpu), namefmt,
 				   cpu);
 	if (IS_ERR(p))
 		return p;

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