1 files changed, 210 insertions, 235 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index f9fd3dd3916b..08d357522e78 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -10,6 +10,7 @@
 #include <linux/module.h>
 #include <linux/writeback.h>
 #include <linux/device.h>
+#include <trace/events/writeback.h>
 
 static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
 
@@ -49,8 +50,6 @@ static struct timer_list sync_supers_timer;
 static int bdi_sync_supers(void *);
 static void sync_supers_timer_fn(unsigned long);
 
-static void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
-
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
@@ -65,28 +64,21 @@ static void bdi_debug_init(void)
 static int bdi_debug_stats_show(struct seq_file *m, void *v)
 {
         struct backing_dev_info *bdi = m->private;
-        struct bdi_writeback *wb;
+        struct bdi_writeback *wb = &bdi->wb;
         unsigned long background_thresh;
         unsigned long dirty_thresh;
         unsigned long bdi_thresh;
         unsigned long nr_dirty, nr_io, nr_more_io, nr_wb;
         struct inode *inode;
 
-        /*
-         * inode lock is enough here, the bdi->wb_list is protected by
-         * RCU on the reader side
-         */
         nr_wb = nr_dirty = nr_io = nr_more_io = 0;
         spin_lock(&inode_lock);
-        list_for_each_entry(wb, &bdi->wb_list, list) {
-                nr_wb++;
-                list_for_each_entry(inode, &wb->b_dirty, i_list)
-                        nr_dirty++;
-                list_for_each_entry(inode, &wb->b_io, i_list)
-                        nr_io++;
-                list_for_each_entry(inode, &wb->b_more_io, i_list)
-                        nr_more_io++;
-        }
+        list_for_each_entry(inode, &wb->b_dirty, i_list)
+                nr_dirty++;
+        list_for_each_entry(inode, &wb->b_io, i_list)
+                nr_io++;
+        list_for_each_entry(inode, &wb->b_more_io, i_list)
+                nr_more_io++;
         spin_unlock(&inode_lock);
 
         get_dirty_limits(&background_thresh, &dirty_thresh, &bdi_thresh, bdi);
@@ -98,19 +90,16 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
                    "BdiDirtyThresh:   %8lu kB\n"
                    "DirtyThresh:      %8lu kB\n"
                    "BackgroundThresh: %8lu kB\n"
-                   "WritebackThreads: %8lu\n"
                    "b_dirty:          %8lu\n"
                    "b_io:             %8lu\n"
                    "b_more_io:        %8lu\n"
                    "bdi_list:         %8u\n"
-                   "state:            %8lx\n"
-                   "wb_list:          %8u\n",
+                   "state:            %8lx\n",
                    (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
                    (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
                    K(bdi_thresh), K(dirty_thresh),
-                   K(background_thresh), nr_wb, nr_dirty, nr_io, nr_more_io,
-                   !list_empty(&bdi->bdi_list), bdi->state,
-                   !list_empty(&bdi->wb_list));
+                   K(background_thresh), nr_dirty, nr_io, nr_more_io,
+                   !list_empty(&bdi->bdi_list), bdi->state);
 #undef K
 
         return 0;
@@ -247,7 +236,6 @@ static int __init default_bdi_init(void)
         sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
         BUG_ON(IS_ERR(sync_supers_tsk));
 
-        init_timer(&sync_supers_timer);
         setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
         bdi_arm_supers_timer();
 
@@ -259,77 +247,6 @@ static int __init default_bdi_init(void)
 }
 subsys_initcall(default_bdi_init);
 
