speeding up zfs snapshot listing

[mike tancsa]

We have a backup server that has a fair amount of zfs snapshots--
currently at 30,000+... To list them all takes about 20 seconds after
caching, but can take upto a minute after boot up, or if the metadata
has been evicted from ARC.  Are there any tunings that can be done to to
speed up the listing or at least make sure the metadata gets cached as
best as possible ? We have a nagios check 4 times a day to make sure
backups are running and fresh that sometimes times out.  We will
probably end up close to 50 to 60k worth of snapshots soon. 

The 20 seconds to list, seems to be all CPU bound. Looking at gstat zfs
list -t snapshot is not hitting the disk.  So not sure if anything can
be done tuning wise ?

    ---Mike