[dm-devel] dm: do not call dm_sync_table() when creating new devices

[Mike Snitzer]

On Wed, Nov 05 2014 at  8:35am -0500,
Hannes Reinecke <hare at suse.de> wrote:

> When creating new devices dm_sync_table() calls
> synchronize_rcu_expedited(), causing _all_ pending
> RCU pointers to be flushed. This causes a latency
> overhead 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 at suse.de>

Looks good, I'll get it staged for 3.19 (will need to be rebased on the
linux-dm.git 'dm-for-3.19' branch given the suspend related refactoring
there, but I'll take care of it as needed).