return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs);
}
+static inline unsigned get_max_io_size(struct request_queue *q,
+ struct bio *bio)
+{
+ unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
+ unsigned mask = queue_logical_block_size(q) - 1;
+
+ /* aligned to logical block size */
+ sectors &= ~(mask >> 9);
+
+ return sectors;
+}
+
static struct bio *blk_bio_segment_split(struct request_queue *q,
struct bio *bio,
struct bio_set *bs,
struct bio_vec bv, bvprv, *bvprvp = NULL;
struct bvec_iter iter;
unsigned seg_size = 0, nsegs = 0, sectors = 0;
+ unsigned front_seg_size = bio->bi_seg_front_size;
+ bool do_split = true;
+ struct bio *new = NULL;
+ const unsigned max_sectors = get_max_io_size(q, bio);
+ unsigned bvecs = 0;
bio_for_each_segment(bv, bio, iter) {
- if (sectors + (bv.bv_len >> 9) > queue_max_sectors(q))
+ /*
+ * With arbitrary bio size, the incoming bio may be very
+ * big. We have to split the bio into small bios so that
+ * each holds at most BIO_MAX_PAGES bvecs because
+ * bio_clone() can fail to allocate big bvecs.
+ *
+ * It should have been better to apply the limit per
+ * request queue in which bio_clone() is involved,
+ * instead of globally. The biggest blocker is the
+ * bio_clone() in bio bounce.
+ *
+ * If bio is splitted by this reason, we should have
+ * allowed to continue bios merging, but don't do
+ * that now for making the change simple.
+ *
+ * TODO: deal with bio bounce's bio_clone() gracefully
+ * and convert the global limit into per-queue limit.
+ */
+ if (bvecs++ >= BIO_MAX_PAGES)
goto split;
/*
if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset))
goto split;
+ if (sectors + (bv.bv_len >> 9) > max_sectors) {
+ /*
+ * Consider this a new segment if we're splitting in
+ * the middle of this vector.
+ */
+ if (nsegs < queue_max_segments(q) &&
+ sectors < max_sectors) {
+ nsegs++;
+ sectors = max_sectors;
+ }
+ if (sectors)
+ goto split;
+ /* Make this single bvec as the 1st segment */
+ }
+
if (bvprvp && blk_queue_cluster(q)) {
if (seg_size + bv.bv_len > queue_max_segment_size(q))
goto new_segment;
seg_size += bv.bv_len;
bvprv = bv;
- bvprvp = &bv;
+ bvprvp = &bvprv;
sectors += bv.bv_len >> 9;
+
+ if (nsegs == 1 && seg_size > front_seg_size)
+ front_seg_size = seg_size;
continue;
}
new_segment:
nsegs++;
bvprv = bv;
- bvprvp = &bv;
+ bvprvp = &bvprv;
seg_size = bv.bv_len;
sectors += bv.bv_len >> 9;
+
+ if (nsegs == 1 && seg_size > front_seg_size)
+ front_seg_size = seg_size;
}
- *segs = nsegs;
- return NULL;
+ do_split = false;
split:
*segs = nsegs;
- return bio_split(bio, sectors, GFP_NOIO, bs);
+
+ if (do_split) {
+ new = bio_split(bio, sectors, GFP_NOIO, bs);
+ if (new)
+ bio = new;
+ }
+
+ bio->bi_seg_front_size = front_seg_size;
+ if (seg_size > bio->bi_seg_back_size)
+ bio->bi_seg_back_size = seg_size;
+
+ return do_split ? new : NULL;
}
void blk_queue_split(struct request_queue *q, struct bio **bio,
if (sg)
sg_mark_end(sg);
+ /*
+ * Something must have been wrong if the figured number of
+ * segment is bigger than number of req's physical segments
+ */
+ WARN_ON(nsegs > rq->nr_phys_segments);
+
return nsegs;
}
EXPORT_SYMBOL(blk_rq_map_sg);