dm mpath: requeue I/O during pg_init

When pg_init is running no I/O can be submitted to the underlying
devices, as the path priority etc might change.  When using queue_io for
this, requests will be piling up within multipath as the block I/O
scheduler just sees a _very fast_ device.  All of this queued I/O has to
be resubmitted from within multipathing once pg_init is done.

This approach has the problem that it's virtually impossible to
abort I/O when pg_init is running, and we're adding heavy load
to the devices after pg_init since all of the queued I/O needs to be
resubmitted _before_ any requests can be pulled off of the request queue
and normal operation continues.

This patch will requeue the I/O that triggers the pg_init call, and
return 'busy' when pg_init is in progress.  With these changes the block
I/O scheduler will stop submitting I/O during pg_init, resulting in a
quicker path switch and less I/O pressure (and memory consumption) after
pg_init.

Signed-off-by: Hannes Reinecke <hare@suse.de>
[patch header edited for clarity and typos by Mike Snitzer]
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 799e479db93b..6eb9dc9ef8f3 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -391,13 +391,16 @@ static int map_io(struct multipath *m, struct request *clone,
         if (was_queued)
                 m->queue_size--;
 
-        if ((pgpath && m->queue_io) ||
-            (!pgpath && m->queue_if_no_path)) {
+        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->pg_init_required && !m->pg_init_in_progress) ||
-                    !m->queue_io)
+                if (!m->queue_io)
                         queue_work(kmultipathd, &m->process_queued_ios);
                 pgpath = NULL;
                 r = DM_MAPIO_SUBMITTED;
@@ -1677,6 +1680,11 @@ 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) {
+                busy = 1;
+                goto out;
+        }
         /* Guess which priority_group will be used at next mapping time */
         if (unlikely(!m->current_pgpath && m->next_pg))
                 pg = m->next_pg;