[PATCH 3/4] block: optionally merge discontiguous discard bios into a single request
Ming Lei
tom.leiming at gmail.com
Wed Feb 8 02:54:24 PST 2017
On Wed, Feb 8, 2017 at 12:46 AM, Christoph Hellwig <hch at lst.de> wrote:
> Add a new merge strategy that merges discard bios into a request until the
> maximum number of discard ranges (or the maximum discard size) is reached
> from the plug merging code. I/O scheduler merging is not wired up yet
> but might also be useful, although not for fast devices like NVMe which
> are the only user for now.
>
> Note that for now we don't support limiting the size of each discard range,
> but if needed that can be added later.
>
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
> block/blk-core.c | 27 +++++++++++++++++++++++++++
> block/blk-merge.c | 5 ++++-
> block/blk-mq.c | 3 +++
> block/blk-settings.c | 20 ++++++++++++++++++++
> block/blk-sysfs.c | 12 ++++++++++++
> block/blk.h | 2 ++
> include/linux/blkdev.h | 26 ++++++++++++++++++++++++++
> include/linux/elevator.h | 1 +
> 8 files changed, 95 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 75fe534861df..b9e857f4afe8 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1485,6 +1485,30 @@ bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
> return true;
> }
>
> +bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
> + struct bio *bio)
> +{
> + unsigned short segments = blk_rq_nr_discard_segments(req);
> +
> + if (segments >= queue_max_discard_segments(q))
> + goto no_merge;
> + if (blk_rq_sectors(req) + bio_sectors(bio) >
> + blk_rq_get_max_sectors(req, blk_rq_pos(req)))
> + goto no_merge;
> +
> + req->biotail->bi_next = bio;
> + req->biotail = bio;
> + req->__data_len += bio->bi_iter.bi_size;
typeof(__data_len) is unsigned, and should be easy to overflow
for discard rq's merge.
> + req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
> + req->nr_phys_segments = segments + 1;
> +
> + blk_account_io_start(req, false);
> + return true;
> +no_merge:
> + req_set_nomerge(q, req);
> + return false;
> +}
> +
> /**
> * blk_attempt_plug_merge - try to merge with %current's plugged list
> * @q: request_queue new bio is being queued at
> @@ -1549,6 +1573,9 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
> case ELEVATOR_FRONT_MERGE:
> merged = bio_attempt_front_merge(q, rq, bio);
> break;
> + case ELEVATOR_DISCARD_MERGE:
> + merged = bio_attempt_discard_merge(q, rq, bio);
> + break;
> default:
> break;
> }
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 6cbd90ad5f90..2afa262425d1 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -803,7 +803,10 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
>
> enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
> {
> - if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
> + if (req_op(rq) == REQ_OP_DISCARD &&
> + queue_max_discard_segments(rq->q) > 1)
> + return ELEVATOR_DISCARD_MERGE;
> + else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
> return ELEVATOR_BACK_MERGE;
> else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
> return ELEVATOR_FRONT_MERGE;
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 9294633759d9..89cb2d224488 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -780,6 +780,9 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
> if (blk_mq_sched_allow_merge(q, rq, bio))
> merged = bio_attempt_front_merge(q, rq, bio);
> break;
> + case ELEVATOR_DISCARD_MERGE:
> + merged = bio_attempt_discard_merge(q, rq, bio);
> + break;
> default:
> continue;
> }
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 6eb19bcbf3cb..9a68c8c19aaa 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -88,6 +88,7 @@ EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
> void blk_set_default_limits(struct queue_limits *lim)
> {
> lim->max_segments = BLK_MAX_SEGMENTS;
> + lim->max_discard_segments = 1;
> lim->max_integrity_segments = 0;
> lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
> lim->virt_boundary_mask = 0;
> @@ -128,6 +129,7 @@ void blk_set_stacking_limits(struct queue_limits *lim)
> /* Inherit limits from component devices */
> lim->discard_zeroes_data = 1;
> lim->max_segments = USHRT_MAX;
> + lim->max_discard_segments = 1;
> lim->max_hw_sectors = UINT_MAX;
> lim->max_segment_size = UINT_MAX;
> lim->max_sectors = UINT_MAX;
> @@ -337,6 +339,22 @@ void blk_queue_max_segments(struct request_queue *q, unsigned short max_segments
> EXPORT_SYMBOL(blk_queue_max_segments);
>
> /**
> + * blk_queue_max_discard_segments - set max segments for discard requests
> + * @q: the request queue for the device
> + * @max_segments: max number of segments
> + *
> + * Description:
> + * Enables a low level driver to set an upper limit on the number of
> + * segments in a discard request.
