Date: Thu, 5 Mar 2009 18:29:22 +0900
To: jens.axboe@oracle.com
Cc: tglx@linutronix.de, James.Bottomley@HansenPartnership.com,
       jengelh@medozas.de, bharrosh@panasas.com, linux-scsi@vger.kernel.org,
       linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org
Subject: Re: [BUG] 2.6.29-rc6-2450cf in scsi_lib.c (was: Large amount of
	scsi-sgpool)objects
From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
In-Reply-To: <20090305173952U.fujita.tomonori@lab.ntt.co.jp>
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	<20090305173649M.fujita.tomonori@lab.ntt.co.jp>
	<20090305173952U.fujita.tomonori@lab.ntt.co.jp>
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Oops, somehow I forgot to CC Jens...

On Thu, 5 Mar 2009 17:39:17 +0900
FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:

> On Thu, 5 Mar 2009 17:36:13 +0900
> FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:
> 
> > CC'ed Jens,
> > 
> > On Wed, 04 Mar 2009 22:56:29 +0000
> > James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
> > 
> > > On Wed, 2009-03-04 at 22:45 +0100, Thomas Gleixner wrote:
> > > > On Wed, 4 Mar 2009, Thomas Gleixner wrote:
> > > > 
> > > > Instrumented the code and the result of the failing request is
> > > > below. Looks like the function which sets up the request gets
> > > > nr_phys_segments wrong by one. 
> > > > 
> > > > If you need further trace data feel free to ask.
> > > 
> > > OK, the mapping all checks out correctly ... there must be something
> > > wrong with the way we count before mapping.
> > 
> > Yeah, looks we miscalculate nr_phys_segments in the merging path.
> > 
> > blk_recount_segments() needs to set bi_seg_front_size and
> > bi_seg_back_size for ll_merge_requests_fn()?
> > 
> > =
> > diff --git a/block/blk-merge.c b/block/blk-merge.c
> > index a104593..efb65b6 100644
> > --- a/block/blk-merge.c
> > +++ b/block/blk-merge.c
> > @@ -111,12 +111,19 @@ void blk_recalc_rq_segments(struct request *rq)
> >  
> >  void blk_recount_segments(struct request_queue *q, struct bio *bio)
> >  {
> > +	unsigned int seg_size;
> >  	struct bio *nxt = bio->bi_next;
> >  
> >  	bio->bi_next = NULL;
> > -	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, NULL);
> > +	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, &seg_size);
> >  	bio->bi_next = nxt;
> >  	bio->bi_flags |= (1 << BIO_SEG_VALID);
> > +
> > +	if (bio->bi_phys_segments == 1 && seg_size > bio->bi_seg_front_size)
> > +		bio->bi_seg_front_size = seg_size;
> > +	if (bio->bi_phys_segments > bio->bi_seg_back_size)
> > +		bio->bi_seg_back_size = seg_size;
> > +
> >  }
> >  EXPORT_SYMBOL(blk_recount_segments);
> 
> Duh, here's the proper patch.
> 
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index a104593..06e0db4 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -111,12 +111,19 @@ void blk_recalc_rq_segments(struct request *rq)
>  
>  void blk_recount_segments(struct request_queue *q, struct bio *bio)
>  {
> +	unsigned int seg_size;
>  	struct bio *nxt = bio->bi_next;
>  
>  	bio->bi_next = NULL;
> -	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, NULL);
> +	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, &seg_size);
>  	bio->bi_next = nxt;
>  	bio->bi_flags |= (1 << BIO_SEG_VALID);
> +
> +	if (bio->bi_phys_segments == 1 && seg_size > bio->bi_seg_front_size)
> +		bio->bi_seg_front_size = seg_size;
> +	if (seg_size > bio->bi_seg_back_size)
> +		bio->bi_seg_back_size = seg_size;
> +
>  }
>  EXPORT_SYMBOL(blk_recount_segments);
>  
> --
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