LRU queue lanes have partitions (lexical change only).

The LRU queue isn't subject to fragmentation, and the "fragments"
{X lanes} partition the queue, so call these partitions.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
LRU cleanup queue.

Defer cache entry cleanup processing to the LRU thread.
Define cleanup queue and implement cache_inode_lru_cleanup_push.
Implement cleanup processing in LRU thread.  Use new cleanup
mechanism in cache_inode_kill_entry.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Remove pthread_wrlock_trylock in state_wipe_file.

The function is now called only from the LRU thread, in
deferred cleanup processing.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Streamline atomics in cache_inode_lru.

The code holds lru->mtx (modulo the one special case) in all
the paths where lru->refcount is inc/decremented, so we
should just use ordinary increment or decrement.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>