4 files changed, 72 insertions, 12 deletions

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 3197fc83bc51..97c4b3284329 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -39,6 +39,8 @@ Currently, these files are in /proc/sys/vm:
 - nr_hugepages
 - nr_overcommit_hugepages
 - nr_pdflush_threads
+- nr_pdflush_threads_min
+- nr_pdflush_threads_max
 - nr_trim_pages         (only if CONFIG_MMU=n)
 - numa_zonelist_order
 - oom_dump_tasks
@@ -463,6 +465,32 @@ The default value is 0.
 
 ==============================================================
 
+nr_pdflush_threads_min
+
+This value controls the minimum number of pdflush threads.
+
+At boot time, the kernel will create and maintain 'nr_pdflush_threads_min'
+threads for the kernel's lifetime.
+
+The default value is 2.  The minimum value you can specify is 1, and
+the maximum value is the current setting of 'nr_pdflush_threads_max'.
+
+See 'nr_pdflush_threads_max' below for more information.
+
+==============================================================
+
+nr_pdflush_threads_max
+
+This value controls the maximum number of pdflush threads that can be
+created.  The pdflush algorithm will create a new pdflush thread (up to
+this maximum) if no pdflush threads have been available for >= 1 second.
+
+The default value is 8.  The minimum value you can specify is the
+current value of 'nr_pdflush_threads_min' and the
+maximum is 1000.
+
+==============================================================
+
 overcommit_memory:
 
 This value contains a flag that enables memory overcommitment.
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 93445477f86a..9c1ed1fb6ddb 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -168,6 +168,8 @@ void writeback_set_ratelimit(void);
 /* pdflush.c */
 extern int nr_pdflush_threads;  /* Global so it can be exported to sysctl
                                    read-only. */
+extern int nr_pdflush_threads_max; /* Global so it can be exported to sysctl */
+extern int nr_pdflush_threads_min; /* Global so it can be exported to sysctl */
 
 
 #endif          /* WRITEBACK_H */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index b125e3387568..72eb1a41dcab 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -101,6 +101,7 @@ static int __maybe_unused one = 1;
 static int __maybe_unused two = 2;
 static unsigned long one_ul = 1;
 static int one_hundred = 100;
+static int one_thousand = 1000;
 
 /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
 static int maxolduid = 65535;
@@ -1027,6 +1028,28 @@ static struct ctl_table vm_table[] = {
                 .proc_handler   = &proc_dointvec,
         },
         {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "nr_pdflush_threads_min",
+                .data           = &nr_pdflush_threads_min,
+                .maxlen         = sizeof nr_pdflush_threads_min,
+                .mode           = 0644 /* read-write */,
+                .proc_handler   = &proc_dointvec_minmax,
+                .strategy       = &sysctl_intvec,
+                .extra1         = &one,
+                .extra2         = &nr_pdflush_threads_max,
+        },
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "nr_pdflush_threads_max",
+                .data           = &nr_pdflush_threads_max,
+                .maxlen         = sizeof nr_pdflush_threads_max,
+                .mode           = 0644 /* read-write */,
+                .proc_handler   = &proc_dointvec_minmax,
+                .strategy       = &sysctl_intvec,
+                .extra1         = &nr_pdflush_threads_min,
+                .extra2         = &one_thousand,
+        },
+        {
                 .ctl_name       = VM_SWAPPINESS,
                 .procname       = "swappiness",
                 .data           = &vm_swappiness,
diff --git a/mm/pdflush.c b/mm/pdflush.c
index 235ac440c44e..f2caf96993f8 100644
--- 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.
@@ -134,14 +142,13 @@ static int __pdflush(struct pdflush_work *my_work)
                  * To throttle creation, we reset last_empty_jifs.
                  */
                 if (time_after(jiffies, last_empty_jifs + 1 * HZ)) {
-                        if (list_empty(&pdflush_list)) {
-                                if (nr_pdflush_threads < MAX_PDFLUSH_THREADS) {
-                                        last_empty_jifs = jiffies;
-                                        nr_pdflush_threads++;
-                                        spin_unlock_irq(&pdflush_lock);
-                                        start_one_pdflush_thread();
-                                        spin_lock_irq(&pdflush_lock);
-                                }
+                        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);
                         }
                 }
 
@@ -153,7 +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)) {
@@ -259,9 +266,9 @@ static int __init pdflush_init(void)
          * Pre-set nr_pdflush_threads...  If we fail to create,
          * the count will be decremented.
          */
-        nr_pdflush_threads = MIN_PDFLUSH_THREADS;
+        nr_pdflush_threads = nr_pdflush_threads_min;
 
-        for (i = 0; i < MIN_PDFLUSH_THREADS; i++)
+        for (i = 0; i < nr_pdflush_threads_min; i++)
                 start_one_pdflush_thread();
         return 0;
 }