-static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
-{
-        memset(wb, 0, sizeof(*wb));
-
-        wb->bdi = bdi;
-        wb->last_old_flush = jiffies;
-        INIT_LIST_HEAD(&wb->b_dirty);
-        INIT_LIST_HEAD(&wb->b_io);
-        INIT_LIST_HEAD(&wb->b_more_io);
-}
-
-static void bdi_task_init(struct backing_dev_info *bdi,
-                          struct bdi_writeback *wb)
-{
-        struct task_struct *tsk = current;
-
-        spin_lock(&bdi->wb_lock);
-        list_add_tail_rcu(&wb->list, &bdi->wb_list);
-        spin_unlock(&bdi->wb_lock);
-
-        tsk->flags |= PF_FLUSHER | PF_SWAPWRITE;
-        set_freezable();
-
-        /*
-         * Our parent may run at a different priority, just set us to normal
-         */
-        set_user_nice(tsk, 0);
-}
-
-static int bdi_start_fn(void *ptr)
-{
-        struct bdi_writeback *wb = ptr;
-        struct backing_dev_info *bdi = wb->bdi;
-        int ret;
-
-        /*
-         * Add us to the active bdi_list
-         */
-        spin_lock_bh(&bdi_lock);
-        list_add_rcu(&bdi->bdi_list, &bdi_list);
-        spin_unlock_bh(&bdi_lock);
-
-        bdi_task_init(bdi, wb);
-
-        /*
-         * Clear pending bit and wakeup anybody waiting to tear us down
-         */
-        clear_bit(BDI_pending, &bdi->state);
-        smp_mb__after_clear_bit();
-        wake_up_bit(&bdi->state, BDI_pending);
-
-        ret = bdi_writeback_task(wb);
-
-        /*
-         * Remove us from the list
-         */
-        spin_lock(&bdi->wb_lock);
-        list_del_rcu(&wb->list);
-        spin_unlock(&bdi->wb_lock);
-
-        /*
-         * Flush any work that raced with us exiting. No new work
-         * will be added, since this bdi isn't discoverable anymore.
-         */
-        if (!list_empty(&bdi->work_list))
-                wb_do_writeback(wb, 1);
-
-        wb->task = NULL;
-        return ret;
-}
-
 int bdi_has_dirty_io(struct backing_dev_info *bdi)
 {
         return wb_has_dirty_io(&bdi->wb);
@@ -348,10 +265,10 @@ static void bdi_flush_io(struct backing_dev_info *bdi)
 }
 
 /*
- * kupdated() used to do this. We cannot do it from the bdi_forker_task()
+ * kupdated() used to do this. We cannot do it from the bdi_forker_thread()
  * or we risk deadlocking on ->s_umount. The longer term solution would be
  * to implement sync_supers_bdi() or similar and simply do it from the
- * bdi writeback tasks individually.
+ * bdi writeback thread individually.
  */
 static int bdi_sync_supers(void *unused)
 {
@@ -387,144 +304,198 @@ static void sync_supers_timer_fn(unsigned long unused)
         bdi_arm_supers_timer();
 }
 
-static int bdi_forker_task(void *ptr)
+static void wakeup_timer_fn(unsigned long data)
+{
+        struct backing_dev_info *bdi = (struct backing_dev_info *)data;
+
+        spin_lock_bh(&bdi->wb_lock);
+        if (bdi->wb.task) {
+                trace_writeback_wake_thread(bdi);
+                wake_up_process(bdi->wb.task);
+        } else {
+                /*
+                 * When bdi tasks are inactive for long time, they are killed.
+                 * In this case we have to wake-up the forker thread which
+                 * should create and run the bdi thread.
+                 */
+                trace_writeback_wake_forker_thread(bdi);
+                wake_up_process(default_backing_dev_info.wb.task);
+        }
+        spin_unlock_bh(&bdi->wb_lock);
+}
+
+/*
+ * This function is used when the first inode for this bdi is marked dirty. It
+ * wakes-up the corresponding bdi thread which should then take care of the
+ * periodic background write-out of dirty inodes. Since the write-out would
+ * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
+ * set up a timer which wakes the bdi thread up later.
+ *
+ * Note, we wouldn't bother setting up the timer, but this function is on the
+ * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
+ * by delaying the wake-up.
+ */
+void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
+{
+        unsigned long timeout;
+
+        timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
+        mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
+}
+
+/*
+ * Calculate the longest interval (jiffies) bdi threads are allowed to be
+ * inactive.
+ */
+static unsigned long bdi_longest_inactive(void)
+{
+        unsigned long interval;
+
+        interval = msecs_to_jiffies(dirty_writeback_interval * 10);
+        return max(5UL * 60 * HZ, interval);
+}
+
+static int bdi_forker_thread(void *ptr)
 {
         struct bdi_writeback *me = ptr;
 
