linux-kernel - Re: [PATCH v3 01/17] hashtable: introduce a small and naive hashtable

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Message-ID: <20120904163220.GA31698@Krystal>
Date:	Tue, 4 Sep 2012 12:32:20 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Sasha Levin <levinsasha928@...il.com>, Tejun Heo <tj@...nel.org>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	paul.gortmaker@...driver.com, davem@...emloft.net, mingo@...e.hu,
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Subject: Re: [PATCH v3 01/17] hashtable: introduce a small and naive
	hashtable

* Steven Rostedt (rostedt@...dmis.org) wrote:
> On Tue, 2012-08-28 at 19:00 -0400, Mathieu Desnoyers wrote:
> 
> > Looking again at:
> > 
> > +#define hash_for_each_size(name, bits, bkt, node, obj, member)                 \
> > +       for (bkt = 0; bkt < HASH_SIZE(bits); bkt++)                             \
> > +               hlist_for_each_entry(obj, node, &name[bkt], member)
> > 
> > you will notice that a "break" or "continue" in the inner loop will not
> > affect the outer loop, which is certainly not what the programmer would
> > expect!
> > 
> > I advise strongly against creating such error-prone construct.
> > 
> 
> A few existing loop macros do this. But they require a do { } while ()
> approach, and all have a comment.
> 
> It's used by do_each_thread() in sched.h 

Yes. It's worth noting that it is a do_each_thread() /
while_each_thread() pair.


> and ftrace does this as well.
> Look at kernel/trace/ftrace.c at do_for_each_ftrace_rec().

Same here.

> 
> Yes it breaks 'break' but it does not break 'continue' as it would just
> go to the next item that would have been found (like a normal for
> would).

Good point.

So would changing hash_for_each_size() to a

do_each_hash_size()/while_each_hash_size() make it clearer that this
contains a double-loop ? (along with an appropriate comment about
break).

Thanks,

Mathieu

> 
> -- Steve
> 
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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