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

Bob Liu
2020-01-19T01:51:30Z

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)
>
>