1 files changed, 137 insertions, 1 deletions

diff --git a/kernel/slow-work.c b/kernel/slow-work.c
index 5a7392734c82..454abb21c8bd 100644
--- a/kernel/slow-work.c
+++ b/kernel/slow-work.c
@@ -16,6 +16,14 @@
 #include <linux/wait.h>
 #include <asm/system.h>
 
+#define SLOW_WORK_CULL_TIMEOUT (5 * HZ) /* cull threads 5s after running out of
+                                         * things to do */
+#define SLOW_WORK_OOM_TIMEOUT (5 * HZ)  /* can't start new threads for 5s after
+                                         * OOM */
+
+static void slow_work_cull_timeout(unsigned long);
+static void slow_work_oom_timeout(unsigned long);
+
 /*
  * The pool of threads has at least min threads in it as long as someone is
  * using the facility, and may have as many as max.
@@ -29,6 +37,12 @@ static unsigned vslow_work_proportion = 50; /* % of threads that may process
 static atomic_t slow_work_thread_count;
 static atomic_t vslow_work_executing_count;
 
+static bool slow_work_may_not_start_new_thread;
+static bool slow_work_cull; /* cull a thread due to lack of activity */
+static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);
+static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
+static struct slow_work slow_work_new_thread; /* new thread starter */
+
 /*
  * The queues of work items and the lock governing access to them.  These are
  * shared between all the CPUs.  It doesn't make sense to have per-CPU queues
@@ -89,6 +103,14 @@ static bool slow_work_execute(void)
 
         vsmax = slow_work_calc_vsmax();
 
+        /* see if we can schedule a new thread to be started if we're not
+         * keeping up with the work */
+        if (!waitqueue_active(&slow_work_thread_wq) &&
+            (!list_empty(&slow_work_queue) || !list_empty(&vslow_work_queue)) &&
+            atomic_read(&slow_work_thread_count) < slow_work_max_threads &&
+            !slow_work_may_not_start_new_thread)
+                slow_work_enqueue(&slow_work_new_thread);
+
         /* find something to execute */
         spin_lock_irq(&slow_work_queue_lock);
         if (!list_empty(&vslow_work_queue) &&
@@ -243,6 +265,33 @@ cant_get_ref:
 EXPORT_SYMBOL(slow_work_enqueue);
 
 /*
+ * Worker thread culling algorithm
+ */
+static bool slow_work_cull_thread(void)
+{
+        unsigned long flags;
+        bool do_cull = false;
+
+        spin_lock_irqsave(&slow_work_queue_lock, flags);
+
+        if (slow_work_cull) {
+                slow_work_cull = false;
+
+                if (list_empty(&slow_work_queue) &&
+                    list_empty(&vslow_work_queue) &&
+                    atomic_read(&slow_work_thread_count) >
+                    slow_work_min_threads) {
+                        mod_timer(&slow_work_cull_timer,
+                                  jiffies + SLOW_WORK_CULL_TIMEOUT);
+                        do_cull = true;
+                }
+        }
+
+        spin_unlock_irqrestore(&slow_work_queue_lock, flags);
+        return do_cull;
+}
+
+/*
  * Determine if there is slow work available for dispatch
  */
 static inline bool slow_work_available(int vsmax)
@@ -273,7 +322,8 @@ static int slow_work_thread(void *_data)
                                 TASK_INTERRUPTIBLE);
                 if (!freezing(current) &&
                     !slow_work_threads_should_exit &&
-                    !slow_work_available(vsmax))
+                    !slow_work_available(vsmax) &&
+                    !slow_work_cull)
                         schedule();
                 finish_wait(&slow_work_thread_wq, &wait);
 
@@ -285,11 +335,20 @@ static int slow_work_thread(void *_data)
 
                 if (slow_work_available(vsmax) && slow_work_execute()) {
                         cond_resched();
+                        if (list_empty(&slow_work_queue) &&
+                            list_empty(&vslow_work_queue) &&
+                            atomic_read(&slow_work_thread_count) >
+                            slow_work_min_threads)
+                                mod_timer(&slow_work_cull_timer,
+                                          jiffies + SLOW_WORK_CULL_TIMEOUT);
                         continue;
                 }
 
                 if (slow_work_threads_should_exit)
                         break;
+
+                if (slow_work_cull && slow_work_cull_thread())
+                        break;
         }
 
         if (atomic_dec_and_test(&slow_work_thread_count))
@@ -297,6 +356,77 @@ static int slow_work_thread(void *_data)
         return 0;
 }
 
+/*
+ * Handle thread cull timer expiration
+ */
+static void slow_work_cull_timeout(unsigned long data)
+{
+        slow_work_cull = true;
+        wake_up(&slow_work_thread_wq);
+}
+
+/*
+ * Get a reference on slow work thread starter
+ */
+static int slow_work_new_thread_get_ref(struct slow_work *work)
+{
+        return 0;
+}
+
+/*
+ * Drop a reference on slow work thread starter
+ */
+static void slow_work_new_thread_put_ref(struct slow_work *work)
+{
+}
+
+/*
+ * Start a new slow work thread
+ */
+static void slow_work_new_thread_execute(struct slow_work *work)
+{
+        struct task_struct *p;
+
+        if (slow_work_threads_should_exit)
+                return;
+
+        if (atomic_read(&slow_work_thread_count) >= slow_work_max_threads)
+                return;
+
+        if (!mutex_trylock(&slow_work_user_lock))
+                return;
+
+        slow_work_may_not_start_new_thread = true;
+        atomic_inc(&slow_work_thread_count);
+        p = kthread_run(slow_work_thread, NULL, "kslowd");
+        if (IS_ERR(p)) {
+                printk(KERN_DEBUG "Slow work thread pool: OOM\n");
+                if (atomic_dec_and_test(&slow_work_thread_count))
+                        BUG(); /* we're running on a slow work thread... */
+                mod_timer(&slow_work_oom_timer,
+                          jiffies + SLOW_WORK_OOM_TIMEOUT);
+        } else {
+                /* ratelimit the starting of new threads */
+                mod_timer(&slow_work_oom_timer, jiffies + 1);
+        }
+
+        mutex_unlock(&slow_work_user_lock);
+}
+
+static const struct slow_work_ops slow_work_new_thread_ops = {
+        .get_ref        = slow_work_new_thread_get_ref,
+        .put_ref        = slow_work_new_thread_put_ref,
+        .execute        = slow_work_new_thread_execute,
+};
+
+/*
+ * post-OOM new thread start suppression expiration
+ */
+static void slow_work_oom_timeout(unsigned long data)
+{
+        slow_work_may_not_start_new_thread = false;
+}
+
 /**
  * slow_work_register_user - Register a user of the facility
  *
@@ -316,6 +446,10 @@ int slow_work_register_user(void)
                 init_completion(&slow_work_last_thread_exited);
 
                 slow_work_threads_should_exit = false;
+                slow_work_init(&slow_work_new_thread,
+                               &slow_work_new_thread_ops);
+                slow_work_may_not_start_new_thread = false;
+                slow_work_cull = false;
 
                 /* start the minimum number of threads */
                 for (loop = 0; loop < slow_work_min_threads; loop++) {
@@ -369,6 +503,8 @@ void slow_work_unregister_user(void)
                        " Shut down complete\n");
         }
 
+        del_timer_sync(&slow_work_cull_timer);
+
         mutex_unlock(&slow_work_user_lock);
 }
 EXPORT_SYMBOL(slow_work_unregister_user);