Re: slab: start_cpu_timer/cache_reap CONFIG_HOTPLUG_CPU problems

[Oleg Nesterov <oleg@tv-sign.ru>]

On 01/29, Christoph Lameter wrote:
>
> Here is the patch against 2.6.20-rc6-mm2. CPU_DOWN_PREPARE and
> CPU_DOWN_FAILED somehow vanished in mm?

No, no, there are still in place, so I believe your patch is good.

Now we have 2 additional events, CPU_LOCK_ACQUIRE/CPU_LOCK_RELEASE,
so cpuup_callback() can use them to lock/unlock cache_chain_mutex,
but this is not related.

> 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@sgi.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