| Message ID | 20181126211946.77067-6-dennis@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: always associate blkg and refcount cleanup | expand |
On Mon, Nov 26, 2018 at 04:19:38PM -0500, Dennis Zhou wrote: > diff --git a/include/linux/bio.h b/include/linux/bio.h > index 62715a5a4f32..8bc9d9b29fd3 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -486,6 +486,12 @@ extern unsigned int bvec_nr_vecs(unsigned short idx); > extern const char *bio_devname(struct bio *bio, char *buffer); > > #define bio_set_dev(bio, bdev) \ > +do { \ > + bio_set_dev_only(bio, bdev); \ > + bio_associate_blkg(bio); \ > +} while (0) > + > +#define bio_set_dev_only(bio, bdev) \ > do { \ > if ((bio)->bi_disk != (bdev)->bd_disk) \ > bio_clear_flag(bio, BIO_THROTTLED);\ Generally looks okay to me but I'm not sure about bio_set_dev_only(). Maybe sth more explicit like bio_set_dev_without_blkg()? Also, can you please add comments explaining which should be used when? Thanks.
On Thu, Nov 29, 2018 at 07:53:33AM -0800, Tejun Heo wrote: > On Mon, Nov 26, 2018 at 04:19:38PM -0500, Dennis Zhou wrote: > > diff --git a/include/linux/bio.h b/include/linux/bio.h > > index 62715a5a4f32..8bc9d9b29fd3 100644 > > --- a/include/linux/bio.h > > +++ b/include/linux/bio.h > > @@ -486,6 +486,12 @@ extern unsigned int bvec_nr_vecs(unsigned short idx); > > extern const char *bio_devname(struct bio *bio, char *buffer); > > > > #define bio_set_dev(bio, bdev) \ > > +do { \ > > + bio_set_dev_only(bio, bdev); \ > > + bio_associate_blkg(bio); \ > > +} while (0) > > + > > +#define bio_set_dev_only(bio, bdev) \ > > do { \ > > if ((bio)->bi_disk != (bdev)->bd_disk) \ > > bio_clear_flag(bio, BIO_THROTTLED);\ > > Generally looks okay to me but I'm not sure about bio_set_dev_only(). > Maybe sth more explicit like bio_set_dev_without_blkg()? Also, can > you please add comments explaining which should be used when? > I've switched it to bio_set_dev_without_blkg() and added the comment below and added a comment in the use cases. Let me know if the wording is fine below. +/* + * Bio device setters. A blkg represents the relationship between a blkcg + * and a request_queue. When the device is set for a bio, it becomes possible + * to do blkg association. Importantly, a blkg also holds a pointer back to + * the request_queue. In general, bio_set_dev() should be used to keep + * bio->bi_disk->queue and bio->bi_blkg->q consistent. If blkg association + * will be done explicitly or is a bio based device, use + * bio_set_dev_without_blkg(). + */ Thanks, Dennis
> diff --git a/include/linux/bio.h b/include/linux/bio.h > index 62715a5a4f32..8bc9d9b29fd3 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -486,6 +486,12 @@ extern unsigned int bvec_nr_vecs(unsigned short idx); > extern const char *bio_devname(struct bio *bio, char *buffer); > > #define bio_set_dev(bio, bdev) \ > +do { \ > + bio_set_dev_only(bio, bdev); \ > + bio_associate_blkg(bio); \ > +} while (0) > + > +#define bio_set_dev_only(bio, bdev) \ This lacks any explanation on when you would use bio_set_dev_only or bio_set_dev. Please document why we need both and why you'd choose or the other.
On Fri, Nov 30, 2018 at 01:54:26AM -0800, Christoph Hellwig wrote: > > diff --git a/include/linux/bio.h b/include/linux/bio.h > > index 62715a5a4f32..8bc9d9b29fd3 100644 > > --- a/include/linux/bio.h > > +++ b/include/linux/bio.h > > @@ -486,6 +486,12 @@ extern unsigned int bvec_nr_vecs(unsigned short idx); > > extern const char *bio_devname(struct bio *bio, char *buffer); > > > > #define bio_set_dev(bio, bdev) \ > > +do { \ > > + bio_set_dev_only(bio, bdev); \ > > + bio_associate_blkg(bio); \ > > +} while (0) > > + > > +#define bio_set_dev_only(bio, bdev) \ > > This lacks any explanation on when you would use bio_set_dev_only or > bio_set_dev. Please document why we need both and why you'd choose or > the other. I realized after thinking about this more and checking more use cases that it isn't as simple as swapping macro uses because many of the callers share common bio allocation paths. I think the simplest way forward is to have writeback and swap do reassociation and split out bio init code in a future series. So in v5, there is only bio_set_dev(). Thanks, Dennis