-        bdi_task_init(me->bdi, me);
+        current->flags |= PF_FLUSHER | PF_SWAPWRITE;
+        set_freezable();
+
+        /*
+         * Our parent may run at a different priority, just set us to normal
+         */
+        set_user_nice(current, 0);
 
         for (;;) {
-                struct backing_dev_info *bdi, *tmp;
-                struct bdi_writeback *wb;
+                struct task_struct *task = NULL;
+                struct backing_dev_info *bdi;
+                enum {
+                        NO_ACTION,   /* Nothing to do */
+                        FORK_THREAD, /* Fork bdi thread */
+                        KILL_THREAD, /* Kill inactive bdi thread */
+                } action = NO_ACTION;
 
                 /*
                  * Temporary measure, we want to make sure we don't see
                  * dirty data on the default backing_dev_info
                  */
-                if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))
+                if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
+                        del_timer(&me->wakeup_timer);
                         wb_do_writeback(me, 0);
+                }
 
                 spin_lock_bh(&bdi_lock);
+                set_current_state(TASK_INTERRUPTIBLE);
 
-                /*
-                 * Check if any existing bdi's have dirty data without
-                 * a thread registered. If so, set that up.
-                 */
-                list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
-                        if (bdi->wb.task)
-                                continue;
-                        if (list_empty(&bdi->work_list) &&
-                            !bdi_has_dirty_io(bdi))
+                list_for_each_entry(bdi, &bdi_list, bdi_list) {
+                        bool have_dirty_io;
+
+                        if (!bdi_cap_writeback_dirty(bdi) ||
+                             bdi_cap_flush_forker(bdi))
                                 continue;
 
-                        bdi_add_default_flusher_task(bdi);
-                }
+                        WARN(!test_bit(BDI_registered, &bdi->state),
+                             "bdi %p/%s is not registered!\n", bdi, bdi->name);
 
-                set_current_state(TASK_INTERRUPTIBLE);
+                        have_dirty_io = !list_empty(&bdi->work_list) ||
+                                        wb_has_dirty_io(&bdi->wb);
 
-                if (list_empty(&bdi_pending_list)) {
-                        unsigned long wait;
+                        /*
+                         * If the bdi has work to do, but the thread does not
+                         * exist - create it.
+                         */
+                        if (!bdi->wb.task && have_dirty_io) {
+                                /*
+                                 * Set the pending bit - if someone will try to
+                                 * unregister this bdi - it'll wait on this bit.
+                                 */
+                                set_bit(BDI_pending, &bdi->state);
+                                action = FORK_THREAD;
+                                break;
+                        }
+
+                        spin_lock(&bdi->wb_lock);
+
+                        /*
+                         * If there is no work to do and the bdi thread was
+                         * inactive long enough - kill it. The wb_lock is taken
+                         * to make sure no-one adds more work to this bdi and
+                         * wakes the bdi thread up.
+                         */
+                        if (bdi->wb.task && !have_dirty_io &&
+                            time_after(jiffies, bdi->wb.last_active +
+                                                bdi_longest_inactive())) {
+                                task = bdi->wb.task;
+                                bdi->wb.task = NULL;
+                                spin_unlock(&bdi->wb_lock);
+                                set_bit(BDI_pending, &bdi->state);
+                                action = KILL_THREAD;
+                                break;
+                        }
+                        spin_unlock(&bdi->wb_lock);
+                }
+                spin_unlock_bh(&bdi_lock);
 
-                        spin_unlock_bh(&bdi_lock);
-                        wait = msecs_to_jiffies(dirty_writeback_interval * 10);
-                        if (wait)
-                                schedule_timeout(wait);
+                /* Keep working if default bdi still has things to do */
+                if (!list_empty(&me->bdi->work_list))
+                        __set_current_state(TASK_RUNNING);
+
+                switch (action) {
+                case FORK_THREAD:
+                        __set_current_state(TASK_RUNNING);
+                        task = kthread_run(bdi_writeback_thread, &bdi->wb, "flush-%s",
+                                           dev_name(bdi->dev));
+                        if (IS_ERR(task)) {
+                                /*
+                                 * If thread creation fails, force writeout of
+                                 * the bdi from the thread.
+                                 */
+                                bdi_flush_io(bdi);
+                        } else {
+                                /*
+                                 * The spinlock makes sure we do not lose
+                                 * wake-ups when racing with 'bdi_queue_work()'.
+                                 */
+                                spin_lock_bh(&bdi->wb_lock);
+                                bdi->wb.task = task;
+                                spin_unlock_bh(&bdi->wb_lock);
+                        }
+                        break;
+
+                case KILL_THREAD:
+                        __set_current_state(TASK_RUNNING);
+                        kthread_stop(task);
+                        break;
+
+                case NO_ACTION:
+                        if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
+                                /*
+                                 * There are no dirty data. The only thing we
+                                 * should now care about is checking for
+                                 * inactive bdi threads and killing them. Thus,
+                                 * let's sleep for longer time, save energy and
+                                 * be friendly for battery-driven devices.
+                                 */
+                                schedule_timeout(bdi_longest_inactive());
                         else
-                                schedule();
+                                schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
                         try_to_freeze();
+                        /* Back to the main loop */
                         continue;
                 }
 
