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

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Date:	Mon, 29 Jan 2007 22:29:57 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Christoph Lameter <clameter@....com>
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 01/29, Christoph Lameter wrote:
>
> On Mon, 29 Jan 2007, Oleg Nesterov wrote:
> 
> > >                                      The slab would need a notification 
> > > that the workqueue for a processor was shutdown in order to set work.func 
> > > = NULL.
> > 
> > The slab has a notification: CPU_XXX events. It should cancel a pending per
> > cpu "reap_work timer".
> 
> Ahh. Okay then the following patch would fix it?
> 
> 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/mm/slab.c
> ===================================================================
> --- linux-2.6.20-rc6.orig/mm/slab.c	2007-01-24 20:19:28.000000000 -0600
> +++ linux-2.6.20-rc6/mm/slab.c	2007-01-29 13:08:05.773928988 -0600
> @@ -1269,6 +1269,10 @@ static int __cpuinit cpuup_callback(stru
>  		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:

Then CPU_DOWN_FAILED should do start_cpu_timer(cpu).

Oleg.

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