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

[Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

Balbir Singh wrote:
> 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-GEFAQzZX7r8dnm+yROfE0A@public.gmane.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?

Well... I think that is should be N by default and has
noting to do with the KMEM :) Thanks for noticing.

>> +	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?

I don't think this is really useful in the __init code :)

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