fscache: convert object to use workqueue instead of slow-work

Make fscache object state transition callbacks use workqueue instead
of slow-work.  New dedicated unbound CPU workqueue fscache_object_wq
is created.  get/put callbacks are renamed and modified to take
@object and called directly from the enqueue wrapper and the work
function.  While at it, make all open coded instances of get/put to
use fscache_get/put_object().

* Unbound workqueue is used.

* work_busy() output is printed instead of slow-work flags in object
  debugging outputs.  They mean basically the same thing bit-for-bit.

* sysctl fscache.object_max_active added to control concurrency.  The
  default value is nr_cpus clamped between 4 and
  WQ_UNBOUND_MAX_ACTIVE.

* slow_work_sleep_till_thread_needed() is replaced with fscache
  private implementation fscache_object_sleep_till_congested() which
  waits on fscache_object_wq congestion.

* debugfs support is dropped for now.  Tracing API based debug
  facility is planned to be added.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Howells <dhowells@redhat.com>
diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c
index 4a8eb31..ebe29c5 100644
--- a/fs/fscache/object-list.c
+++ b/fs/fscache/object-list.c
@@ -34,8 +34,8 @@
 #define FSCACHE_OBJLIST_CONFIG_NOREADS	0x00000200	/* show objects without active reads */
 #define FSCACHE_OBJLIST_CONFIG_EVENTS	0x00000400	/* show objects with events */
 #define FSCACHE_OBJLIST_CONFIG_NOEVENTS	0x00000800	/* show objects without no events */
-#define FSCACHE_OBJLIST_CONFIG_WORK	0x00001000	/* show objects with slow work */
-#define FSCACHE_OBJLIST_CONFIG_NOWORK	0x00002000	/* show objects without slow work */
+#define FSCACHE_OBJLIST_CONFIG_WORK	0x00001000	/* show objects with work */
+#define FSCACHE_OBJLIST_CONFIG_NOWORK	0x00002000	/* show objects without work */
 
 	u8		buf[512];	/* key and aux data buffer */
 };
@@ -231,12 +231,11 @@
 		       READS, NOREADS);
 		FILTER(obj->events & obj->event_mask,
 		       EVENTS, NOEVENTS);
-		FILTER(obj->work.flags & ~(1UL << SLOW_WORK_VERY_SLOW),
-		       WORK, NOWORK);
+		FILTER(work_busy(&obj->work), WORK, NOWORK);
 	}
 
 	seq_printf(m,
-		   "%8x %8x %s %5u %3u %3u %3u %2u %5u %2lx %2lx %1lx %1lx | ",
+		   "%8x %8x %s %5u %3u %3u %3u %2u %5u %2lx %2lx %1lx %1x | ",
 		   obj->debug_id,
 		   obj->parent ? obj->parent->debug_id : -1,
 		   fscache_object_states_short[obj->state],
@@ -249,7 +248,7 @@
 		   obj->event_mask & FSCACHE_OBJECT_EVENTS_MASK,
 		   obj->events,
 		   obj->flags,
-		   obj->work.flags);
+		   work_busy(&obj->work));
 
 	no_cookie = true;
 	keylen = auxlen = 0;