linux-kernel - Re: [PATCH] percpu: explain quick paths in pcpu_[de]populate

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Date:	Tue, 01 Dec 2009 14:09:50 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Cong Wang <amwang@...hat.com>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] percpu: explain quick paths in pcpu_[de]populate_chunk()

On 12/01/2009 02:00 PM, Tejun Heo wrote:
> I thought about that but didn't want to open code the special and
> fairly complex loop construct used there.  To me, it seemed using the
> same loop construct would be much less error-prone than open coding
> the loop mostly because those two special cases are the only place
> where that is necessary.  Maybe we can add pcpu_first_[un]pop_region()
> macros and use them there but is the first iteration check that bad
> even with sufficient explanations?

So, something like the following.

#define pcpu_first_unpop_region(chunk, rs, re, start, end)	do {	\
	(rs) = (start);							\
	pcpu_next_unpop((chunk), &(rs), &(re), (end));			\
} while (0)

#define pcpu_for_each_unpop_region(chunk, rs, re, start, end)		\
	for (pcpu_first_unpop_region(chunk, rs, re, start, end);	\
	     (rs) < (re);						\
	     (rs) = (re) + 1, pcpu_next_unpop((chunk), &(rs), &(re), (end)))

#define pcpu_first_pop_region(chunk, rs, re, start, end)	do {	\
	(rs) = (start);							\
	pcpu_next_pop((chunk), &(rs), &(re), (end));			\
} while (0)

#define pcpu_for_each_pop_region(chunk, rs, re, start, end)		\
	for (pcpu_first_pop_region(chunk, rs, re, start, end);		\
	     (rs) < (re);						\
	     (rs) = (re) + 1, pcpu_next_pop((chunk), &(rs), &(re), (end)))

It might be better to make these proper functions which take pointers
but that makes the only two interfaces for region iterators disagree
about how they take parameters.

So, I don't know.  The first iteration only loop looks a bit unusual
for sure but it isn't something conceptually convoluted.

Thanks.

-- 
tejun
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