Revert "mm: add /proc controls for pdflush threads"

This reverts commit fafd688e.

Work is progressing to switch away from pdflush as the process backing
for flushing out dirty data. So it seems pointless to add more knobs
to control pdflush threads. The original author of the patch did not
have any specific use cases for adding the knobs, so we can easily
revert this before 2.6.30 to avoid having to maintain this API
forever.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

Documentation/sysctl/vm.txt

@@ -39,8 +39,6 @@ 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
@@ -469,32 +467,6 @@ 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.

include/linux/writeback.h

@@ -168,8 +168,6 @@ 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 */

kernel/sysctl.c

@@ -101,7 +101,6 @@ 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_doulongvec_minmax of vm_dirty_bytes */
 static unsigned long dirty_bytes_min = 2 * PAGE_SIZE;
@@ -1033,28 +1032,6 @@ static struct ctl_table vm_table[] = {
 		.mode		= 0444 /* read-only*/,
 		.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",

mm/pdflush.c

@@ -57,14 +57,6 @@ 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
  */
@@ -76,7 +68,7 @@ static unsigned long last_empty_jifs;
  * Thread pool management algorithm:
  * 
  * - The minimum and maximum number of pdflush instances are bound
- *   by nr_pdflush_threads_min and nr_pdflush_threads_max.
+ *   by MIN_PDFLUSH_THREADS and MAX_PDFLUSH_THREADS.
  * 
  * - If there have been no idle pdflush instances for 1 second, create
  *   a new one.
@@ -142,13 +134,14 @@ 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) &&
-			    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);
+			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);
+				}
 			}
 		}
 
@@ -160,7 +153,7 @@ static int __pdflush(struct pdflush_work *my_work)
 		 */
 		if (list_empty(&pdflush_list))
 			continue;
-		if (nr_pdflush_threads <= nr_pdflush_threads_min)
+		if (nr_pdflush_threads <= MIN_PDFLUSH_THREADS)
 			continue;
 		pdf = list_entry(pdflush_list.prev, struct pdflush_work, list);
 		if (time_after(jiffies, pdf->when_i_went_to_sleep + 1 * HZ)) {
@@ -266,9 +259,9 @@ static int __init pdflush_init(void)
 	 * Pre-set nr_pdflush_threads...  If we fail to create,
 	 * the count will be decremented.
 	 */
-	nr_pdflush_threads = nr_pdflush_threads_min;
+	nr_pdflush_threads = MIN_PDFLUSH_THREADS;
 
-	for (i = 0; i < nr_pdflush_threads_min; i++)
+	for (i = 0; i < MIN_PDFLUSH_THREADS; i++)
 		start_one_pdflush_thread();
 	return 0;
 }