Re: bcache: remove driver private bio splitting code

[Eric Wheeler <bcache@lists.ewheeler.net>]

> From: Kent Overstreet Wed, 12 Aug 2015 00:07:13 -0700
> The bcache driver has always accepted arbitrarily large bios and split
> them internally.  Now that every driver must accept arbitrarily large
> bios this code isn't nessecary anymore.

Hi Kent,

Does your patch below make any kernel version assumptions about bio 
splitting?  That doesn't appear so based on the commit message, but 
thought I'd double-check.

If there is a kernel dependency, then, how far back should this be safe?  
I'd like to apply to 3.17-rc1 like the other stable commits and stamp it 
with Cc: stable@ so it will merge forward into 3.18 and onward if it fixes 
my problem below:

This question comes up because I'm getting the following 
(discard-related?) backtrace and would like to try the patch.  If it fixes 
the problem I'll stamp it with stable and get it to Jens.  Note that 
bch_generic_make_request() doesn't even exist after this patch, so this 
backtrace would at least be simplified and possibly fixed:

[  294.059255]  [<ffffffffa049a20d>] bch_generic_make_request+0x15d/0x1f0 [bcache]
[  294.059578]  [<ffffffffa049a3b9>] __bch_submit_bbio+0x79/0x80 [bcache]
[  294.059794]  [<ffffffffa049a3eb>] bch_submit_bbio+0x2b/0x30 [bcache]
[  294.059983]  [<ffffffffa049fabb>] bch_data_insert_start+0xcb/0x5a0 [bcache]
[  294.060169]  [<ffffffffa049ffe1>] bch_data_insert+0x51/0xc0 [bcache]
[  294.060354]  [<ffffffffa04a0cc4>] cached_dev_make_request+0xbe4/0xdf0 [bcache]
[  294.060652]  [<ffffffff81317c20>] generic_make_request+0xe0/0x130
[  294.060830]  [<ffffffff81317ce7>] submit_bio+0x77/0x150
[  294.061012]  [<ffffffff81312906>] ? bio_alloc_bioset+0x1d6/0x330
[  294.061194]  [<ffffffffa04cef90>] ? le64_dec+0x20/0x20 [dm_persistent_data]
[  294.061377]  [<ffffffffa04e49be>] __blkdev_issue_discard_async.constprop.59+0x17e/0x210 [dm_thin_pool]
[  294.061695]  [<ffffffffa04e55dc>] process_prepared_discard_passdown+0x9c/0x230 [dm_thin_pool]
[  294.062007]  [<ffffffff811ac73f>] ? mempool_free+0x2f/0x90
[  294.062207]  [<ffffffffa04e0772>] process_prepared+0x92/0xc0 [dm_thin_pool]
[  294.062404]  [<ffffffffa04e5f78>] do_worker+0xb8/0x880 [dm_thin_pool]
[  294.062606]  [<ffffffff81014693>] ? __switch_to+0x1e3/0x580
[  294.062796]  [<ffffffff810dc71c>] ? put_prev_task_fair+0x2c/0x40
[  294.062989]  [<ffffffff810ba18d>] process_one_work+0x14d/0x420
[  294.063171]  [<ffffffff810ba952>] worker_thread+0x112/0x520
[  294.063355]  [<ffffffff810ba840>] ? rescuer_thread+0x3e0/0x3e0
[  294.063560]  [<ffffffff810c06a8>] kthread+0xd8/0xf0
[  294.063737]  [<ffffffff810c05d0>] ? kthread_create_on_node+0x1b0/0x1b0
[  294.063943]  [<ffffffff816e4aa2>] ret_from_fork+0x42/0x70
[  294.064133]  [<ffffffff810c05d0>] ? kthread_create_on_node+0x1b0/0x1b0


Thanks!

