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

[Waiman Long]

On 03/02/2016 03:41 AM, Ingo Molnar wrote:
> * Waiman Long<Waiman.Long@xxxxxxx>  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@xxxxxxx>
> > ---
> >   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@xxxxxxxxxx>
>
> 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