vmscan: avoid multiplication overflow in shrink_zone()

[safe/jmp/linux-2.6] / mm / pdflush.c

diff --git a/mm/pdflush.c b/mm/pdflush.c
index 118905e..f2caf96 100644 (file)
--- a/mm/pdflush.c
+++ b/mm/pdflush.c
@@ -58,6 +58,14 @@ static DEFINE_SPINLOCK(pdflush_lock);
 int nr_pdflush_threads = 0;
 
 /*
+ * The max/min number of pdflush threads. R/W by sysctl at
+ * /proc/sys/vm/nr_pdflush_threads_max/min
+ */
+int nr_pdflush_threads_max __read_mostly = MAX_PDFLUSH_THREADS;
+int nr_pdflush_threads_min __read_mostly = MIN_PDFLUSH_THREADS;
+
+
+/*
  * The time at which the pdflush thread pool last went empty
  */
 static unsigned long last_empty_jifs;
@@ -68,7 +76,7 @@ static unsigned long last_empty_jifs;
  * Thread pool management algorithm:
  * 
  * - The minimum and maximum number of pdflush instances are bound
- *   by MIN_PDFLUSH_THREADS and MAX_PDFLUSH_THREADS.
+ *   by nr_pdflush_threads_min and nr_pdflush_threads_max.
  * 
  * - If there have been no idle pdflush instances for 1 second, create
  *   a new one.
@@ -98,7 +106,6 @@ static int __pdflush(struct pdflush_work *my_work)
        INIT_LIST_HEAD(&my_work->list);
 
        spin_lock_irq(&pdflush_lock);
-       nr_pdflush_threads++;
        for ( ; ; ) {
                struct pdflush_work *pdf;
 
@@ -126,20 +133,25 @@ static int __pdflush(struct pdflush_work *my_work)
 
                (*my_work->fn)(my_work->arg0);
 
+               spin_lock_irq(&pdflush_lock);
+
                /*
                 * Thread creation: For how long have there been zero
                 * available threads?
+                *
+                * To throttle creation, we reset last_empty_jifs.
                 */
                if (time_after(jiffies, last_empty_jifs + 1 * HZ)) {
-                       /* unlocked list_empty() test is OK here */
-                       if (list_empty(&pdflush_list)) {
-                               /* unlocked test is OK here */
-                               if (nr_pdflush_threads < MAX_PDFLUSH_THREADS)
-                                       start_one_pdflush_thread();
+                       if (list_empty(&pdflush_list) &&
+                           nr_pdflush_threads < nr_pdflush_threads_max) {
+                               last_empty_jifs = jiffies;
+                               nr_pdflush_threads++;
+                               spin_unlock_irq(&pdflush_lock);
+                               start_one_pdflush_thread();
+                               spin_lock_irq(&pdflush_lock);
                        }
                }
 
-               spin_lock_irq(&pdflush_lock);
                my_work->fn = NULL;
 
                /*
@@ -148,7 +160,7 @@ static int __pdflush(struct pdflush_work *my_work)
                 */
                if (list_empty(&pdflush_list))
                        continue;
-               if (nr_pdflush_threads <= MIN_PDFLUSH_THREADS)
+               if (nr_pdflush_threads <= nr_pdflush_threads_min)
                        continue;
                pdf = list_entry(pdflush_list.prev, struct pdflush_work, list);
                if (time_after(jiffies, pdf->when_i_went_to_sleep + 1 * HZ)) {
@@ -236,14 +248,27 @@ int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0)
 
 static void start_one_pdflush_thread(void)
 {
-       kthread_run(pdflush, NULL, "pdflush");
+       struct task_struct *k;
+
+       k = kthread_run(pdflush, NULL, "pdflush");
+       if (unlikely(IS_ERR(k))) {
+               spin_lock_irq(&pdflush_lock);
+               nr_pdflush_threads--;
+               spin_unlock_irq(&pdflush_lock);
+       }
 }
 
 static int __init pdflush_init(void)
 {
        int i;
 
-       for (i = 0; i < MIN_PDFLUSH_THREADS; i++)
+       /*
+        * Pre-set nr_pdflush_threads...  If we fail to create,
+        * the count will be decremented.
+        */
+       nr_pdflush_threads = nr_pdflush_threads_min;
+
+       for (i = 0; i < nr_pdflush_threads_min; i++)
                start_one_pdflush_thread();
        return 0;
 }