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Add 'discard' request handling

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Some block devices benefit from a hint that they can forget the contents
of certain sectors. Add basic support for this to the block core, along
with a 'blkdev_issue_discard()' helper function which issues such
requests.

The caller doesn't get to provide an end_io functio, since
blkdev_issue_discard() will automatically split the request up into
multiple bios if appropriate. Neither does the function wait for
completion -- it's expected that callers won't care about when, or even
_if_, the request completes. It's only a hint to the device anyway. By
definition, the file system doesn't _care_ about these sectors any more.

[With feedback from OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> and
Jens Axboe <jens.axboe@oracle.com]

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
David Woodhouse 2008-08-05 18:01:53 +01:00 • committed by Jens Axboe
commit fb2dce862d
6 changed files with 130 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

8
include/linux/bio.h
View file

@ -149,6 +149,8 @@ struct bio {
* bit 2 -- barrier
* bit 3 -- fail fast, don't want low level driver retries
* bit 4 -- synchronous I/O hint: the block layer will unplug immediately
* bit 5 -- metadata request
* bit 6 -- discard sectors
*/
#define BIO_RW 0 /* Must match RW in req flags (blkdev.h) */
#define BIO_RW_AHEAD 1 /* Must match FAILFAST in req flags */
@ -156,6 +158,7 @@ struct bio {
#define BIO_RW_FAILFAST 3
#define BIO_RW_SYNC 4
#define BIO_RW_META 5
#define BIO_RW_DISCARD 6
/*
* upper 16 bits of bi_rw define the io priority of this bio
@ -186,13 +189,14 @@ struct bio {
#define bio_rw_ahead(bio) ((bio)->bi_rw & (1 << BIO_RW_AHEAD))
#define bio_rw_meta(bio) ((bio)->bi_rw & (1 << BIO_RW_META))
#define bio_empty_barrier(bio) (bio_barrier(bio) && !bio_has_data(bio))
#define bio_discard(bio) ((bio)->bi_rw & (1 << BIO_RW_DISCARD))
static inline unsigned int bio_cur_sectors(struct bio *bio)
{
if (bio->bi_vcnt)
return bio_iovec(bio)->bv_len >> 9;
return 0;
else /* dataless requests such as discard */
return bio->bi_size >> 9;
}
static inline void *bio_data(struct bio *bio)

16
include/linux/blkdev.h
View file

@ -89,6 +89,7 @@ enum {
enum rq_flag_bits {
__REQ_RW, /* not set, read. set, write */
__REQ_FAILFAST, /* no low level driver retries */
__REQ_DISCARD, /* request to discard sectors */
__REQ_SORTED, /* elevator knows about this request */
__REQ_SOFTBARRIER, /* may not be passed by ioscheduler */
__REQ_HARDBARRIER, /* may not be passed by drive either */
@ -111,6 +112,7 @@ enum rq_flag_bits {
};
#define REQ_RW (1 << __REQ_RW)
#define REQ_DISCARD (1 << __REQ_DISCARD)
#define REQ_FAILFAST (1 << __REQ_FAILFAST)
#define REQ_SORTED (1 << __REQ_SORTED)
#define REQ_SOFTBARRIER (1 << __REQ_SOFTBARRIER)
@ -252,6 +254,7 @@ typedef void (request_fn_proc) (struct request_queue *q);
typedef int (make_request_fn) (struct request_queue *q, struct bio *bio);
typedef int (prep_rq_fn) (struct request_queue *, struct request *);
typedef void (unplug_fn) (struct request_queue *);
typedef int (prepare_discard_fn) (struct request_queue *, struct request *);
struct bio_vec;
struct bvec_merge_data {
@ -307,6 +310,7 @@ struct request_queue
make_request_fn *make_request_fn;
prep_rq_fn *prep_rq_fn;
unplug_fn *unplug_fn;
prepare_discard_fn *prepare_discard_fn;
merge_bvec_fn *merge_bvec_fn;
prepare_flush_fn *prepare_flush_fn;
softirq_done_fn *softirq_done_fn;
@ -546,6 +550,7 @@ enum {
#define blk_sorted_rq(rq) ((rq)->cmd_flags & REQ_SORTED)
#define blk_barrier_rq(rq) ((rq)->cmd_flags & REQ_HARDBARRIER)
#define blk_fua_rq(rq) ((rq)->cmd_flags & REQ_FUA)
#define blk_discard_rq(rq) ((rq)->cmd_flags & REQ_DISCARD)
#define blk_bidi_rq(rq) ((rq)->next_rq != NULL)
#define blk_empty_barrier(rq) (blk_barrier_rq(rq) && blk_fs_request(rq) && !(rq)->hard_nr_sectors)
/* rq->queuelist of dequeued request must be list_empty() */
@ -796,6 +801,7 @@ extern void blk_queue_merge_bvec(struct request_queue *, merge_bvec_fn *);
extern void blk_queue_dma_alignment(struct request_queue *, int);
extern void blk_queue_update_dma_alignment(struct request_queue *, int);
extern void blk_queue_softirq_done(struct request_queue *, softirq_done_fn *);
extern void blk_queue_set_discard(struct request_queue *, prepare_discard_fn *);
extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
extern int blk_queue_ordered(struct request_queue *, unsigned, prepare_flush_fn *);
extern int blk_do_ordered(struct request_queue *, struct request **);
@ -837,6 +843,16 @@ static inline struct request *blk_map_queue_find_tag(struct blk_queue_tag *bqt,
}
extern int blkdev_issue_flush(struct block_device *, sector_t *);
extern int blkdev_issue_discard(struct block_device *, sector_t sector,
unsigned nr_sects);
static inline int sb_issue_discard(struct super_block *sb,
sector_t block, unsigned nr_blocks)
{
block <<= (sb->s_blocksize_bits - 9);
nr_blocks <<= (sb->s_blocksize_bits - 9);
return blkdev_issue_discard(sb->s_bdev, block, nr_blocks);
}
/*
* command filter functions

3
include/linux/fs.h
View file

@ -86,7 +86,8 @@ extern int dir_notify_enable;
#define READ_META (READ | (1 << BIO_RW_META))
#define WRITE_SYNC (WRITE | (1 << BIO_RW_SYNC))
#define SWRITE_SYNC (SWRITE | (1 << BIO_RW_SYNC))
#define WRITE_BARRIER ((1 << BIO_RW) | (1 << BIO_RW_BARRIER))
#define WRITE_BARRIER (WRITE | (1 << BIO_RW_BARRIER))
#define WRITE_DISCARD (WRITE | (1 << BIO_RW_DISCARD))
#define SEL_IN 1
#define SEL_OUT 2