dm: do not call dm_sync_table() when creating new devices (41abc4e1) · Commits · 戴 / test

When creating new devices dm_sync_table() calls synchronize_rcu_expedited(), causing _all_ pending RCU pointers to be flushed. This causes a latency overhead that is especially noticeable when creating lots of devices. And all of this is pointless as there are no old maps to be disconnected, and hence no stale pointers which would need to be cleared up. Signed-off-by:

Hannes Reinecke <hare@suse.de> Reviewed-by:

Mikulas Patocka <mpatocka@redhat.com> Signed-off-by:

Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -2341,6 +2341,7 @@ static struct dm_table __bind(struct mapped_device md, struct dm_table *t,
		set_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
		else
		clear_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
		if (old_map)
		dm_sync_table(md);

		return old_map;
		@@ -2782,6 +2783,7 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
		* flush_workqueue(md->wq).
		*/
		set_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
		if (map)
		synchronize_srcu(&md->io_barrier);

		/*
		@@ -2802,6 +2804,7 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)

		if (noflush)
		clear_bit(DMF_NOFLUSH_SUSPENDING, &md->flags);
		if (map)
		synchronize_srcu(&md->io_barrier);

		/* were we interrupted ? */

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