1 files changed, 17 insertions, 2 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 53e4534885ad..5a8776eb0f43 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1439,6 +1439,19 @@ putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
 }
 
 /*
+ * If a kernel thread (such as nfsd for loop-back mounts) services
+ * a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
+ * In that case we should only throttle if the backing device it is
+ * writing to is congested.  In other cases it is safe to throttle.
+ */
+static int current_may_throttle(void)
+{
+        return !(current->flags & PF_LESS_THROTTLE) ||
+                current->backing_dev_info == NULL ||
+                bdi_write_congested(current->backing_dev_info);
+}
+
+/*
  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
  * of reclaimed pages
  */
@@ -1566,7 +1579,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
                  * implies that pages are cycling through the LRU faster than
                  * they are written so also forcibly stall.
                  */
-                if (nr_unqueued_dirty == nr_taken || nr_immediate)
+                if ((nr_unqueued_dirty == nr_taken || nr_immediate) &&
+                    current_may_throttle())
                         congestion_wait(BLK_RW_ASYNC, HZ/10);
         }
 
@@ -1575,7 +1589,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
          * is congested. Allow kswapd to continue until it starts encountering
          * unqueued dirty pages or cycling through the LRU too quickly.
          */
-        if (!sc->hibernation_mode && !current_is_kswapd())
+        if (!sc->hibernation_mode && !current_is_kswapd() &&
+            current_may_throttle())
                 wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
 
         trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,