1 files changed, 5 insertions, 12 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 025a63894cf0..fddd8abd839a 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -255,6 +255,7 @@ static void wb_wait_for_completion(struct backing_dev_info *bdi,
                                         /* if foreign slots >= 8, switch */
 #define WB_FRN_HIST_MAX_SLOTS   (WB_FRN_HIST_THR_SLOTS / 2 + 1)
                                         /* one round can affect upto 5 slots */
+#define WB_FRN_MAX_IN_FLIGHT    1024    /* don't queue too many concurrently */
 
 static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
 static struct workqueue_struct *isw_wq;
@@ -507,18 +508,13 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id)
         if (inode->i_state & I_WB_SWITCH)
                 return;
 
-        /*
-         * Avoid starting new switches while sync_inodes_sb() is in
-         * progress.  Otherwise, if the down_write protected issue path
-         * blocks heavily, we might end up starting a large number of
-         * switches which will block on the rwsem.
-         */
-        if (!down_read_trylock(&bdi->wb_switch_rwsem))
+        /* avoid queueing a new switch if too many are already in flight */
+        if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
                 return;
 
         isw = kzalloc(sizeof(*isw), GFP_ATOMIC);
         if (!isw)
-                goto out_unlock;
+                return;
 
         /* find and pin the new wb */
         rcu_read_lock();
@@ -552,15 +548,12 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id)
         call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn);
 
         atomic_inc(&isw_nr_in_flight);
-
-        goto out_unlock;
+        return;
 
 out_free:
         if (isw->new_wb)
                 wb_put(isw->new_wb);
         kfree(isw);
-out_unlock:
-        up_read(&bdi->wb_switch_rwsem);
 }
 
 /**