-                __set_current_state(TASK_RUNNING);
-
-                /*
-                 * This is our real job - check for pending entries in
-                 * bdi_pending_list, and create the tasks that got added
-                 */
-                bdi = list_entry(bdi_pending_list.next, struct backing_dev_info,
-                                 bdi_list);
-                list_del_init(&bdi->bdi_list);
-                spin_unlock_bh(&bdi_lock);
-
-                wb = &bdi->wb;
-                wb->task = kthread_run(bdi_start_fn, wb, "flush-%s",
-                                        dev_name(bdi->dev));
                 /*
-                 * If task creation fails, then readd the bdi to
-                 * the pending list and force writeout of the bdi
-                 * from this forker thread. That will free some memory
-                 * and we can try again.
+                 * Clear pending bit and wakeup anybody waiting to tear us down.
                  */
-                if (IS_ERR(wb->task)) {
-                        wb->task = NULL;
-
-                        /*
-                         * Add this 'bdi' to the back, so we get
-                         * a chance to flush other bdi's to free
-                         * memory.
-                         */
-                        spin_lock_bh(&bdi_lock);
-                        list_add_tail(&bdi->bdi_list, &bdi_pending_list);
-                        spin_unlock_bh(&bdi_lock);
-
-                        bdi_flush_io(bdi);
-                }
+                clear_bit(BDI_pending, &bdi->state);
+                smp_mb__after_clear_bit();
+                wake_up_bit(&bdi->state, BDI_pending);
         }
 
         return 0;
 }
 
-static void bdi_add_to_pending(struct rcu_head *head)
-{
-        struct backing_dev_info *bdi;
-
-        bdi = container_of(head, struct backing_dev_info, rcu_head);
-        INIT_LIST_HEAD(&bdi->bdi_list);
-
-        spin_lock(&bdi_lock);
-        list_add_tail(&bdi->bdi_list, &bdi_pending_list);
-        spin_unlock(&bdi_lock);
-
-        /*
-         * We are now on the pending list, wake up bdi_forker_task()
-         * to finish the job and add us back to the active bdi_list
-         */
-        wake_up_process(default_backing_dev_info.wb.task);
-}
-
-/*
- * Add the default flusher task that gets created for any bdi
- * that has dirty data pending writeout
- */
-void static bdi_add_default_flusher_task(struct backing_dev_info *bdi)
-{
-        if (!bdi_cap_writeback_dirty(bdi))
-                return;
-
-        if (WARN_ON(!test_bit(BDI_registered, &bdi->state))) {
-                printk(KERN_ERR "bdi %p/%s is not registered!\n",
-                                                        bdi, bdi->name);
-                return;
-        }
-
-        /*
-         * Check with the helper whether to proceed adding a task. Will only
-         * abort if we two or more simultanous calls to
-         * bdi_add_default_flusher_task() occured, further additions will block
-         * waiting for previous additions to finish.
-         */
-        if (!test_and_set_bit(BDI_pending, &bdi->state)) {
-                list_del_rcu(&bdi->bdi_list);
-
-                /*
-                 * We must wait for the current RCU period to end before
-                 * moving to the pending list. So schedule that operation
-                 * from an RCU callback.
-                 */
-                call_rcu(&bdi->rcu_head, bdi_add_to_pending);
-        }
-}
-
 /*
  * Remove bdi from bdi_list, and ensure that it is no longer visible
  */
@@ -541,23 +512,16 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
                 const char *fmt, ...)
 {
         va_list args;
-        int ret = 0;
         struct device *dev;
 
         if (bdi->dev)   /* The driver needs to use separate queues per device */
-                goto exit;
+                return 0;
 
         va_start(args, fmt);
         dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
         va_end(args);
-        if (IS_ERR(dev)) {
-                ret = PTR_ERR(dev);
-                goto exit;
-        }
-
-        spin_lock_bh(&bdi_lock);
-        list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
-        spin_unlock_bh(&bdi_lock);
+        if (IS_ERR(dev))
+                return PTR_ERR(dev);
 
         bdi->dev = dev;
 
