Re: [PATCH block v2 2/3] block: Add support for REQ_NOZERO flag

[Bob Liu <bob.liu@oracle.com>]

On 1/16/20 8:36 PM, Kirill Tkhai wrote:
> This adds support for REQ_NOZERO extension of REQ_OP_WRITE_ZEROES
> operation, which encourages a block device driver to just allocate
> blocks (or mark them allocated) instead of actual blocks zeroing.
> REQ_NOZERO is aimed to be used for network filesystems providing
> a block device interface. Also, block devices, which map a file
> on other filesystem (like loop), may use this for less fragmentation
> and batching fallocate() requests. Hypervisors like QEMU may
> introduce optimizations of clusters allocations based on this.
> 
> BLKDEV_ZERO_ALLOCATE is a new corresponding flag for
> blkdev_issue_zeroout().
>> CC: Martin K. Petersen <martin.petersen@oracle.com>
> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> ---
>  block/blk-core.c          |    6 +++---
>  block/blk-lib.c           |   17 ++++++++++-------
>  block/blk-merge.c         |    9 ++++++---
>  block/blk-settings.c      |   17 +++++++++++++++++
>  fs/block_dev.c            |    4 ++++
>  include/linux/blk_types.h |    5 ++++-
>  include/linux/blkdev.h    |   31 ++++++++++++++++++++++++-------
>  7 files changed, 68 insertions(+), 21 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 50a5de025d5e..2edcd55624f1 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -978,7 +978,7 @@ generic_make_request_checks(struct bio *bio)
>  			goto not_supported;
>  		break;
>  	case REQ_OP_WRITE_ZEROES:
> -		if (!q->limits.max_write_zeroes_sectors)
> +		if (!blk_queue_get_max_write_zeroes_sectors(q, bio->bi_opf))
>  			goto not_supported;
>  		break;
>  	default:
> @@ -1250,10 +1250,10 @@ EXPORT_SYMBOL(submit_bio);
>  static int blk_cloned_rq_check_limits(struct request_queue *q,
>  				      struct request *rq)
>  {
> -	if (blk_rq_sectors(rq) > blk_queue_get_max_sectors(q, req_op(rq))) {
> +	if (blk_rq_sectors(rq) > blk_queue_get_max_sectors(q, rq->cmd_flags)) {
>  		printk(KERN_ERR "%s: over max size limit. (%u > %u)\n",
>  			__func__, blk_rq_sectors(rq),
> -			blk_queue_get_max_sectors(q, req_op(rq)));
> +			blk_queue_get_max_sectors(q, rq->cmd_flags));
>  		return -EIO;
>  	}
>  
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 3e38c93cfc53..3e80279eb029 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -214,7 +214,7 @@ static int __blkdev_issue_write_zeroes(struct block_device *bdev,
>  		struct bio **biop, unsigned flags)
>  {
>  	struct bio *bio = *biop;
> -	unsigned int max_write_zeroes_sectors;
> +	unsigned int max_write_zeroes_sectors, req_flags = 0;
>  	struct request_queue *q = bdev_get_queue(bdev);
>  
>  	if (!q)
> @@ -224,18 +224,21 @@ static int __blkdev_issue_write_zeroes(struct block_device *bdev,
>  		return -EPERM;
>  
>  	/* Ensure that max_write_zeroes_sectors doesn't overflow bi_size */
> -	max_write_zeroes_sectors = bdev_write_zeroes_sectors(bdev, 0);
> +	max_write_zeroes_sectors = bdev_write_zeroes_sectors(bdev, flags);
>  
>  	if (max_write_zeroes_sectors == 0)
>  		return -EOPNOTSUPP;
>  
> +	if (flags & BLKDEV_ZERO_NOUNMAP)
> +		req_flags |= REQ_NOUNMAP;
> +	if (flags & BLKDEV_ZERO_ALLOCATE)
> +		req_flags |= REQ_NOZERO|REQ_NOUNMAP;
> +
>  	while (nr_sects) {
>  		bio = blk_next_bio(bio, 0, gfp_mask);
>  		bio->bi_iter.bi_sector = sector;
>  		bio_set_dev(bio, bdev);
> -		bio->bi_opf = REQ_OP_WRITE_ZEROES;
> -		if (flags & BLKDEV_ZERO_NOUNMAP)
> -			bio->bi_opf |= REQ_NOUNMAP;
> +		bio->bi_opf = REQ_OP_WRITE_ZEROES | req_flags;
>  
>  		if (nr_sects > max_write_zeroes_sectors) {
>  			bio->bi_iter.bi_size = max_write_zeroes_sectors << 9;
> @@ -362,7 +365,7 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
>  	sector_t bs_mask;
>  	struct bio *bio;
>  	struct blk_plug plug;
> -	bool try_write_zeroes = !!bdev_write_zeroes_sectors(bdev, 0);
> +	bool try_write_zeroes = !!bdev_write_zeroes_sectors(bdev, flags);
>  
>  	bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
>  	if ((sector | nr_sects) & bs_mask)
> @@ -391,7 +394,7 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
>  			try_write_zeroes = false;
>  			goto retry;
>  		}
> -		if (!bdev_write_zeroes_sectors(bdev, 0)) {
> +		if (!bdev_write_zeroes_sectors(bdev, flags)) {
>  			/*
>  			 * Zeroing offload support was indicated, but the
>  			 * device reported ILLEGAL REQUEST (for some devices
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 347782a24a35..e3ce4b87bbaa 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -105,15 +105,18 @@ static struct bio *blk_bio_discard_split(struct request_queue *q,
>  static struct bio *blk_bio_write_zeroes_split(struct request_queue *q,
>  		struct bio *bio, struct bio_set *bs, unsigned *nsegs)
>  {
> +	unsigned int max_sectors;
> +
> +	max_sectors = blk_queue_get_max_write_zeroes_sectors(q, bio->bi_opf);
>  	*nsegs = 0;
>  
> -	if (!q->limits.max_write_zeroes_sectors)
> +	if (!max_sectors)
>  		return NULL;
>  
> -	if (bio_sectors(bio) <= q->limits.max_write_zeroes_sectors)
> +	if (bio_sectors(bio) <= max_sectors)
>  		return NULL;
>  
> -	return bio_split(bio, q->limits.max_write_zeroes_sectors, GFP_NOIO, bs);
> +	return bio_split(bio, max_sectors, GFP_NOIO, bs);
>  }
>  
>  static struct bio *blk_bio_write_same_split(struct request_queue *q,
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 5f6dcc7a47bd..f682374c5106 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -48,6 +48,7 @@ void blk_set_default_limits(struct queue_limits *lim)
>  	lim->chunk_sectors = 0;
>  	lim->max_write_same_sectors = 0;
>  	lim->max_write_zeroes_sectors = 0;
> +	lim->max_allocate_sectors = 0;
>  	lim->max_discard_sectors = 0;
>  	lim->max_hw_discard_sectors = 0;
>  	lim->discard_granularity = 0;
> @@ -83,6 +84,7 @@ void blk_set_stacking_limits(struct queue_limits *lim)
>  	lim->max_dev_sectors = UINT_MAX;
>  	lim->max_write_same_sectors = UINT_MAX;
>  	lim->max_write_zeroes_sectors = UINT_MAX;
> +	lim->max_allocate_sectors = UINT_MAX;
>  }
>  EXPORT_SYMBOL(blk_set_stacking_limits);
>  
> @@ -257,6 +259,19 @@ void blk_queue_max_write_zeroes_sectors(struct request_queue *q,
>  }
>  EXPORT_SYMBOL(blk_queue_max_write_zeroes_sectors);
>  
> +/**
> + * blk_queue_max_allocate_sectors - set max sectors for a single
> + *                                  allocate request
> + * @q:  the request queue for the device
> + * @max_allocate_sectors: maximum number of sectors to write per command
> + **/
> +void blk_queue_max_allocate_sectors(struct request_queue *q,
> +		unsigned int max_allocate_sectors)
> +{
> +	q->limits.max_allocate_sectors = max_allocate_sectors;
> +}
> +EXPORT_SYMBOL(blk_queue_max_allocate_sectors);
> +

