Reduce number of arc_prune threads

On FreeBSD vnode reclamation is single-threaded, protected by single
global lock.  Linux seems to be able to use a thread per mount point,
but at this time it creates more harm than good.

Reduce number of threads to 1, adding tunable in case somebody wants
to try more.

Reviewed-by: Ryan Moeller <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Chris Dunlop <[email protected]>
Reviewed-by: Ahelenia Ziemiańska <[email protected]>
Signed-off-by: Alexander Motin <[email protected]>
Closes #12896
Issue #9966

0 files changed, 0 insertions, 0 deletions