On Wed, 6 Jan 2016 05:51:34 +0000
Keith Busch <keith.busch@xxxxxxxxx> wrote:
> On Wed, Jan 06, 2016 at 10:17:51AM +0800, Ming Lei wrote:
>
> But this patch was to split on stripe boundaries, which is an even worse
> penalty if we get the split wrong.
>
> > + bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags);
> >
> > bio_for_each_segment(bv, bio, iter) {
> > - if (sectors + (bv.bv_len >> 9) > blk_max_size_offset(q, bio->bi_iter.bi_sector))
> > + if (no_sg_merge)
> > + goto new_segment;
>
> Bad idea for NVMe. We need to split on SG gaps, which you've skipped,
> or you will BUG_ON in the NVMe driver.
Given it is close to v4.4 release, I propose the following fix instead
of the bvec splitting approach, which is not ready in current block stack.
-----
block/blk-merge.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/block/blk-merge.c b/block/blk-merge.c
index e73846a..9ffe431 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -81,8 +81,16 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
struct bio *new = NULL;
bio_for_each_segment(bv, bio, iter) {
- if (sectors + (bv.bv_len >> 9) > blk_max_size_offset(q, bio->bi_iter.bi_sector))
+ if (sectors + (bv.bv_len >> 9) > blk_max_size_offset(q,
+ bio->bi_iter.bi_sector)) {
+ /*
+ * avoid to split out zero length bio if size to
+ * chunk boundary is too small
+ */
+ if (!sectors)
+ goto new_segment;
goto split;
+ }
/*
* If the queue doesn't support SG gaps and adding this
--
1.9.1
--
To unsubscribe from this list: send the line "unsubscribe linux-block" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
