On Thu, Mar 05 2009, FUJITA Tomonori wrote:
> Oops, somehow I forgot to CC Jens...
>
> On Thu, 5 Mar 2009 17:39:17 +0900
> FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote:
>
> > On Thu, 5 Mar 2009 17:36:13 +0900
> > FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote:
> >
> > > CC'ed Jens,
> > >
> > > On Wed, 04 Mar 2009 22:56:29 +0000
> > > James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> 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);
Good catch, I merged it with a slight change of layout and clearing
seg_size initially, to avoid gcc silly errors.
--
Jens Axboe
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