linux-kernel - Re: [GIT PULL] percpu fixes for 2.6.32-rc6

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Date:	Thu, 12 Nov 2009 12:07:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yhlu.kernel@...il.com>
Subject: Re: [GIT PULL] percpu fixes for 2.6.32-rc6

* Tejun Heo <tj@...nel.org> wrote:

> >         if (reserved && pcpu_reserved_chunk) {
> > 
> > into a helper inline function, something like __pcpu_alloc_reserved().
> > 
> > It's a rare special case anyway. It could be changed to return with the 
> > pcpu_lock always taken, so the above branch would look like this:
> > 
> > 	if (unlikely(reserved)) {
> > 		off = __pcpu_alloc_reserved(&chunk, size, align, &err);
> > 		if (off < 0)
> > 			goto fail_unlock;
> > 		goto area_found;
> > 	}
> > 
> > Which is a cleaner flow IMO, and which simplifes pcpu_alloc().
> 
> Hmmm... The thing is that the nesting isn't that deep there [...]

Well, the pcpu_alloc() function is 115 lines which is a bit long. It 
does 2-3 things while a function should try to do one thing.

Putting the reserved allocation into a separate function also makes the 
'main' path of logic more visible and obstructed less by rare details.

The indentation i pinpointed is 4 levels deep:

                                err = "failed to extend area map of "
                                        "reserved chunk";

which is a bit too much IMO - the code starts in the middle of the 
screen, there's barely any space to do anything meaningful.

But there's other line wrap artifacts as well further down:

                                if (pcpu_extend_area_map(chunk,
                                                         new_alloc) < 0) {

But ... there's no hard rules here and i've seen functions where 4 
levels of indentation were just ok. Anyway, i just gave you my opinion, 
and i'm definitely more on the nitpicky side of the code quality 
equilibrium, YMMV.

	Ingo
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