Re: [PATCH V11 14/19] block: handle non-cluster bio out of blk_bio_segment_split

Christoph Hellwig
2018-11-21T14:34:08Z

> + non-cluster.o

Do we really need a new source file for these few functions?

> default:
> + if (!blk_queue_cluster(q)) {
> + blk_queue_non_cluster_bio(q, bio);
> + return;

I'd name this blk_bio_segment_split_singlepage or similar.

> +static __init int init_non_cluster_bioset(void)
> +{
> + WARN_ON(bioset_init(&non_cluster_bio_set, BIO_POOL_SIZE, 0,
> + BIOSET_NEED_BVECS));
> + WARN_ON(bioset_integrity_create(&non_cluster_bio_set, BIO_POOL_SIZE));
> + WARN_ON(bioset_init(&non_cluster_bio_split, BIO_POOL_SIZE, 0, 0));

Please only allocate the resources once a queue without the cluster
flag is registered, there are only very few modern drivers that do that.

> +static void non_cluster_end_io(struct bio *bio)
> +{
> + struct bio *bio_orig = bio->bi_private;
> +
> + bio_orig->bi_status = bio->bi_status;
> + bio_endio(bio_orig);
> + bio_put(bio);
> +}

Why can't we use bio_chain for the split bios?

> + bio_for_each_segment(from, *bio_orig, iter) {
> + if (i++ < max_segs)
> + sectors += from.bv_len >> 9;
> + else
> + break;
> + }

The easy to read way would be:

bio_for_each_segment(from, *bio_orig, iter) {
if (i++ == max_segs)
break;
sectors += from.bv_len >> 9;
}

> + if (sectors < bio_sectors(*bio_orig)) {
> + bio = bio_split(*bio_orig, sectors, GFP_NOIO,
> + &non_cluster_bio_split);
> + bio_chain(bio, *bio_orig);
> + generic_make_request(*bio_orig);
> + *bio_orig = bio;

I don't think this is very efficient, as this means we now
clone the bio twice, first to split it at the sector boundary,
and then again when converting it to single-page bio_vec.

I think this could be something like this (totally untested):

diff --git a/block/non-cluster.c b/block/non-cluster.c
index 9c2910be9404..60389f275c43 100644
--- a/block/non-cluster.c
+++ b/block/non-cluster.c
@@ -13,58 +13,59 @@

#include "blk.h"

-static struct bio_set non_cluster_bio_set, non_cluster_bio_split;
+static struct bio_set non_cluster_bio_set;

static __init int init_non_cluster_bioset(void)
{
WARN_ON(bioset_init(&non_cluster_bio_set, BIO_POOL_SIZE, 0,
BIOSET_NEED_BVECS));
WARN_ON(bioset_integrity_create(&non_cluster_bio_set, BIO_POOL_SIZE));
- WARN_ON(bioset_init(&non_cluster_bio_split, BIO_POOL_SIZE, 0, 0));

return 0;
}
__initcall(init_non_cluster_bioset);

-static void non_cluster_end_io(struct bio *bio)
-{
- struct bio *bio_orig = bio->bi_private;
-
- bio_orig->bi_status = bio->bi_status;
- bio_endio(bio_orig);
- bio_put(bio);
-}
-
void blk_queue_non_cluster_bio(struct request_queue *q, struct bio **bio_orig)
{
- struct bio *bio;
struct bvec_iter iter;
- struct bio_vec from;
- unsigned i = 0;
- unsigned sectors = 0;
- unsigned short max_segs = min_t(unsigned short, BIO_MAX_PAGES,
- queue_max_segments(q));
+ struct bio *bio;
+ struct bio_vec bv;
+ unsigned short max_segs, segs = 0;
+
+ bio = bio_alloc_bioset(GFP_NOIO, bio_segments(*bio_orig),
+ &non_cluster_bio_set);
+ bio->bi_disk = (*bio_orig)->bi_disk;
+ bio->bi_partno = (*bio_orig)->bi_partno;
+ bio_set_flag(bio, BIO_CLONED);
+ if (bio_flagged(*bio_orig, BIO_THROTTLED))
+ bio_set_flag(bio, BIO_THROTTLED);
+ bio->bi_opf = (*bio_orig)->bi_opf;
+ bio->bi_ioprio = (*bio_orig)->bi_ioprio;
+ bio->bi_write_hint = (*bio_orig)->bi_write_hint;
+ bio->bi_iter.bi_sector = (*bio_orig)->bi_iter.bi_sector;
+ bio->bi_iter.bi_size = (*bio_orig)->bi_iter.bi_size;
+
+ if (bio_integrity(*bio_orig))
+ bio_integrity_clone(bio, *bio_orig, GFP_NOIO);

- bio_for_each_segment(from, *bio_orig, iter) {
- if (i++ < max_segs)
- sectors += from.bv_len >> 9;
- else
+ bio_clone_blkcg_association(bio, *bio_orig);
+
+ max_segs = min_t(unsigned short, queue_max_segments(q), BIO_MAX_PAGES);
+ bio_for_each_segment(bv, *bio_orig, iter) {
+ bio->bi_io_vec[segs++] = bv;
+ if (segs++ == max_segs)
break;
}

- if (sectors < bio_sectors(*bio_orig)) {
- bio = bio_split(*bio_orig, sectors, GFP_NOIO,
- &non_cluster_bio_split);
- bio_chain(bio, *bio_orig);
- generic_make_request(*bio_orig);
- *bio_orig = bio;
- }
- bio = bio_clone_bioset(*bio_orig, GFP_NOIO, &non_cluster_bio_set);
+ bio->bi_vcnt = segs;
+ bio->bi_phys_segments = segs;
+ bio_set_flag(bio, BIO_SEG_VALID);
+ bio_chain(bio, *bio_orig);

- bio->bi_phys_segments = bio_segments(bio);
- bio_set_flag(bio, BIO_SEG_VALID);
- bio->bi_end_io = non_cluster_end_io;
+ if (bio_integrity(bio))
+ bio_integrity_trim(bio);
+ bio_advance(bio, (*bio_orig)->bi_iter.bi_size);

- bio->bi_private = *bio_orig;
+ generic_make_request(*bio_orig);
*bio_orig = bio;
}