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dm mpath: push back requests instead of queueing
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There is no reason why multipath needs to queue requests internally for
queue_if_no_path or pg_init; we should rather push them back onto the
request queue.

And while we're at it we can simplify the conditional statement in
map_io() to make it easier to read.

Since mpath no longer does internal queuing of I/O the table info no
longer emits the internal queue_size.  Instead it displays 1 if queuing
is being used or 0 if it is not.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
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Hannes Reinecke authored and Mike Snitzer committed Mar 27, 2014
1 parent 9974fa2 commit e809917
Showing 1 changed file with 36 additions and 78 deletions.
114 changes: 36 additions & 78 deletions drivers/md/dm-mpath.c
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Original file line number Diff line number Diff line change
Expand Up @@ -93,9 +93,7 @@ struct multipath {
unsigned pg_init_count; /* Number of times pg_init called */
unsigned pg_init_delay_msecs; /* Number of msecs before pg_init retry */

unsigned queue_size;
struct work_struct process_queued_ios;
struct list_head queued_ios;

struct work_struct trigger_event;

Expand Down Expand Up @@ -124,6 +122,7 @@ static struct workqueue_struct *kmultipathd, *kmpath_handlerd;
static void process_queued_ios(struct work_struct *work);
static void trigger_event(struct work_struct *work);
static void activate_path(struct work_struct *work);
static int __pgpath_busy(struct pgpath *pgpath);


/*-----------------------------------------------
Expand Down Expand Up @@ -195,7 +194,6 @@ static struct multipath *alloc_multipath(struct dm_target *ti)
m = kzalloc(sizeof(*m), GFP_KERNEL);
if (m) {
INIT_LIST_HEAD(&m->priority_groups);
INIT_LIST_HEAD(&m->queued_ios);
spin_lock_init(&m->lock);
m->queue_io = 1;
m->pg_init_delay_msecs = DM_PG_INIT_DELAY_DEFAULT;
Expand Down Expand Up @@ -368,12 +366,15 @@ static void __choose_pgpath(struct multipath *m, size_t nr_bytes)
*/
static int __must_push_back(struct multipath *m)
{
return (m->queue_if_no_path != m->saved_queue_if_no_path &&
dm_noflush_suspending(m->ti));
return (m->queue_if_no_path ||
(m->queue_if_no_path != m->saved_queue_if_no_path &&
dm_noflush_suspending(m->ti)));
}

#define pg_ready(m) (!(m)->queue_io && !(m)->pg_init_required)

static int map_io(struct multipath *m, struct request *clone,
union map_info *map_context, unsigned was_queued)
union map_info *map_context)
{
int r = DM_MAPIO_REMAPPED;
size_t nr_bytes = blk_rq_bytes(clone);
Expand All @@ -391,37 +392,28 @@ static int map_io(struct multipath *m, struct request *clone,

pgpath = m->current_pgpath;

if (was_queued)
m->queue_size--;

if (m->pg_init_required) {
if (!m->pg_init_in_progress)
queue_work(kmultipathd, &m->process_queued_ios);
r = DM_MAPIO_REQUEUE;
} else if ((pgpath && m->queue_io) ||
(!pgpath && m->queue_if_no_path)) {
/* Queue for the daemon to resubmit */
list_add_tail(&clone->queuelist, &m->queued_ios);
m->queue_size++;
if (!m->queue_io)
queue_work(kmultipathd, &m->process_queued_ios);
pgpath = NULL;
r = DM_MAPIO_SUBMITTED;
} else if (pgpath) {
bdev = pgpath->path.dev->bdev;
clone->q = bdev_get_queue(bdev);
clone->rq_disk = bdev->bd_disk;
} else if (__must_push_back(m))
r = DM_MAPIO_REQUEUE;
else
r = -EIO; /* Failed */

mpio->pgpath = pgpath;
mpio->nr_bytes = nr_bytes;

if (r == DM_MAPIO_REMAPPED && pgpath->pg->ps.type->start_io)
pgpath->pg->ps.type->start_io(&pgpath->pg->ps, &pgpath->path,
nr_bytes);
if (pgpath) {
if (pg_ready(m)) {
bdev = pgpath->path.dev->bdev;
clone->q = bdev_get_queue(bdev);
clone->rq_disk = bdev->bd_disk;
mpio->pgpath = pgpath;
mpio->nr_bytes = nr_bytes;
if (pgpath->pg->ps.type->start_io)
pgpath->pg->ps.type->start_io(&pgpath->pg->ps,
&pgpath->path,
nr_bytes);
} else {
__pg_init_all_paths(m);
r = DM_MAPIO_REQUEUE;
}
} else {
/* No path */
if (__must_push_back(m))
r = DM_MAPIO_REQUEUE;
else
r = -EIO; /* Failed */
}

spin_unlock_irqrestore(&m->lock, flags);

