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

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Message-ID: <5048AAF6.5090101@gmail.com>
Date:	Thu, 06 Sep 2012 15:53:58 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC:	Pedro Alves <palves@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>, torvalds@...ux-foundation.org,
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	linux-mm@...ck.org, paul.gortmaker@...driver.com,
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Subject: Re: [PATCH v3 01/17] hashtable: introduce a small and naive hashtable

On 09/04/2012 07:01 PM, Mathieu Desnoyers wrote:
>> #define do_for_each_ftrace_rec(pg, rec)                                          \
>> >         for (pg = ftrace_pages_start, rec = &pg->records[pg->index];             \
>> >              pg && rec == &pg->records[pg->index];                               \
>> >              pg = pg->next)                                                      \
>> >           for (rec = pg->records; rec < &pg->records[pg->index]; rec++)
> Maybe in some cases there might be ways to combine the two loops into
> one ? I'm not seeing exactly how to do it for this one, but it should
> not be impossible. If the inner loop condition can be moved to the outer
> loop, and if we use (blah ? loop1_conf : loop2_cond) to test for
> different conditions depending on the context, and do the same for the
> 3rd argument of the for() loop. The details elude me for now though, so
> maybe it's complete non-sense ;)
> 
> It might not be that useful for do_for_each_ftrace_rec, but if we can do
> it for the hash table iterator, it might be worth it.

So I think that for the hash iterator it might actually be simpler.

My solution to making 'break' work in the iterator is:

	for (bkt = 0, node = NULL; bkt < HASH_SIZE(name) && node == NULL; bkt++)
		hlist_for_each_entry(obj, node, &name[bkt], member)

We initialize our node loop cursor with NULL in the external loop, and the
external loop will have a new condition to loop while that cursor is NULL.

My logic is that we can only 'break' when we are iterating over an object in the
internal loop. If we're iterating over an object in that loop then 'node != NULL'.

This way, if we broke from within the internal loop, the external loop will see
node as not NULL, and so it will stop looping itself. On the other hand, if the
internal loop has actually ended, then node will be NULL, and the outer loop
will keep running.

Is there anything I've missed?


Thanks,
Sasha
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