-Eric
 
> Cc: linux-bcache@vger.kernel.org
> Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
> [dpark: add more description in commit message]
> Signed-off-by: Dongsu Park <dpark@posteo.net>
> Signed-off-by: Ming Lin <ming.l@ssi.samsung.com>
> ---
>  drivers/md/bcache/bcache.h    |  18 --------
>  drivers/md/bcache/io.c        | 101 +-----------------------------------------
>  drivers/md/bcache/journal.c   |   4 +-
>  drivers/md/bcache/request.c   |  16 +++----
>  drivers/md/bcache/super.c     |  32 +------------
>  drivers/md/bcache/util.h      |   5 ++-
>  drivers/md/bcache/writeback.c |   4 +-
>  7 files changed, 18 insertions(+), 162 deletions(-)
> 
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 04f7bc2..6b420a5 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -243,19 +243,6 @@ struct keybuf {
>  	DECLARE_ARRAY_ALLOCATOR(struct keybuf_key, freelist, KEYBUF_NR);
>  };
>  
> -struct bio_split_pool {
> -	struct bio_set		*bio_split;
> -	mempool_t		*bio_split_hook;
> -};
> -
> -struct bio_split_hook {
> -	struct closure		cl;
> -	struct bio_split_pool	*p;
> -	struct bio		*bio;
> -	bio_end_io_t		*bi_end_io;
> -	void			*bi_private;
> -};
> -
>  struct bcache_device {
>  	struct closure		cl;
>  
> @@ -288,8 +275,6 @@ struct bcache_device {
>  	int (*cache_miss)(struct btree *, struct search *,
>  			  struct bio *, unsigned);
>  	int (*ioctl) (struct bcache_device *, fmode_t, unsigned, unsigned long);
> -
> -	struct bio_split_pool	bio_split_hook;
>  };
>  
>  struct io {
> @@ -454,8 +439,6 @@ struct cache {
>  	atomic_long_t		meta_sectors_written;
>  	atomic_long_t		btree_sectors_written;
>  	atomic_long_t		sectors_written;
> -
> -	struct bio_split_pool	bio_split_hook;
>  };
>  
>  struct gc_stat {
> @@ -873,7 +856,6 @@ void bch_bbio_endio(struct cache_set *, struct bio *, int, const char *);
>  void bch_bbio_free(struct bio *, struct cache_set *);
>  struct bio *bch_bbio_alloc(struct cache_set *);
>  
> -void bch_generic_make_request(struct bio *, struct bio_split_pool *);
>  void __bch_submit_bbio(struct bio *, struct cache_set *);
>  void bch_submit_bbio(struct bio *, struct cache_set *, struct bkey *, unsigned);
>  
> diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
> index bf6a9ca..86a0bb8 100644
> --- a/drivers/md/bcache/io.c
> +++ b/drivers/md/bcache/io.c
> @@ -11,105 +11,6 @@
>  
>  #include <linux/blkdev.h>
>  
> -static unsigned bch_bio_max_sectors(struct bio *bio)
> -{
> -	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
> -	struct bio_vec bv;
> -	struct bvec_iter iter;
> -	unsigned ret = 0, seg = 0;
> -
> -	if (bio->bi_rw & REQ_DISCARD)
> -		return min(bio_sectors(bio), q->limits.max_discard_sectors);
> -
> -	bio_for_each_segment(bv, bio, iter) {
> -		struct bvec_merge_data bvm = {
> -			.bi_bdev	= bio->bi_bdev,
> -			.bi_sector	= bio->bi_iter.bi_sector,
> -			.bi_size	= ret << 9,
> -			.bi_rw		= bio->bi_rw,
> -		};
> -
> -		if (seg == min_t(unsigned, BIO_MAX_PAGES,
> -				 queue_max_segments(q)))
> -			break;
> -
> -		if (q->merge_bvec_fn &&
> -		    q->merge_bvec_fn(q, &bvm, &bv) < (int) bv.bv_len)
> -			break;
> -
> -		seg++;
> -		ret += bv.bv_len >> 9;