I'd suggest split this to a separated patch.

>  /**
>   * blk_queue_max_segments - set max hw segments for a request for this queue
>   * @q:  the request queue for the device
> @@ -506,6 +521,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
>  					b->max_write_same_sectors);
>  	t->max_write_zeroes_sectors = min(t->max_write_zeroes_sectors,
>  					b->max_write_zeroes_sectors);
> +	t->max_allocate_sectors = min(t->max_allocate_sectors,
> +					b->max_allocate_sectors);
>  	t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
>  
>  	t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask,
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 69bf2fb6f7cd..1ffef894b3bd 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -2122,6 +2122,10 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
>  		error = blkdev_issue_zeroout(bdev, start >> 9, len >> 9,
>  					     GFP_KERNEL, BLKDEV_ZERO_NOFALLBACK);
>  		break;
> +	case FALLOC_FL_KEEP_SIZE:
> +		error = blkdev_issue_zeroout(bdev, start >> 9, len >> 9,
> +			GFP_KERNEL, BLKDEV_ZERO_ALLOCATE | BLKDEV_ZERO_NOFALLBACK);
> +		break;
>  	case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE | FALLOC_FL_NO_HIDE_STALE:
>  		error = blkdev_issue_discard(bdev, start >> 9, len >> 9,
>  					     GFP_KERNEL, 0);
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 70254ae11769..9ed166860099 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -335,7 +335,9 @@ enum req_flag_bits {
>  
>  	/* command specific flags for REQ_OP_WRITE_ZEROES: */
>  	__REQ_NOUNMAP,		/* do not free blocks when zeroing */
> -
> +	__REQ_NOZERO,		/* only notify about allocated blocks,
> +				 * and do not actual zero them
> +				 */
>  	__REQ_HIPRI,
>  
>  	/* for driver use */
> @@ -362,6 +364,7 @@ enum req_flag_bits {
>  #define REQ_CGROUP_PUNT		(1ULL << __REQ_CGROUP_PUNT)
>  
>  #define REQ_NOUNMAP		(1ULL << __REQ_NOUNMAP)
> +#define REQ_NOZERO		(1ULL << __REQ_NOZERO)
>  #define REQ_HIPRI		(1ULL << __REQ_HIPRI)
>  
>  #define REQ_DRV			(1ULL << __REQ_DRV)
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 4cd69552df9a..f4ec5db64432 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -336,6 +336,7 @@ struct queue_limits {
>  	unsigned int		max_hw_discard_sectors;
>  	unsigned int		max_write_same_sectors;
>  	unsigned int		max_write_zeroes_sectors;
> +	unsigned int		max_allocate_sectors;
>  	unsigned int		discard_granularity;
>  	unsigned int		discard_alignment;
>  
> @@ -988,9 +989,19 @@ static inline struct bio_vec req_bvec(struct request *rq)
>  	return mp_bvec_iter_bvec(rq->bio->bi_io_vec, rq->bio->bi_iter);
>  }
>  
> +static inline unsigned int blk_queue_get_max_write_zeroes_sectors(
> +		struct request_queue *q, unsigned int op_flags)
> +{
> +	if (op_flags & REQ_NOZERO)
> +		return q->limits.max_allocate_sectors;
> +	return q->limits.max_write_zeroes_sectors;
> +}
> +