@@ -569,21 +533,21 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
         if (bdi_cap_flush_forker(bdi)) {
                 struct bdi_writeback *wb = &bdi->wb;
 
-                wb->task = kthread_run(bdi_forker_task, wb, "bdi-%s",
+                wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",
                                                 dev_name(dev));
-                if (IS_ERR(wb->task)) {
-                        wb->task = NULL;
-                        ret = -ENOMEM;
-
-                        bdi_remove_from_list(bdi);
-                        goto exit;
-                }
+                if (IS_ERR(wb->task))
+                        return PTR_ERR(wb->task);
         }
 
         bdi_debug_register(bdi, dev_name(dev));
         set_bit(BDI_registered, &bdi->state);
-exit:
-        return ret;
+
+        spin_lock_bh(&bdi_lock);
+        list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
+        spin_unlock_bh(&bdi_lock);
+
+        trace_writeback_bdi_register(bdi);
+        return 0;
 }
 EXPORT_SYMBOL(bdi_register);
 
@@ -598,31 +562,29 @@ EXPORT_SYMBOL(bdi_register_dev);
  */
 static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 {
-        struct bdi_writeback *wb;
-
         if (!bdi_cap_writeback_dirty(bdi))
                 return;
 
         /*
-         * If setup is pending, wait for that to complete first
+         * Make sure nobody finds us on the bdi_list anymore
          */
-        wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
-                        TASK_UNINTERRUPTIBLE);
+        bdi_remove_from_list(bdi);
 
         /*
-         * Make sure nobody finds us on the bdi_list anymore
+         * If setup is pending, wait for that to complete first
          */
-        bdi_remove_from_list(bdi);
+        wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
+                        TASK_UNINTERRUPTIBLE);
 
         /*
-         * Finally, kill the kernel threads. We don't need to be RCU
+         * Finally, kill the kernel thread. We don't need to be RCU
          * safe anymore, since the bdi is gone from visibility. Force
          * unfreeze of the thread before calling kthread_stop(), otherwise
          * it would never exet if it is currently stuck in the refrigerator.
          */
-        list_for_each_entry(wb, &bdi->wb_list, list) {
-                thaw_process(wb->task);
-                kthread_stop(wb->task);
+        if (bdi->wb.task) {
+                thaw_process(bdi->wb.task);
+                kthread_stop(bdi->wb.task);
         }
 }
 
@@ -644,7 +606,9 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
 void bdi_unregister(struct backing_dev_info *bdi)
 {
         if (bdi->dev) {
+                trace_writeback_bdi_unregister(bdi);
                 bdi_prune_sb(bdi);
+                del_timer_sync(&bdi->wb.wakeup_timer);
 
                 if (!bdi_cap_flush_forker(bdi))
                         bdi_wb_shutdown(bdi);
@@ -655,6 +619,18 @@ void bdi_unregister(struct backing_dev_info *bdi)
 }
 EXPORT_SYMBOL(bdi_unregister);
 
+static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
+{
+        memset(wb, 0, sizeof(*wb));
+
+        wb->bdi = bdi;
+        wb->last_old_flush = jiffies;
+        INIT_LIST_HEAD(&wb->b_dirty);
+        INIT_LIST_HEAD(&wb->b_io);
+        INIT_LIST_HEAD(&wb->b_more_io);
+        setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
+}
+
 int bdi_init(struct backing_dev_info *bdi)
 {
         int i, err;
@@ -666,7 +642,6 @@ int bdi_init(struct backing_dev_info *bdi)
         bdi->max_prop_frac = PROP_FRAC_BASE;
         spin_lock_init(&bdi->wb_lock);
         INIT_LIST_HEAD(&bdi->bdi_list);
-        INIT_LIST_HEAD(&bdi->wb_list);
         INIT_LIST_HEAD(&bdi->work_list);
 
         bdi_wb_init(&bdi->wb, bdi);