> -	}
> -
> -	ret = min(ret, queue_max_sectors(q));
> -
> -	WARN_ON(!ret);
> -	ret = max_t(int, ret, bio_iovec(bio).bv_len >> 9);
> -
> -	return ret;
> -}
> -
> -static void bch_bio_submit_split_done(struct closure *cl)
> -{
> -	struct bio_split_hook *s = container_of(cl, struct bio_split_hook, cl);
> -
> -	s->bio->bi_end_io = s->bi_end_io;
> -	s->bio->bi_private = s->bi_private;
> -	bio_endio(s->bio, 0);
> -
> -	closure_debug_destroy(&s->cl);
> -	mempool_free(s, s->p->bio_split_hook);
> -}
> -
> -static void bch_bio_submit_split_endio(struct bio *bio, int error)
> -{
> -	struct closure *cl = bio->bi_private;
> -	struct bio_split_hook *s = container_of(cl, struct bio_split_hook, cl);
> -
> -	if (error)
> -		clear_bit(BIO_UPTODATE, &s->bio->bi_flags);
> -
> -	bio_put(bio);
> -	closure_put(cl);
> -}
> -
> -void bch_generic_make_request(struct bio *bio, struct bio_split_pool *p)
> -{
> -	struct bio_split_hook *s;
> -	struct bio *n;
> -
> -	if (!bio_has_data(bio) && !(bio->bi_rw & REQ_DISCARD))
> -		goto submit;
> -
> -	if (bio_sectors(bio) <= bch_bio_max_sectors(bio))
> -		goto submit;
> -
> -	s = mempool_alloc(p->bio_split_hook, GFP_NOIO);
> -	closure_init(&s->cl, NULL);
> -
> -	s->bio		= bio;
> -	s->p		= p;
> -	s->bi_end_io	= bio->bi_end_io;
> -	s->bi_private	= bio->bi_private;
> -	bio_get(bio);
> -
> -	do {
> -		n = bio_next_split(bio, bch_bio_max_sectors(bio),
> -				   GFP_NOIO, s->p->bio_split);
> -
> -		n->bi_end_io	= bch_bio_submit_split_endio;
> -		n->bi_private	= &s->cl;
> -
> -		closure_get(&s->cl);
> -		generic_make_request(n);
> -	} while (n != bio);
> -
> -	continue_at(&s->cl, bch_bio_submit_split_done, NULL);
> -	return;
> -submit:
> -	generic_make_request(bio);
> -}
> -
>  /* Bios with headers */
>  
>  void bch_bbio_free(struct bio *bio, struct cache_set *c)
> @@ -139,7 +40,7 @@ void __bch_submit_bbio(struct bio *bio, struct cache_set *c)
>  	bio->bi_bdev		= PTR_CACHE(c, &b->key, 0)->bdev;
>  
>  	b->submit_time_us = local_clock_us();
> -	closure_bio_submit(bio, bio->bi_private, PTR_CACHE(c, &b->key, 0));
> +	closure_bio_submit(bio, bio->bi_private);
>  }
>  
>  void bch_submit_bbio(struct bio *bio, struct cache_set *c,
> diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
> index 418607a..727ca9b 100644
> --- a/drivers/md/bcache/journal.c
> +++ b/drivers/md/bcache/journal.c
> @@ -61,7 +61,7 @@ reread:		left = ca->sb.bucket_size - offset;
>  		bio->bi_private = &cl;
>  		bch_bio_map(bio, data);
>  
> -		closure_bio_submit(bio, &cl, ca);
> +		closure_bio_submit(bio, &cl);
>  		closure_sync(&cl);
>  
>  		/* This function could be simpler now since we no longer write
> @@ -648,7 +648,7 @@ static void journal_write_unlocked(struct closure *cl)
>  	spin_unlock(&c->journal.lock);
>  
>  	while ((bio = bio_list_pop(&list)))
> -		closure_bio_submit(bio, cl, c->cache[0]);
> +		closure_bio_submit(bio, cl);
>  
>  	continue_at(cl, journal_write_done, NULL);
>  }
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index f292790..ab093a8 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -718,7 +718,7 @@ static void cached_dev_read_error(struct closure *cl)
>  
