mm/slub: Avoid waiting on empty per-cpu sheaf replacement

mm/slub: Avoid waiting on empty per-cpu sheaf replacement

When the per-cpu sheaf is empty, attempt to replace it with a full one
from the barn.  If the barn lock is contended then fail quickly and
enter the recovery code that will refill the empty sheaf.

This is to avoid congestion on the barn in the event of many tasks
requesting allocations at the same time.  Discovered by brk1_processes()
regression from will-it-scale benchmarks.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>