> + **/
> +void blk_queue_max_discard_segments(struct request_queue *q,
> + unsigned short max_segments)
> +{
> + q->limits.max_discard_segments = max_segments;
> +}
> +EXPORT_SYMBOL(blk_queue_max_discard_segments);
> +
> +/**
> * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
> * @q: the request queue for the device
> * @max_size: max size of segment in bytes
> @@ -553,6 +571,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
> b->virt_boundary_mask);
>
> t->max_segments = min_not_zero(t->max_segments, b->max_segments);
> + t->max_discard_segments = min_not_zero(t->max_discard_segments,
> + b->max_discard_segments);
> t->max_integrity_segments = min_not_zero(t->max_integrity_segments,
> b->max_integrity_segments);
>
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 48032c4759a7..070d81bae1d5 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -121,6 +121,12 @@ static ssize_t queue_max_segments_show(struct request_queue *q, char *page)
> return queue_var_show(queue_max_segments(q), (page));
> }
>
> +static ssize_t queue_max_discard_segments_show(struct request_queue *q,
> + char *page)
> +{
> + return queue_var_show(queue_max_discard_segments(q), (page));
> +}
> +
> static ssize_t queue_max_integrity_segments_show(struct request_queue *q, char *page)
> {
> return queue_var_show(q->limits.max_integrity_segments, (page));
> @@ -545,6 +551,11 @@ static struct queue_sysfs_entry queue_max_segments_entry = {
> .show = queue_max_segments_show,
> };
>
> +static struct queue_sysfs_entry queue_max_discard_segments_entry = {
> + .attr = {.name = "max_discard_segments", .mode = S_IRUGO },
> + .show = queue_max_discard_segments_show,
> +};
> +
> static struct queue_sysfs_entry queue_max_integrity_segments_entry = {
> .attr = {.name = "max_integrity_segments", .mode = S_IRUGO },
> .show = queue_max_integrity_segments_show,
> @@ -697,6 +708,7 @@ static struct attribute *default_attrs[] = {
> &queue_max_hw_sectors_entry.attr,
> &queue_max_sectors_entry.attr,
> &queue_max_segments_entry.attr,
> + &queue_max_discard_segments_entry.attr,
> &queue_max_integrity_segments_entry.attr,
> &queue_max_segment_size_entry.attr,
> &queue_iosched_entry.attr,
> diff --git a/block/blk.h b/block/blk.h
> index ae82f2ac4019..d1ea4bd9b9a3 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -100,6 +100,8 @@ bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
> struct bio *bio);
> bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
> struct bio *bio);
> +bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
> + struct bio *bio);
> bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
> unsigned int *request_count,
> struct request **same_queue_rq);
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index e0bac14347e6..aecca0e7d9ca 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -331,6 +331,7 @@ struct queue_limits {
> unsigned short logical_block_size;
> unsigned short max_segments;
> unsigned short max_integrity_segments;
> + unsigned short max_discard_segments;
>
> unsigned char misaligned;
> unsigned char discard_misaligned;
> @@ -1146,6 +1147,8 @@ extern void blk_queue_bounce_limit(struct request_queue *, u64);
> extern void blk_queue_max_hw_sectors(struct request_queue *, unsigned int);
> extern void blk_queue_chunk_sectors(struct request_queue *, unsigned int);
> extern void blk_queue_max_segments(struct request_queue *, unsigned short);
> +extern void blk_queue_max_discard_segments(struct request_queue *,
> + unsigned short);
> extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
> extern void blk_queue_max_discard_sectors(struct request_queue *q,
> unsigned int max_discard_sectors);
> @@ -1189,6 +1192,15 @@ extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
> extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable);
> extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fua);
>
> +/*
> + * Number of physical segments as sent to the device.
> + *
> + * Normally this is the number of discontiguous data segments sent by the
> + * submitter. But for data-less command like discard we might have no
> + * actual data segments submitted, but the driver might have to add it's
> + * own special payload. In that case we still return 1 here so that this
> + * special payload will be mapped.
> + */
> static inline unsigned short blk_rq_nr_phys_segments(struct request *rq)
> {
> if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
> @@ -1196,6 +1208,15 @@ static inline unsigned short blk_rq_nr_phys_segments(struct request *rq)
> return rq->nr_phys_segments;
> }
>
> +/*
> + * Number of discard segments (or ranges) the driver needs to fill in.
> + * Each discard bio merged into a request is counted as one segment.
> + */
> +static inline unsigned short blk_rq_nr_discard_segments(struct request *rq)
> +{
> + return max_t(unsigned short, rq->nr_phys_segments, 1);
> +}
> +
> extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
> extern void blk_dump_rq_flags(struct request *, char *);
> extern long nr_blockdev_pages(void);
> @@ -1384,6 +1405,11 @@ static inline unsigned short queue_max_segments(struct request_queue *q)
> return q->limits.max_segments;
> }
>
> +static inline unsigned short queue_max_discard_segments(struct request_queue *q)
> +{
> + return q->limits.max_discard_segments;
> +}
> +
> static inline unsigned int queue_max_segment_size(struct request_queue *q)
> {
> return q->limits.max_segment_size;
> diff --git a/include/linux/elevator.h b/include/linux/elevator.h
> index b38b4e651ea6..8265b6330cc2 100644
> --- a/include/linux/elevator.h
> +++ b/include/linux/elevator.h
> @@ -16,6 +16,7 @@ enum elv_merge {
> ELEVATOR_NO_MERGE = 0,
> ELEVATOR_FRONT_MERGE = 1,
> ELEVATOR_BACK_MERGE = 2,
> + ELEVATOR_DISCARD_MERGE = 3,
> };
>
> typedef enum elv_merge (elevator_merge_fn) (struct request_queue *, struct request **,
> --
> 2.11.0
>
--
Ming Lei
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