[Ksummit-discuss] No more module removal -- Unconference track

[Masami Hiramatsu]

(2014/08/19 23:55), Guenter Roeck wrote:
> On Tue, Aug 19, 2014 at 10:48:39AM -0400, Theodore Ts'o wrote:
>> This has been scheduled at 2pm at the request of Rusty.  (Reminder: if
>> you're going to propose a topic, please send e-mail to start a thread
>> on ksummit-discuss).
>>
> Do we have a context ? I am using insert/remove module a lot during testing,
> and would hate to see it go. It also permits module updates without having to
> reboot the kernel. There must be lots of other reasons to support module
> removal. So I would really dislike if it was no longer available, and I don't
> really see the point.

I have to explain why, since I asked Rusty to improving removing.

What I found is that the module unloading involving 2 stop_machine()s
for each module removing. It must not be needed. However, since the
module's ref-counter is over-optimized for BIG SMP machine, we can't
remove it without replacing it. But it means some performance
regression can happen on such big-scale SMP machines (not the laptop nor
normal smp machine).
So I asked him to introduce something like lock-up option which locks
up the given module, and the kernel skips ref-counting on that module.

Anyway, I sent the series right now :)

https://lkml.org/lkml/2014/8/25/142

Please check it if it is good for your use-cases.

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt at hitachi.com