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>
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 799e479..6eb9dc9 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -391,13 +391,16 @@
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 @@
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;