[Devel] Re: [PATCH 2/5] Generic notifiers for SLUB events

[Balbir Singh]

Pavel Emelyanov wrote:
> If the user wants more than one listener for SLUB event,
> it can register them all as notifier_block-s so all of
> them will be notified.
> 
> This costs us about 10% of performance loss, in comparison
> with static linking.
> 
> The selected method of notification is srcu notifier blocks.
> This is selected because the "call" path, i.e. when the 
> notification is done, is lockless and at the same time the
> handlers can sleep. Neither regular nor atomic notifiers
> provide such facilities.
> 
> Signed-off-by: Pavel Emelyanov <xemul at openvz.org>
> 
> ---
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 684ccfb..e9acc29 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -593,6 +599,16 @@ config SLUB_DEBUG
>  	  SLUB sysfs support. /sys/slab will not exist and there will be
>  	  no support for cache validation etc.
> 
> +config SLUB_NOTIFY
> +	default y

Should the default be on? Shouldn't it depend on KMEM?

> +	bool "Enable SLUB events generic notification"
> +	depends on SLUB
> +	help
> +	  When Y, this option enables generic notifications of some major
> +	  slub events. However, if you do know that there will be the
> +	  only listener for them, you may say N here, so that callbacks
> +	  will be called directly.
> +
> -
> -
> +#ifdef CONFIG_SLUB_NOTIFY
> +	srcu_init_notifier_head(&slub_nb);

Can we get rid of the #ifdef CONFIG_SLUB_NOTIFY?

> +#endif
>  	printk(KERN_INFO "SLUB: Genslabs=%d, HWalign=%d, Order=%d-%d, MinObjects=%d,"
>  		" CPUs=%d, Nodes=%d\n",
>  		caches, cache_line_size(),
> 


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL