1 files changed, 16 insertions, 1 deletions

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 3148db1296a2..5fdd4e1805e6 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -95,6 +95,8 @@ struct writeback_control {
  * dirtyable memory accordingly.
  */
 struct wb_domain {
+        spinlock_t lock;
+
         /*
          * Scale the writeback cache size proportional to the relative
          * writeout speed.
@@ -115,6 +117,19 @@ struct wb_domain {
         struct fprop_global completions;
         struct timer_list period_timer; /* timer for aging of completions */
         unsigned long period_time;
+
+        /*
+         * The dirtyable memory and dirty threshold could be suddenly
+         * knocked down by a large amount (eg. on the startup of KVM in a
+         * swapless system). This may throw the system into deep dirty
+         * exceeded state and throttle heavy/light dirtiers alike. To
+         * retain good responsiveness, maintain global_dirty_limit for
+         * tracking slowly down to the knocked down dirty threshold.
+         *
+         * Both fields are protected by ->lock.
+         */
+        unsigned long dirty_limit_tstamp;
+        unsigned long dirty_limit;
 };
 
 /*
@@ -153,7 +168,7 @@ void throttle_vm_writeout(gfp_t gfp_mask);
 bool zone_dirty_ok(struct zone *zone);
 int wb_domain_init(struct wb_domain *dom, gfp_t gfp);
 
-extern unsigned long global_dirty_limit;
+extern struct wb_domain global_wb_domain;
 
 /* These are exported to sysctl. */
 extern int dirty_background_ratio;