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[PATCH 02/11] blk: make the bioset rescue_workqueue optional.

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  [PATCH 02/11] blk: make the bioset rescue_workqueue optional. NeilBrown <neilb@suse.com> - 2017-04-20 07:50 +0200
    Re: [PATCH 02/11] blk: make the bioset rescue_workqueue optional. Christoph Hellwig <hch@infradead.org> - 2017-04-21 13:30 +0200
      Re: [PATCH 02/11] blk: make the bioset rescue_workqueue optional. NeilBrown <neilb@suse.com> - 2017-04-24 04:00 +0200
        Re: [PATCH 02/11] blk: make the bioset rescue_workqueue optional. Christoph Hellwig <hch@infradead.org> - 2017-04-24 17:20 +0200

#1627003 — [PATCH 02/11] blk: make the bioset rescue_workqueue optional.

This patch converts bioset_create() and
bioset_create_nobvec() to not create a workqueue so
alloctions will never trigger punt_bios_to_rescuer().  It
also introduces bioset_create_rescued() and
bioset_create_nobvec_rescued() which preserve the old
behaviour.

All callers of bioset_create() and bioset_create_nobvec(),
that are inside block device drivers, are converted to the
_rescued() version.

biosets used by filesystems or other top-level users do not
need rescuing as the bio can never be queued behind other
bios.  This includes fs_bio_set, blkdev_dio_pool,
btrfs_bioset, xfs_ioend_bioset, drbd_md_io_bio_set,
and one allocated by target_core_iblock.c.

biosets used by md/raid to not need rescuing as
their usage was recently audited to revised to never
risk deadlock.

It is hoped that most, if not all, of the remaining biosets
can end up being the non-rescued version.

Signed-off-by: NeilBrown <neilb@suse.com>
---
 block/bio.c               |   28 ++++++++++++++++++++++++----
 block/blk-core.c          |    2 +-
 drivers/md/bcache/super.c |    4 ++--
 drivers/md/dm-crypt.c     |    2 +-
 drivers/md/dm-io.c        |    2 +-
 drivers/md/dm.c           |    5 +++--
 include/linux/bio.h       |    2 ++
 7 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 888e7801c638..b8e304015dc8 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -363,6 +363,8 @@ static void punt_bios_to_rescuer(struct bio_set *bs)
 	struct bio_list punt, nopunt;
 	struct bio *bio;
 
+	if (!WARN_ON_ONCE(!bs->rescue_workqueue))
+		return;
 	/*
 	 * In order to guarantee forward progress we must punt only bios that
 	 * were allocated from this bio_set; otherwise, if there was a bio on
@@ -474,7 +476,8 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, unsigned int nr_iovecs,
 
 		if (current->bio_list &&
 		    (!bio_list_empty(&current->bio_list[0]) ||
-		     !bio_list_empty(&current->bio_list[1])))
+		     !bio_list_empty(&current->bio_list[1])) &&
+		    bs->rescue_workqueue)
 			gfp_mask &= ~__GFP_DIRECT_RECLAIM;
 
 		p = mempool_alloc(bs->bio_pool, gfp_mask);
@@ -1923,7 +1926,8 @@ EXPORT_SYMBOL(bioset_free);
 
 static struct bio_set *__bioset_create(unsigned int pool_size,
 				       unsigned int front_pad,
-				       bool create_bvec_pool)
+				       bool create_bvec_pool,
+				       bool create_rescue_workqueue)
 {
 	unsigned int back_pad = BIO_INLINE_VECS * sizeof(struct bio_vec);
 	struct bio_set *bs;
@@ -1954,6 +1958,9 @@ static struct bio_set *__bioset_create(unsigned int pool_size,
 			goto bad;
 	}
 
+	if (!create_rescue_workqueue)
+		return bs;
+
 	bs->rescue_workqueue = alloc_workqueue("bioset", WQ_MEM_RECLAIM, 0);
 	if (!bs->rescue_workqueue)
 		goto bad;
@@ -1979,10 +1986,16 @@ static struct bio_set *__bioset_create(unsigned int pool_size,
  */
 struct bio_set *bioset_create(unsigned int pool_size, unsigned int front_pad)
 {
-	return __bioset_create(pool_size, front_pad, true);
+	return __bioset_create(pool_size, front_pad, true, false);
 }
 EXPORT_SYMBOL(bioset_create);
 
