Commit b63349a7 authored Oct 01, 2013 by Hannes Reinecke Committed by Mike Snitzer Nov 05, 2013

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>

parent 954a73d5

drivers/md/dm-mpath.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -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) \|\|
		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;

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