>  		/* XXX: invalidate cache */
>  
> -		closure_bio_submit(bio, cl, s->d);
> +		closure_bio_submit(bio, cl);
>  	}
>  
>  	continue_at(cl, cached_dev_cache_miss_done, NULL);
> @@ -841,7 +841,7 @@ static int cached_dev_cache_miss(struct btree *b, struct search *s,
>  	s->cache_miss	= miss;
>  	s->iop.bio	= cache_bio;
>  	bio_get(cache_bio);
> -	closure_bio_submit(cache_bio, &s->cl, s->d);
> +	closure_bio_submit(cache_bio, &s->cl);
>  
>  	return ret;
>  out_put:
> @@ -849,7 +849,7 @@ out_put:
>  out_submit:
>  	miss->bi_end_io		= request_endio;
>  	miss->bi_private	= &s->cl;
> -	closure_bio_submit(miss, &s->cl, s->d);
> +	closure_bio_submit(miss, &s->cl);
>  	return ret;
>  }
>  
> @@ -914,7 +914,7 @@ static void cached_dev_write(struct cached_dev *dc, struct search *s)
>  
>  		if (!(bio->bi_rw & REQ_DISCARD) ||
>  		    blk_queue_discard(bdev_get_queue(dc->bdev)))
> -			closure_bio_submit(bio, cl, s->d);
> +			closure_bio_submit(bio, cl);
>  	} else if (s->iop.writeback) {
>  		bch_writeback_add(dc);
>  		s->iop.bio = bio;
> @@ -929,12 +929,12 @@ static void cached_dev_write(struct cached_dev *dc, struct search *s)
>  			flush->bi_end_io = request_endio;
>  			flush->bi_private = cl;
>  
> -			closure_bio_submit(flush, cl, s->d);
> +			closure_bio_submit(flush, cl);
>  		}
>  	} else {
>  		s->iop.bio = bio_clone_fast(bio, GFP_NOIO, dc->disk.bio_split);
>  
> -		closure_bio_submit(bio, cl, s->d);
> +		closure_bio_submit(bio, cl);
>  	}
>  
>  	closure_call(&s->iop.cl, bch_data_insert, NULL, cl);
> @@ -950,7 +950,7 @@ static void cached_dev_nodata(struct closure *cl)
>  		bch_journal_meta(s->iop.c, cl);
>  
>  	/* If it's a flush, we send the flush to the backing device too */
> -	closure_bio_submit(bio, cl, s->d);
> +	closure_bio_submit(bio, cl);
>  
>  	continue_at(cl, cached_dev_bio_complete, NULL);
>  }
> @@ -994,7 +994,7 @@ static void cached_dev_make_request(struct request_queue *q, struct bio *bio)
>  		    !blk_queue_discard(bdev_get_queue(dc->bdev)))
>  			bio_endio(bio, 0);
>  		else
> -			bch_generic_make_request(bio, &d->bio_split_hook);
> +			generic_make_request(bio);
>  	}
>  }
>  
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 94980bf..db70c9e 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -59,29 +59,6 @@ struct workqueue_struct *bcache_wq;
>  
>  #define BTREE_MAX_PAGES		(256 * 1024 / PAGE_SIZE)
>  
> -static void bio_split_pool_free(struct bio_split_pool *p)
> -{
> -	if (p->bio_split_hook)
> -		mempool_destroy(p->bio_split_hook);
> -
> -	if (p->bio_split)
> -		bioset_free(p->bio_split);
> -}
> -
> -static int bio_split_pool_init(struct bio_split_pool *p)
> -{
> -	p->bio_split = bioset_create(4, 0);
> -	if (!p->bio_split)
> -		return -ENOMEM;
> -
> -	p->bio_split_hook = mempool_create_kmalloc_pool(4,
> -				sizeof(struct bio_split_hook));
> -	if (!p->bio_split_hook)
> -		return -ENOMEM;
> -
> -	return 0;
> -}
> -
>  /* Superblock */
>  
>  static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
> @@ -537,7 +514,7 @@ static void prio_io(struct cache *ca, uint64_t bucket, unsigned long rw)
>  	bio->bi_private = ca;
>  	bch_bio_map(bio, ca->disk_buckets);
>  