+struct bio_set *bioset_create_rescued(unsigned int pool_size, unsigned int front_pad)
+{
+	return __bioset_create(pool_size, front_pad, true, true);
+}
+EXPORT_SYMBOL(bioset_create_rescued);
+
 /**
  * bioset_create_nobvec  - Create a bio_set without bio_vec mempool
  * @pool_size:	Number of bio to cache in the mempool
@@ -1994,10 +2007,17 @@ EXPORT_SYMBOL(bioset_create);
  */
 struct bio_set *bioset_create_nobvec(unsigned int pool_size, unsigned int front_pad)
 {
-	return __bioset_create(pool_size, front_pad, false);
+	return __bioset_create(pool_size, front_pad, false, false);
 }
 EXPORT_SYMBOL(bioset_create_nobvec);
 
+struct bio_set *bioset_create_nobvec_rescued(unsigned int pool_size,
+					     unsigned int front_pad)
+{
+	return __bioset_create(pool_size, front_pad, false, true);
+}
+EXPORT_SYMBOL(bioset_create_nobvec_rescued);
+
 #ifdef CONFIG_BLK_CGROUP
 
 /**
diff --git a/block/blk-core.c b/block/blk-core.c
index f5d64ad75b36..23f20cb84b2f 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -728,7 +728,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 	if (q->id < 0)
 		goto fail_q;
 
-	q->bio_split = bioset_create(BIO_POOL_SIZE, 0);
+	q->bio_split = bioset_create_rescued(BIO_POOL_SIZE, 0);
 	if (!q->bio_split)
 		goto fail_id;
 
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 85e3f21c2514..6cb30792f0ed 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -786,7 +786,7 @@ static int bcache_device_init(struct bcache_device *d, unsigned block_size,
 
 	minor *= BCACHE_MINORS;
 
-	if (!(d->bio_split = bioset_create(4, offsetof(struct bbio, bio))) ||
+	if (!(d->bio_split = bioset_create_rescued(4, offsetof(struct bbio, bio))) ||
 	    !(d->disk = alloc_disk(BCACHE_MINORS))) {
 		ida_simple_remove(&bcache_minor, minor);
 		return -ENOMEM;
@@ -1520,7 +1520,7 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
 				sizeof(struct bbio) + sizeof(struct bio_vec) *
 				bucket_pages(c))) ||
 	    !(c->fill_iter = mempool_create_kmalloc_pool(1, iter_size)) ||
-	    !(c->bio_split = bioset_create(4, offsetof(struct bbio, bio))) ||
+	    !(c->bio_split = bioset_create_rescued(4, offsetof(struct bbio, bio))) ||
 	    !(c->uuids = alloc_bucket_pages(GFP_KERNEL, c)) ||
 	    !(c->moving_gc_wq = alloc_workqueue("bcache_gc",
 						WQ_MEM_RECLAIM, 0)) ||
diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index ef1d836bd81b..b7b1df84fe4a 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -1936,7 +1936,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		goto bad;
 	}
 
-	cc->bs = bioset_create(MIN_IOS, 0);
+	cc->bs = bioset_create_rescued(MIN_IOS, 0);
 	if (!cc->bs) {
 		ti->error = "Cannot allocate crypt bioset";
 		goto bad;
diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 3702e502466d..5557d5d97b5b 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -58,7 +58,7 @@ struct dm_io_client *dm_io_client_create(void)
 	if (!client->pool)
 		goto bad;
 
-	client->bios = bioset_create(min_ios, 0);
+	client->bios = bioset_create_rescued(min_ios, 0);
 	if (!client->bios)
 		goto bad;
 
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 8bf397729bbd..5590c571c0e7 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1014,7 +1014,8 @@ static void flush_current_bio_list(struct blk_plug_cb *cb, bool from_schedule)
 
 		while ((bio = bio_list_pop(&list))) {
 			struct bio_set *bs = bio->bi_pool;
-			if (unlikely(!bs) || bs == fs_bio_set) {
+			if (unlikely(!bs) || bs == fs_bio_set ||
+			    !bs->rescue_workqueue) {
 				bio_list_add(&current->bio_list[i], bio);
 				continue;
 			}
@@ -2601,7 +2602,7 @@ struct dm_md_mempools *dm_alloc_md_mempools(struct mapped_device *md, unsigned t
 		BUG();
 	}
 
