block: strip out locking optimization in put_io_context()

put_io_context() performed a complex trylock dancing to avoid
deferring ioc release to workqueue.  It was also broken on UP because
trylock was always assumed to succeed which resulted in unbalanced
preemption count.

While there are ways to fix the UP breakage, even the most
pathological microbench (forced ioc allocation and tight fork/exit
loop) fails to show any appreciable performance benefit of the
optimization.  Strip it out.  If there turns out to be workloads which
are affected by this change, simpler optimization from the discussion
thread can be applied later.

Signed-off-by: Tejun Heo <tj@kernel.org>
LKML-Reference: <1328514611.21268.66.camel@sli10-conroe>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 2 insertions, 6 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 6c6a1f008065..606cf339bb56 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -399,9 +399,6 @@ struct request_queue {
         /* Throttle data */
         struct throtl_data *td;
 #endif
-#ifdef CONFIG_LOCKDEP
-        int                     ioc_release_depth;
-#endif
 };
 
 #define QUEUE_FLAG_QUEUED       1       /* uses generic tag queueing */
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 7e1371c4bccf..119773eebe31 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -133,7 +133,7 @@ static inline struct io_context *ioc_task_link(struct io_context *ioc)
 
 struct task_struct;
 #ifdef CONFIG_BLOCK
-void put_io_context(struct io_context *ioc, struct request_queue *locked_q);
+void put_io_context(struct io_context *ioc);
 void exit_io_context(struct task_struct *task);
 struct io_context *get_task_io_context(struct task_struct *task,
                                        gfp_t gfp_flags, int node);
@@ -141,8 +141,7 @@ void ioc_ioprio_changed(struct io_context *ioc, int ioprio);
 void ioc_cgroup_changed(struct io_context *ioc);
 #else
 struct io_context;
-static inline void put_io_context(struct io_context *ioc,
-                                  struct request_queue *locked_q) { }
+static inline void put_io_context(struct io_context *ioc) { }
 static inline void exit_io_context(struct task_struct *task) { }
 #endif