Re: [PATCH 03/13] blk: make the bioset rescue_workqueue optional.

Christoph Hellwig
2017-05-02T08:14:25Z

On Tue, May 02, 2017 at 01:42:24PM +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.
>
> 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 | 12 ++++++++++--
> block/blk-core.c | 2 +-
> drivers/md/bcache/super.c | 6 ++++--
> drivers/md/dm-crypt.c | 2 +-
> drivers/md/dm-io.c | 2 +-
> drivers/md/dm.c | 5 +++--
> include/linux/bio.h | 1 +
> 7 files changed, 21 insertions(+), 9 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 3f1286ed301e..257606e742e0 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);
> @@ -1925,7 +1928,7 @@ EXPORT_SYMBOL(bioset_free);
> * bioset_create - Create a bio_set
> * @pool_size: Number of bio and bio_vecs to cache in the mempool
> * @front_pad: Number of bytes to allocate in front of the returned bio
> - * @flags: Flags to modify behavior, currently only %BIOSET_NEED_BVECS
> + * @flags: Flags to modify behavior, currently %BIOSET_NEED_BVECS and %BIOSET_NEED_RESCUER
> *
> * Description:
> * Set up a bio_set to be used with @bio_alloc_bioset. Allows the caller
> @@ -1936,6 +1939,8 @@ EXPORT_SYMBOL(bioset_free);
> * or things will break badly.
> * If %BIOSET_NEED_BVECS is set in @flags, a separate pool will be allocated
> * for allocating iovecs. This pool is not needed e.g. for bio_clone_fast().
> + * If %BIOSET_NEED_RESCUER is set, workqueue is create which can be used to
> + * dispatch queued requests when the mempool runs out of space.
> *
> */
> struct bio_set *bioset_create(unsigned int pool_size,
> @@ -1971,6 +1976,9 @@ struct bio_set *bioset_create(unsigned int pool_size,
> goto bad;
> }
>
> + if (!(flags & BIOSET_NEED_RESCUER))
> + return bs;
> +
> bs->rescue_workqueue = alloc_workqueue("bioset", WQ_MEM_RECLAIM, 0);
> if (!bs->rescue_workqueue)
> goto bad;
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 3797753f4085..ae51f159a2ca 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -730,7 +730,7 @@ 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, BIOSET_NEED_BVECS);
> + q->bio_split = bioset_create(BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS | BIOSET_NEED_RESCUER);

Please avoid > 80 char lines.

Otherwise looks fine,

Reviewed-by: Christoph Hellwig <hch@lst.de>