And this one.
Also, should we consider other code path used q->limits.max_write_zeroes_sectors?

Regards,
Bob

>  static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q,
> -						     int op)
> +						     unsigned int op_flags)
>  {
> +	int op = op_flags & REQ_OP_MASK;
> +
>  	if (unlikely(op == REQ_OP_DISCARD || op == REQ_OP_SECURE_ERASE))
>  		return min(q->limits.max_discard_sectors,
>  			   UINT_MAX >> SECTOR_SHIFT);
> @@ -999,7 +1010,7 @@ static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q,
>  		return q->limits.max_write_same_sectors;
>  
>  	if (unlikely(op == REQ_OP_WRITE_ZEROES))
> -		return q->limits.max_write_zeroes_sectors;
> +		return blk_queue_get_max_write_zeroes_sectors(q, op_flags);
>  
>  	return q->limits.max_sectors;
>  }
> @@ -1029,10 +1040,10 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
>  	if (!q->limits.chunk_sectors ||
>  	    req_op(rq) == REQ_OP_DISCARD ||
>  	    req_op(rq) == REQ_OP_SECURE_ERASE)
> -		return blk_queue_get_max_sectors(q, req_op(rq));
> +		return blk_queue_get_max_sectors(q, rq->cmd_flags);
>  
>  	return min(blk_max_size_offset(q, offset),
> -			blk_queue_get_max_sectors(q, req_op(rq)));
> +			blk_queue_get_max_sectors(q, rq->cmd_flags));
>  }
>  
>  static inline unsigned int blk_rq_count_bios(struct request *rq)
> @@ -1078,6 +1089,8 @@ extern void blk_queue_max_write_same_sectors(struct request_queue *q,
>  		unsigned int max_write_same_sectors);
>  extern void blk_queue_max_write_zeroes_sectors(struct request_queue *q,
>  		unsigned int max_write_same_sectors);
> +extern void blk_queue_max_allocate_sectors(struct request_queue *q,
> +		unsigned int max_allocate_sectors);
>  extern void blk_queue_logical_block_size(struct request_queue *, unsigned short);
>  extern void blk_queue_physical_block_size(struct request_queue *, unsigned int);
>  extern void blk_queue_alignment_offset(struct request_queue *q,
> @@ -1219,6 +1232,7 @@ extern int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>  
>  #define BLKDEV_ZERO_NOUNMAP	(1 << 0)  /* do not free blocks */
>  #define BLKDEV_ZERO_NOFALLBACK	(1 << 1)  /* don't write explicit zeroes */
> +#define BLKDEV_ZERO_ALLOCATE	(1 << 2)  /* allocate range of blocks */
>  
>  extern int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
>  		sector_t nr_sects, gfp_t gfp_mask, struct bio **biop,
> @@ -1423,10 +1437,13 @@ static inline unsigned int bdev_write_zeroes_sectors(struct block_device *bdev,
>  {
>  	struct request_queue *q = bdev_get_queue(bdev);
>  
> -	if (q)
> -		return q->limits.max_write_zeroes_sectors;
> +	if (!q)
> +		return 0;
>  
> -	return 0;
> +	if (flags & BLKDEV_ZERO_ALLOCATE)
> +		return q->limits.max_allocate_sectors;
> +	else
> +		return q->limits.max_write_zeroes_sectors;
>  }
>  
>  static inline enum blk_zoned_model bdev_zoned_model(struct block_device *bdev)
> 
>