1 files changed, 59 insertions, 2 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 55627306abe0..5ad3c106606b 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -729,6 +729,7 @@ static wait_queue_head_t congestion_wqh[2] = {
                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
         };
+static atomic_t nr_bdi_congested[2];
 
 void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
 {
@@ -736,7 +737,8 @@ void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
         wait_queue_head_t *wqh = &congestion_wqh[sync];
 
         bit = sync ? BDI_sync_congested : BDI_async_congested;
-        clear_bit(bit, &bdi->state);
+        if (test_and_clear_bit(bit, &bdi->state))
+                atomic_dec(&nr_bdi_congested[sync]);
         smp_mb__after_clear_bit();
         if (waitqueue_active(wqh))
                 wake_up(wqh);
@@ -748,7 +750,8 @@ void set_bdi_congested(struct backing_dev_info *bdi, int sync)
         enum bdi_state bit;
 
         bit = sync ? BDI_sync_congested : BDI_async_congested;
-        set_bit(bit, &bdi->state);
+        if (!test_and_set_bit(bit, &bdi->state))
+                atomic_inc(&nr_bdi_congested[sync]);
 }
 EXPORT_SYMBOL(set_bdi_congested);
 
@@ -779,3 +782,57 @@ long congestion_wait(int sync, long timeout)
 }
 EXPORT_SYMBOL(congestion_wait);
 
+/**
+ * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
+ * @zone: A zone to check if it is heavily congested
+ * @sync: SYNC or ASYNC IO
+ * @timeout: timeout in jiffies
+ *
+ * In the event of a congested backing_dev (any backing_dev) and the given
+ * @zone has experienced recent congestion, this waits for up to @timeout
+ * jiffies for either a BDI to exit congestion of the given @sync queue
+ * or a write to complete.
+ *
+ * In the absense of zone congestion, cond_resched() is called to yield
+ * the processor if necessary but otherwise does not sleep.
+ *
+ * The return value is 0 if the sleep is for the full timeout. Otherwise,
+ * it is the number of jiffies that were still remaining when the function
+ * returned. return_value == timeout implies the function did not sleep.
+ */
+long wait_iff_congested(struct zone *zone, int sync, long timeout)
+{
+        long ret;
+        unsigned long start = jiffies;
+        DEFINE_WAIT(wait);
+        wait_queue_head_t *wqh = &congestion_wqh[sync];
+
+        /*
+         * If there is no congestion, or heavy congestion is not being
+         * encountered in the current zone, yield if necessary instead
+         * of sleeping on the congestion queue
+         */
+        if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
+                        !zone_is_reclaim_congested(zone)) {
+                cond_resched();
+
+                /* In case we scheduled, work out time remaining */
+                ret = timeout - (jiffies - start);
+                if (ret < 0)
+                        ret = 0;
+
+                goto out;
+        }
+
+        /* Sleep until uncongested or a write happens */
+        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
+        ret = io_schedule_timeout(timeout);
+        finish_wait(wqh, &wait);
+
+out:
+        trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
+                                        jiffies_to_usecs(jiffies - start));
+
+        return ret;
+}
+EXPORT_SYMBOL(wait_iff_congested);