Expand All @@ -443,48 +435,14 @@ static int queue_if_no_path(struct multipath *m, unsigned queue_if_no_path,
else
m->saved_queue_if_no_path = queue_if_no_path;
m->queue_if_no_path = queue_if_no_path;
if (!m->queue_if_no_path && m->queue_size)
if (!m->queue_if_no_path)
queue_work(kmultipathd, &m->process_queued_ios);

spin_unlock_irqrestore(&m->lock, flags);

return 0;
}

/*-----------------------------------------------------------------
* The multipath daemon is responsible for resubmitting queued ios.
*---------------------------------------------------------------*/

static void dispatch_queued_ios(struct multipath *m)
{
int r;
unsigned long flags;
union map_info *info;
struct request *clone, *n;
LIST_HEAD(cl);

spin_lock_irqsave(&m->lock, flags);
list_splice_init(&m->queued_ios, &cl);
spin_unlock_irqrestore(&m->lock, flags);

list_for_each_entry_safe(clone, n, &cl, queuelist) {
list_del_init(&clone->queuelist);

info = dm_get_rq_mapinfo(clone);

r = map_io(m, clone, info, 1);
if (r < 0) {
clear_mapinfo(m, info);
dm_kill_unmapped_request(clone, r);
} else if (r == DM_MAPIO_REMAPPED)
dm_dispatch_request(clone);
else if (r == DM_MAPIO_REQUEUE) {
clear_mapinfo(m, info);
dm_requeue_unmapped_request(clone);
}
}
}

static void process_queued_ios(struct work_struct *work)
{
struct multipath *m =
Expand All @@ -509,7 +467,7 @@ static void process_queued_ios(struct work_struct *work)

spin_unlock_irqrestore(&m->lock, flags);
if (!must_queue)
dispatch_queued_ios(m);
dm_table_run_md_queue_async(m->ti->table);
}

/*
Expand Down Expand Up @@ -987,7 +945,7 @@ static int multipath_map(struct dm_target *ti, struct request *clone,
return DM_MAPIO_REQUEUE;

clone->cmd_flags |= REQ_FAILFAST_TRANSPORT;
r = map_io(m, clone, map_context, 0);
r = map_io(m, clone, map_context);
if (r < 0 || r == DM_MAPIO_REQUEUE)
clear_mapinfo(m, map_context);

Expand Down Expand Up @@ -1056,7 +1014,7 @@ static int reinstate_path(struct pgpath *pgpath)

pgpath->is_active = 1;

if (!m->nr_valid_paths++ && m->queue_size) {
if (!m->nr_valid_paths++) {
m->current_pgpath = NULL;
queue_work(kmultipathd, &m->process_queued_ios);
} else if (m->hw_handler_name && (m->current_pg == pgpath->pg)) {
Expand Down Expand Up @@ -1435,7 +1393,7 @@ static void multipath_status(struct dm_target *ti, status_type_t type,

/* Features */
if (type == STATUSTYPE_INFO)
DMEMIT("2 %u %u ", m->queue_size, m->pg_init_count);
DMEMIT("2 %u %u ", m->queue_io, m->pg_init_count);
else {
DMEMIT("%u ", m->queue_if_no_path +
(m->pg_init_retries > 0) * 2 +
Expand Down Expand Up @@ -1686,7 +1644,7 @@ static int multipath_busy(struct dm_target *ti)
spin_lock_irqsave(&m->lock, flags);

/* pg_init in progress, requeue until done */
if (m->pg_init_in_progress) {
if (!pg_ready(m)) {
busy = 1;
goto out;
}
Expand Down Expand Up @@ -1739,7 +1697,7 @@ static int multipath_busy(struct dm_target *ti)
*---------------------------------------------------------------*/
static struct target_type multipath_target = {
.name = "multipath",
.version = {1, 6, 0},
.version = {1, 7, 0},
.module = THIS_MODULE,
.ctr = multipath_ctr,
.dtr = multipath_dtr,
Expand Down

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