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);
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