Re: [PATCH v5 5/5] lib/percpu-list: Add a config parameter for disabling per-cpu list

[Waiman Long <waiman.long@hpe.com>]

On 03/02/2016 03:41 AM, Ingo Molnar wrote:
> * Waiman Long<Waiman.Long@hpe.com>  wrote:
>
>> As there is concern that the larger pcpu_list_node structure and the
>> per-cpu overhead may be a waste of resource on small system. This patch
>> adds a config parameter CONFIG_PERCPU_LIST to disable the per-cpu list
>> if the kernel builder chooses to do so. With per-cpu list disabled,
>> all the different groups of per-cpu lists will be degenerated into
>> global lists for all the CPUs.
>>
>> The current default is to enable per-cpu list. A kernel builder needs
>> to explicitly turn it off.
>>
>> Signed-off-by: Waiman Long<Waiman.Long@hpe.com>
>> ---
>>   fs/inode.c                  |    2 +-
>>   include/linux/percpu-list.h |   93 ++++++++++++++++++++++++++++++++++++++++++-
>>   lib/Kconfig                 |   14 ++++++
>>   lib/percpu-list.c           |   24 +++++++++++-
>>   4 files changed, 130 insertions(+), 3 deletions(-)
> I think this kind of #ifdef complexity and the doubling of our Kconfig and testing
> space is counterproductive, and I think the per CPU locking is a win on as small
> as dual core CPUs, and on UP CPUs the per CPU list becomes a single global list
> automatically.
>
> I'm not against visible memory savings for overly clever scalability features, but
> this does not appear to be such a case, so:
>
> NAKed-by: Ingo Molnar<mingo@kernel.org>
>
> Thanks,
>
> 	Ingo

The last patch was there to answer a feedback from Jan. I am fine if 
that is not merged as I prefer to have the per-cpu list capability as 
the default anyway.

Cheers,
Longman