linux-kernel - Re: slab: start_cpu_timer/cache_reap CONFIG_HOTPLUG

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Message-ID: <Pine.LNX.4.64.0701291224340.32740@schroedinger.engr.sgi.com>
Date:	Mon, 29 Jan 2007 12:29:15 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Oleg Nesterov <oleg@...sign.ru>
cc:	Ingo Molnar <mingo@...e.hu>, Srivatsa Vaddagiri <vatsa@...ibm.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Gautham shenoy <ego@...ibm.com>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org
Subject: Re: slab: start_cpu_timer/cache_reap CONFIG_HOTPLUG_CPU problems

On Mon, 29 Jan 2007, Oleg Nesterov wrote:

> > But we could delay CPU_DOWN in the handler for the slab until we know that 
> > the cache_reaper is no longer running?
> 
> Hmm... I don't undestand this. We can delay CPU_DOWN if we cancel cache_reaper
> like you did in the previous patch. Did you mean this? If yes - then yes :)

Yes sure.

> Worse, we can have 2 handlers running in parallel on the same CPU. But this
> is fixed by your previous patch, I believe.

Good.

Here is the patch against 2.6.20-rc6-mm2. CPU_DOWN_PREPARE and
CPU_DOWN_FAILED somehow vanished in mm?





Shutdown cache_reaper when cpu goes down

Shutdown the cache_reaper in slab.c if the cpu is brought down
and set the cache_reap.func to NULL. Otherwise hotplug shuts
down the reaper for good.

Signed-off-by: Christoph Lameter <clameter@....com>

Index: linux-2.6.20-rc6-mm1/mm/slab.c
===================================================================
--- linux-2.6.20-rc6-mm1.orig/mm/slab.c	2007-01-29 14:18:37.000000000 -0600
+++ linux-2.6.20-rc6-mm1/mm/slab.c	2007-01-29 14:21:18.119155877 -0600
@@ -1271,6 +1271,17 @@ static int __cpuinit cpuup_callback(stru
 		start_cpu_timer(cpu);
 		break;
 #ifdef CONFIG_HOTPLUG_CPU
+  	case CPU_DOWN_PREPARE:
+		/* Shutdown cache reaper */
+		cancel_rearming_delayed_work(&per_cpu(reap_work, cpu));
+		per_cpu(reap_work, cpu).work.func = NULL;
+
+  		mutex_lock(&cache_chain_mutex);
+  		break;
+  	case CPU_DOWN_FAILED:
+  		mutex_unlock(&cache_chain_mutex);
+		start_cpu_timer(cpu);
+  		break;
 	case CPU_DEAD:
 		/*
 		 * Even if all the cpus of a node are down, we don't free the
-
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