diff --git a/block/bio.c b/block/bio.c index de0133329b71..929fd3692e4a 100644 --- a/block/bio.c +++ b/block/bio.c @@ -2092,6 +2092,7 @@ void bio_associate_blkg(struct bio *bio) rcu_read_unlock(); } +EXPORT_SYMBOL_GPL(bio_associate_blkg); /** * bio_disassociate_task - undo bio_associate_current() diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c index cdbd10564e66..e6b47c255521 100644 --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -472,14 +472,12 @@ static void check_scale_change(struct iolatency_grp *iolat) static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) { struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); - struct blkcg_gq *blkg; + struct blkcg_gq *blkg = bio->bi_blkg; bool issue_as_root = bio_issue_as_root_blkg(bio); if (!blk_iolatency_enabled(blkiolat)) return; - bio_associate_blkg(bio); - blkg = bio->bi_blkg; bio_issue_init(&bio->bi_issue, bio_sectors(bio)); while (blkg && blkg->parent) { diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 228c3a007ebc..1c6529df2002 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -2118,7 +2118,6 @@ static inline void throtl_update_latency_buckets(struct throtl_data *td) static void blk_throtl_assoc_bio(struct bio *bio) { #ifdef CONFIG_BLK_DEV_THROTTLING_LOW - bio_associate_blkg(bio); bio_issue_init(&bio->bi_issue, bio_sectors(bio)); #endif } diff --git a/fs/buffer.c b/fs/buffer.c index 1286c2b95498..9661e5be87e2 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -3066,7 +3066,7 @@ static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh, } bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9); - bio_set_dev(bio, bh->b_bdev); + bio_set_dev_only(bio, bh->b_bdev); bio->bi_write_hint = write_hint; bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh)); diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c index db7590178dfc..cadf91a42fa5 100644 --- a/fs/ext4/page-io.c +++ b/fs/ext4/page-io.c @@ -376,7 +376,7 @@ static int io_submit_init_bio(struct ext4_io_submit *io, return -ENOMEM; wbc_init_bio(io->io_wbc, bio); bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9); - bio_set_dev(bio, bh->b_bdev); + bio_set_dev_only(bio, bh->b_bdev); bio->bi_end_io = ext4_end_bio; bio->bi_private = ext4_get_io_end(io->io_end); io->io_bio = bio; diff --git a/include/linux/bio.h b/include/linux/bio.h index 62715a5a4f32..8bc9d9b29fd3 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -486,6 +486,12 @@ extern unsigned int bvec_nr_vecs(unsigned short idx); extern const char *bio_devname(struct bio *bio, char *buffer); #define bio_set_dev(bio, bdev) \ +do { \ + bio_set_dev_only(bio, bdev); \ + bio_associate_blkg(bio); \ +} while (0) + +#define bio_set_dev_only(bio, bdev) \ do { \ if ((bio)->bi_disk != (bdev)->bd_disk) \ bio_clear_flag(bio, BIO_THROTTLED);\ @@ -497,6 +503,7 @@ do { \ do { \ (dst)->bi_disk = (src)->bi_disk; \ (dst)->bi_partno = (src)->bi_partno; \ + bio_clone_blkcg_association(dst, src); \ } while (0) #define bio_dev(bio) \ diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index 9d796a4f8ef0..81b45943ce29 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -802,21 +802,19 @@ static inline bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg static inline bool blkcg_bio_issue_check(struct request_queue *q, struct bio *bio) { - struct blkcg *blkcg; struct blkcg_gq *blkg; bool throtl = false; rcu_read_lock(); - /* associate blkcg if bio hasn't attached one */ - bio_associate_blkcg(bio, NULL); - blkcg = bio_blkcg(bio); - blkg = blkg_lookup_create(blkcg, q); + if (!bio->bi_blkg) + bio_associate_blkg(bio); + + blkg = bio->bi_blkg; throtl = blk_throtl_bio(q, blkg, bio); if (!throtl) { - blkg = blkg ?: q->root_blkg; /* * If the bio is flagged with BIO_QUEUE_ENTERED it means this * is a split bio and we would have already accounted for the diff --git a/mm/page_io.c b/mm/page_io.c index 5bdfd21c1bd9..257fdd67308d 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -37,7 +37,7 @@ static struct bio *get_swap_bio(gfp_t gfp_flags, struct block_device *bdev; bio->bi_iter.bi_sector = map_swap_page(page, &bdev); - bio_set_dev(bio, bdev); + bio_set_dev_only(bio, bdev); bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9; bio->bi_end_io = end_io;
Previously, blkg association was handled by controller specific code in blk-throttle and blk-iolatency. However, because a blkg represents a relationship between a blkcg and a request_queue, it makes sense to keep the blkg->q and bio->bi_disk->queue consistent. This patch moves association into the bio_set_dev macro. This should cover the majority of cases where the device is set/changed keeping the two pointers consistent. Fallback code is added to blkcg_bio_issue_check() to catch any missing paths. The check is safe here because bio->bi_disk->queue must exist for a request to have made it to generic_make_request_checks(). Signed-off-by: Dennis Zhou <dennis@kernel.org> --- block/bio.c | 1 + block/blk-iolatency.c | 4 +--- block/blk-throttle.c | 1 - fs/buffer.c | 2 +- fs/ext4/page-io.c | 2 +- include/linux/bio.h | 7 +++++++ include/linux/blk-cgroup.h | 10 ++++------ mm/page_io.c | 2 +- 8 files changed, 16 insertions(+), 13 deletions(-)