> -	closure_bio_submit(bio, &ca->prio, ca);
> +	closure_bio_submit(bio, &ca->prio);
>  	closure_sync(cl);
>  }
>  
> @@ -757,7 +734,6 @@ static void bcache_device_free(struct bcache_device *d)
>  		put_disk(d->disk);
>  	}
>  
> -	bio_split_pool_free(&d->bio_split_hook);
>  	if (d->bio_split)
>  		bioset_free(d->bio_split);
>  	kvfree(d->full_dirty_stripes);
> @@ -804,7 +780,6 @@ static int bcache_device_init(struct bcache_device *d, unsigned block_size,
>  		return minor;
>  
>  	if (!(d->bio_split = bioset_create(4, offsetof(struct bbio, bio))) ||
> -	    bio_split_pool_init(&d->bio_split_hook) ||
>  	    !(d->disk = alloc_disk(1))) {
>  		ida_simple_remove(&bcache_minor, minor);
>  		return -ENOMEM;
> @@ -1793,8 +1768,6 @@ void bch_cache_release(struct kobject *kobj)
>  		ca->set->cache[ca->sb.nr_this_dev] = NULL;
>  	}
>  
> -	bio_split_pool_free(&ca->bio_split_hook);
> -
>  	free_pages((unsigned long) ca->disk_buckets, ilog2(bucket_pages(ca)));
>  	kfree(ca->prio_buckets);
>  	vfree(ca->buckets);
> @@ -1839,8 +1812,7 @@ static int cache_alloc(struct cache_sb *sb, struct cache *ca)
>  					  ca->sb.nbuckets)) ||
>  	    !(ca->prio_buckets	= kzalloc(sizeof(uint64_t) * prio_buckets(ca) *
>  					  2, GFP_KERNEL)) ||
> -	    !(ca->disk_buckets	= alloc_bucket_pages(GFP_KERNEL, ca)) ||
> -	    bio_split_pool_init(&ca->bio_split_hook))
> +	    !(ca->disk_buckets	= alloc_bucket_pages(GFP_KERNEL, ca)))
>  		return -ENOMEM;
>  
>  	ca->prio_last_buckets = ca->prio_buckets + prio_buckets(ca);
> diff --git a/drivers/md/bcache/util.h b/drivers/md/bcache/util.h
> index 1d04c48..cf2cbc2 100644
> --- a/drivers/md/bcache/util.h
> +++ b/drivers/md/bcache/util.h
> @@ -4,6 +4,7 @@
>  
>  #include <linux/blkdev.h>
>  #include <linux/errno.h>
> +#include <linux/blkdev.h>
>  #include <linux/kernel.h>
>  #include <linux/llist.h>
>  #include <linux/ratelimit.h>
> @@ -570,10 +571,10 @@ static inline sector_t bdev_sectors(struct block_device *bdev)
>  	return bdev->bd_inode->i_size >> 9;
>  }
>  
> -#define closure_bio_submit(bio, cl, dev)				\
> +#define closure_bio_submit(bio, cl)					\
>  do {									\
>  	closure_get(cl);						\
> -	bch_generic_make_request(bio, &(dev)->bio_split_hook);		\
> +	generic_make_request(bio);					\
>  } while (0)
>  
>  uint64_t bch_crc64_update(uint64_t, const void *, size_t);
> diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
> index f1986bc..ca38362 100644
> --- a/drivers/md/bcache/writeback.c
> +++ b/drivers/md/bcache/writeback.c
> @@ -188,7 +188,7 @@ static void write_dirty(struct closure *cl)
>  	io->bio.bi_bdev		= io->dc->bdev;
>  	io->bio.bi_end_io	= dirty_endio;
>  
> -	closure_bio_submit(&io->bio, cl, &io->dc->disk);
> +	closure_bio_submit(&io->bio, cl);
>  
>  	continue_at(cl, write_dirty_finish, system_wq);
>  }
> @@ -208,7 +208,7 @@ static void read_dirty_submit(struct closure *cl)
>  {
>  	struct dirty_io *io = container_of(cl, struct dirty_io, cl);
>  
> -	closure_bio_submit(&io->bio, cl, &io->dc->disk);
> +	closure_bio_submit(&io->bio, cl);
>  
>  	continue_at(cl, write_dirty, system_wq);
>  }
> -- 
> 2.1.4
> 
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