-	pools->bs = bioset_create_nobvec(pool_size, front_pad);
+	pools->bs = bioset_create_nobvec_rescued(pool_size, front_pad);
 	if (!pools->bs)
 		goto out;
 
diff --git a/include/linux/bio.h b/include/linux/bio.h
index d1b04b0e99cf..2eb8bfae5276 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -374,7 +374,9 @@ static inline struct bio *bio_next_split(struct bio *bio, int sectors,
 }
 
 extern struct bio_set *bioset_create(unsigned int, unsigned int);
+extern struct bio_set *bioset_create_rescued(unsigned int, unsigned int);
 extern struct bio_set *bioset_create_nobvec(unsigned int, unsigned int);
+extern struct bio_set *bioset_create_nobvec_rescued(unsigned int, unsigned int);
 extern void bioset_free(struct bio_set *);
 extern mempool_t *biovec_create_pool(int pool_entries);
 

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#1628151

On Thu, Apr 20, 2017 at 03:38:48PM +1000, NeilBrown wrote:
> This patch converts bioset_create() and
> bioset_create_nobvec() to not create a workqueue so
> alloctions will never trigger punt_bios_to_rescuer().  It
> also introduces bioset_create_rescued() and
> bioset_create_nobvec_rescued() which preserve the old
> behaviour.

Why these super-early line breaks in the committ message?  They make
the text much more awkware compared to say:

This patch converts bioset_create() and bioset_create_nobvec() to not
create a workqueue so alloctions will never trigger
punt_bios_to_rescuer(). It also introduces bioset_create_rescued() and
bioset_create_nobvec_rescued() which preserve the old behaviour.

>  static struct bio_set *__bioset_create(unsigned int pool_size,
>  				       unsigned int front_pad,
> -				       bool create_bvec_pool)
> +				       bool create_bvec_pool,
> +				       bool create_rescue_workqueue)

I'd much prefer a single new bioset_create with a bunch of flags
arguments over the number of new functions and these bool arguments.

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#1629123

[Multipart message — attachments visible in raw view] — view raw

On Fri, Apr 21 2017, Christoph Hellwig wrote:

> On Thu, Apr 20, 2017 at 03:38:48PM +1000, NeilBrown wrote:
>> This patch converts bioset_create() and
>> bioset_create_nobvec() to not create a workqueue so
>> alloctions will never trigger punt_bios_to_rescuer().  It
>> also introduces bioset_create_rescued() and
>> bioset_create_nobvec_rescued() which preserve the old
>> behaviour.
>
> Why these super-early line breaks in the committ message?  They make
> the text much more awkware compared to say:

I usually set a smaller wrap-margin for git comments because of the
extra space that git inserts on the left.  Maybe I over-do it.

>
> This patch converts bioset_create() and bioset_create_nobvec() to not
> create a workqueue so alloctions will never trigger
> punt_bios_to_rescuer(). It also introduces bioset_create_rescued() and
> bioset_create_nobvec_rescued() which preserve the old behaviour.
>
>>  static struct bio_set *__bioset_create(unsigned int pool_size,
>>  				       unsigned int front_pad,
>> -				       bool create_bvec_pool)
>> +				       bool create_bvec_pool,
>> +				       bool create_rescue_workqueue)
>
> I'd much prefer a single new bioset_create with a bunch of flags
> arguments over the number of new functions and these bool arguments.

I was following the existing practice exemplified by
bioset_create_nobvec().
By not changing the signature of the function, I can avoid touching
quite a few places where it is called.
I hope to get rid of the _rescued() versions eventually.  That is easier
if there are a separate function rather than an extra arg that needs
to be removed everywhere.

NeilBrown

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#1629663

On Mon, Apr 24, 2017 at 11:51:01AM +1000, NeilBrown wrote:
> 
> I was following the existing practice exemplified by
> bioset_create_nobvec().

Which is pretty ugly to start with..

> By not changing the signature of the function, I can avoid touching
> quite a few places where it is called.

There are 13 callers of bioset_create and one caller of
bioset_create_nobvec, and your series touches many of those.

So just adding a flags argument to bioset_create and passing
BIOSET_NEED_BVECS and BIOSET_NEED_RESUER flags to it doesn't seem
to much of an effort, and it's going to create a much nicer and easier
to extend interface.

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