block: save page offset gaps in cloned bio

The cloned bio needs to inherit the accumulated gaps between vectors so
that we can know if this bio can subscribe to the iova coalescing
optimization.

When cloning for a split, the gap only applies to the front bio since
that's as far as has been processed. The remaining bio can reset its
gaps to 0 since it advanced past the checked vectors, and will start its
accounting from there on the next split check.

Fixes: 2f6b2565d43c ("block: accumulate memory segment gaps per bio")
Reported-by: Eric Auger <eauger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260819154937.3903312-1-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 9 insertions, 0 deletions

diff --git a/block/bio.c b/block/bio.c
index 898b2f5ef8c8..f95b63c0604a 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -859,6 +859,7 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
 	bio->bi_ioprio = bio_src->bi_ioprio;
 	bio->bi_write_hint = bio_src->bi_write_hint;
 	bio->bi_write_stream = bio_src->bi_write_stream;
+	bio->bi_bvec_gap_bit = bio_src->bi_bvec_gap_bit;
 	bio->bi_iter = bio_src->bi_iter;
 	bio->bi_io_vec = bio_src->bi_io_vec;
 
@@ -1972,6 +1973,14 @@ struct bio *bio_split(struct bio *bio, int sectors,
 
 	bio_advance(bio, split->bi_iter.bi_size);
 
+	/*
+	 * The gap bit is set when splitting to limits and only applies to the
+	 * front bio that was split off. The remaining bio will calcualte its
+	 * gap value when it is subsequently split to limits, so it is safe to
+	 * re-initialize the value back to 0.
+	 */
+	bio->bi_bvec_gap_bit = 0;
+
 	if (bio_flagged(bio, BIO_TRACE_COMPLETION))
 		bio_set_flag(split, BIO_TRACE_COMPLETION);