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

From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: Pedro Alves <palves@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>,
	torvalds@linux-foundation.org, akpm@linux-foundation.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	paul.gortmaker@windriver.com, davem@davemloft.net, mingo@elte.hu,
	ebiederm@xmission.com, aarcange@redhat.com, ericvh@gmail.com,
	netdev@vger.kernel.org, josh@joshtriplett.org,
	eric.dumazet@gmail.com, axboe@kernel.dk, agk@redhat.com,
	dm-devel@redhat.com, neilb@suse.de, ccaulfie@redhat.com,
	teigland@redhat.com, Trond.Myklebust@netapp.com,
	bfields@fieldses.org, fweisbec@gmail.com, jesse@nicira.com,
	venkat.x.venkatsubra@oracle.com, ejt@redhat.com,
	snitzer@redhat.com, edumazet@google.com,
	linux-nfs@vger.kernel.org, dev@openvswitch.org,
	rds-devel@oss.oracle.com, lw@cn.fujitsu.com
Subject: Re: [PATCH v3 01/17] hashtable: introduce a small and naive hashtable
Date: Thu, 6 Sep 2012 10:33:20 -0400	[thread overview]
Message-ID: <20120906143320.GA4513@Krystal> (raw)
In-Reply-To: <5048AAF6.5090101@gmail.com>

* Sasha Levin (levinsasha928@gmail.com) wrote:
> 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?

This sounds good. Unless I'm missing something too.

Thanks!

Mathieu

> 
> 
> Thanks,
> Sasha

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