block: add io_context->active_ref

Currently ioc->nr_tasks is used to decide two things - whether an ioc
is done issuing IOs and whether it's shared by multiple tasks.  This
patch separate out the first into ioc->active_ref, which is acquired
and released using {get|put}_io_context_active() respectively.

This will be used to associate bio's with a given task.  This patch
doesn't introduce any visible behavior change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 10928740b5dab4366ba6fb728b0a54cf16a41275..439ec21fd787eea2b71fdc798046c392ee96e284 100644 (file)
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -149,20 +149,20 @@ void put_io_context(struct io_context *ioc)
 }
 EXPORT_SYMBOL(put_io_context);
 
-/* Called by the exiting task */
-void exit_io_context(struct task_struct *task)
+/**
+ * put_io_context_active - put active reference on ioc
+ * @ioc: ioc of interest
+ *
+ * Undo get_io_context_active().  If active reference reaches zero after
+ * put, @ioc can never issue further IOs and ioscheds are notified.
+ */
+void put_io_context_active(struct io_context *ioc)
 {
-       struct io_context *ioc;
-       struct io_cq *icq;
        struct hlist_node *n;
        unsigned long flags;
+       struct io_cq *icq;
 
-       task_lock(task);
-       ioc = task->io_context;
-       task->io_context = NULL;
-       task_unlock(task);
-
-       if (!atomic_dec_and_test(&ioc->nr_tasks)) {
+       if (!atomic_dec_and_test(&ioc->active_ref)) {
                put_io_context(ioc);
                return;
        }
@@ -191,6 +191,20 @@ retry:
        put_io_context(ioc);
 }
 
+/* Called by the exiting task */
+void exit_io_context(struct task_struct *task)
+{
+       struct io_context *ioc;
+
+       task_lock(task);
+       ioc = task->io_context;
+       task->io_context = NULL;
+       task_unlock(task);
+
+       atomic_dec(&ioc->nr_tasks);
+       put_io_context_active(ioc);
+}
+
 /**
  * ioc_clear_queue - break any ioc association with the specified queue
  * @q: request_queue being cleared
@@ -223,7 +237,7 @@ int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
 
        /* initialize */
        atomic_long_set(&ioc->refcount, 1);
-       atomic_set(&ioc->nr_tasks, 1);
+       atomic_set(&ioc->active_ref, 1);
        spin_lock_init(&ioc->lock);
        INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
        INIT_HLIST_HEAD(&ioc->icq_list);

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9e386d9bcb798987d18056defb548930caaa9f0d..9a4eac490e0b9371be01a8293bee6ec9f7de6cdf 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1865,7 +1865,7 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
         * task has exited, don't wait
         */
        cic = cfqd->active_cic;
-       if (!cic || !atomic_read(&cic->icq.ioc->nr_tasks))
+       if (!cic || !atomic_read(&cic->icq.ioc->active_ref))
                return;
 
        /*
@@ -2841,7 +2841,7 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 
        if (cfqq->next_rq && (cfqq->next_rq->cmd_flags & REQ_NOIDLE))
                enable_idle = 0;
-       else if (!atomic_read(&cic->icq.ioc->nr_tasks) ||
+       else if (!atomic_read(&cic->icq.ioc->active_ref) ||
                 !cfqd->cfq_slice_idle ||
                 (!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
                enable_idle = 0;

diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 81a8870ac224d8eac76f97a25665bfa6720f86de..6f1a2608e91f36704c9638cb2d84a7f23f95f502 100644 (file)
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -100,6 +100,7 @@ struct io_cq {
  */
 struct io_context {
        atomic_long_t refcount;
+       atomic_t active_ref;
        atomic_t nr_tasks;
 
        /* all the fields below are protected by this lock */
@@ -120,17 +121,34 @@ struct io_context {
        struct work_struct release_work;
 };
 
-static inline void ioc_task_link(struct io_context *ioc)
+/**
+ * get_io_context_active - get active reference on ioc
+ * @ioc: ioc of interest
+ *
+ * Only iocs with active reference can issue new IOs.  This function
+ * acquires an active reference on @ioc.  The caller must already have an
+ * active reference on @ioc.
+ */
+static inline void get_io_context_active(struct io_context *ioc)
 {
        WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
-       WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
+       WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
        atomic_long_inc(&ioc->refcount);
+       atomic_inc(&ioc->active_ref);
+}
+
+static inline void ioc_task_link(struct io_context *ioc)
+{
+       get_io_context_active(ioc);
+
+       WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
        atomic_inc(&ioc->nr_tasks);
 }
 
 struct task_struct;
 #ifdef CONFIG_BLOCK
 void put_io_context(struct io_context *ioc);
+void put_io_context_active(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);