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From: Ingo Molnar <mingo@elte.hu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jens Axboe <jens.axboe@oracle.com>,
	linux-kernel@vger.kernel.org, Alan.Brunelle@hp.com,
	arjan@linux.intel.com, dgc@sgi.com, npiggin@suse.de,
	Andrew Morton <akpm@linux-foundation.org>,
	Vegard Nossum <vegard.nossum@gmail.com>,
	Pekka Enberg <penberg@gmail.com>
Subject: Re: [patch] block layer: kmemcheck fixes
Date: Thu, 7 Feb 2008 20:31:40 +0100	[thread overview]
Message-ID: <20080207193140.GA19949@elte.hu> (raw)
In-Reply-To: <alpine.LFD.1.00.0802070940230.2883@woody.linux-foundation.org>


* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Thu, 7 Feb 2008, Ingo Molnar wrote:
> >  	INIT_HLIST_NODE(&rq->hash);
> >  	RB_CLEAR_NODE(&rq->rb_node);
> > -	rq->ioprio = 0;
> > -	rq->buffer = NULL;
> > -	rq->ref_count = 1;
> > -	rq->q = q;
> > -	rq->special = NULL;
> > -	rq->data_len = 0;
> > -	rq->data = NULL;
> > -	rq->nr_phys_segments = 0;
> > -	rq->sense = NULL;
> > -	rq->end_io = NULL;
> > -	rq->end_io_data = NULL;
> > -	rq->completion_data = NULL;
> > -	rq->next_rq = NULL;
> > +	rq->completion_data		= NULL;
> > +	/* rq->elevator_private			*/
> > +	/* rq->elevator_private2		*/
> > +	/* rq->rq_disk				*/
> > +	/* rq->start_time			*/
> > +	rq->nr_phys_segments		= 0;
> > +	/* rq->nr_hw_segments			*/
> > +	rq->ioprio			= 0;
> > +	rq->special			= NULL;
> > +	rq->buffer			= NULL;
> ...
> 
> Can we please just stop doing these one-by-one assignments, and just do 
> something like
> 
> 	memset(rq, 0, sizeof(*rq));
> 	rq->q = q;
> 	rq->ref_count = 1;
> 	INIT_HLIST_NODE(&rq->hash);
> 	RB_CLEAR_NODE(&rq->rb_node);
> 
> instead?
> 
> The memset() is likely faster and smaller than one-by-one assignments 
> anyway, even if the one-by-ones can avoid initializing some field or 
> there ends up being a double initialization..

i definitely agree and do that for all code i write.

But if someone does item by item initialization for some crazy 
performance reason (networking folks tend to have such constructs), it 
should be done i think how i've done it in the patch: by systematically 
listing _every_ field in the structure, in the same order, and 
indicating it clearly when it is not initialized and why.

and there it already shows that we do not initialize a few other members 
that could cause problems later on:

+       rq->data_len                    = 0;
+       /* rq->sense_len                        */
+       rq->data                        = NULL;
+       rq->sense                       = NULL;

why is sense_len not initialized - while data_len is? In any case, these 
days the memclear instructions are dirt cheap and we should just always 
initialize everything to zero by default, especially if it's almost all 
zero-initialized anyway.

	Ingo

  parent reply	other threads:[~2008-02-07 19:32 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-07  9:18 [PATCH 0/8] IO queuing and complete affinity Jens Axboe
2008-02-07  9:18 ` [PATCH 1/8] block: split softirq handling into blk-softirq.c Jens Axboe
2008-02-07  9:18 ` [PATCH 2/8] Add interface for queuing work on a specific CPU Jens Axboe
2008-02-07  9:45   ` Andrew Morton
2008-02-07  9:49     ` Jens Axboe
2008-02-07 17:44       ` Harvey Harrison
2008-02-11 10:51     ` Oleg Nesterov
2008-02-07  9:19 ` [PATCH 3/8] block: make kblockd_schedule_work() take the queue as parameter Jens Axboe
2008-02-07  9:19 ` [PATCH 4/8] x86: add support for remotely triggering the block softirq Jens Axboe
2008-02-07 10:07   ` Ingo Molnar
2008-02-07 10:17     ` Jens Axboe
2008-02-07 10:25       ` Ingo Molnar
2008-02-07 10:31         ` Jens Axboe
2008-02-07 10:38           ` Ingo Molnar
2008-02-07 14:18             ` Jens Axboe
2008-02-07 10:49           ` [patch] block layer: kmemcheck fixes Ingo Molnar
2008-02-07 17:42             ` Linus Torvalds
2008-02-07 17:55               ` Jens Axboe
2008-02-07 19:31               ` Ingo Molnar [this message]
2008-02-07 20:06                 ` Jens Axboe
2008-02-08  1:22               ` David Miller
2008-02-08  1:28                 ` Linus Torvalds
2008-02-08 15:09                 ` Arjan van de Ven
2008-02-08 22:44                   ` Nick Piggin
2008-02-08 22:56                     ` Arjan van de Ven
2008-02-08 23:58                       ` Nick Piggin
2008-02-08 11:38               ` Jens Axboe
2008-02-07  9:19 ` [PATCH 5/8] x86-64: add support for remotely triggering the block softirq Jens Axboe
2008-02-07  9:19 ` [PATCH 6/8] ia64: " Jens Axboe
2008-02-07  9:19 ` [PATCH 7/8] kernel: add generic softirq interface for triggering a remote softirq Jens Axboe
2008-02-07  9:19 ` [PATCH 8/8] block: add test code for testing CPU affinity Jens Axboe
2008-02-07 15:16 ` [PATCH 0/8] IO queuing and complete affinity Alan D. Brunelle
2008-02-07 18:25 ` IO queuing and complete affinity with threads (was Re: [PATCH 0/8] IO queuing and complete affinity) Jens Axboe
2008-02-07 20:40   ` Alan D. Brunelle
2008-02-08  7:38   ` Nick Piggin
2008-02-08  7:47     ` Jens Axboe
2008-02-08  7:53       ` Nick Piggin
2008-02-08  7:59         ` Jens Axboe
2008-02-08  8:12           ` Nick Piggin
2008-02-08  8:24             ` Jens Axboe
2008-02-08  8:33               ` Nick Piggin
2008-02-11  5:22           ` David Chinner
2008-02-12  8:28             ` Jeremy Higdon

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