This patch adds high/low watermark parameter to res_counter.
and check routine.

splitted out from YAMAMOTO's background page reclaim for memory cgroup set.

TODO?
 - if res_counter's user doesn't want high/low watermark, res_counter_write()
   should ignore low <= high <= limit limitation ?

Changelog
 * added param watermark_state this can ba read without lock lock.


Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
From: YAMAMOTO Takashi <yamamoto@valinux.co.jp>

 include/linux/res_counter.h |   28 ++++++++++++++++++++++++++++
 kernel/res_counter.c        |   42 +++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 69 insertions(+), 1 deletion(-)

Index: linux-2.6.24-rc3-mm2/include/linux/res_counter.h
===================================================================
--- linux-2.6.24-rc3-mm2.orig/include/linux/res_counter.h
+++ linux-2.6.24-rc3-mm2/include/linux/res_counter.h
@@ -19,6 +19,12 @@
  * the helpers described beyond
  */
 
+enum watermark_state {
+	RES_WMARK_BELOW_LOW,
+	RES_WMARK_ABOVE_LOW,
+	RES_WMARK_ABOVE_HIGH,
+};
+
 struct res_counter {
 	/*
 	 * the current resource consumption level
@@ -33,10 +39,17 @@ struct res_counter {
 	 */
 	unsigned long long failcnt;
 	/*
+	 * Watermarks. Must keep low <= high <= limit.
+	 */
+	unsigned long long high_watermark;
+	unsigned long long low_watermark;
+	/*
 	 * the lock to protect all of the above.
 	 * the routines below consider this to be IRQ-safe
 	 */
 	spinlock_t lock;
+	/* can be read without lock */
+	enum watermark_state watermark_state;
 };
 
 /*
@@ -66,6 +79,8 @@ enum {
 	RES_USAGE,
 	RES_LIMIT,
 	RES_FAILCNT,
+	RES_HWMARK,
+	RES_LWMARK,
 };
 
 /*
@@ -124,4 +139,17 @@ static inline bool res_counter_check_und
 	return ret;
 }
 
+/*
+ * Helper function for implementing high/low watermark to resource controller.
+ */
+static inline bool res_counter_below_low_watermark(struct res_counter *cnt)
+{
+	return (cnt->watermark_state == RES_WMARK_BELOW_LOW);
+}
+
+static inline bool res_counter_above_high_watermark(struct res_counter *cnt)
+{
+	return (cnt->watermark_state == RES_WMARK_ABOVE_HIGH);
+}
+
 #endif
Index: linux-2.6.24-rc3-mm2/kernel/res_counter.c
===================================================================
--- linux-2.6.24-rc3-mm2.orig/kernel/res_counter.c
+++ linux-2.6.24-rc3-mm2/kernel/res_counter.c
@@ -17,6 +17,9 @@ void res_counter_init(struct res_counter
 {
 	spin_lock_init(&counter->lock);
 	counter->limit = (unsigned long long)LLONG_MAX;
+	counter->low_watermark = (unsigned long long)LLONG_MAX;
+	counter->high_watermark = (unsigned long long)LLONG_MAX;
+	counter->watermark_state = RES_WMARK_BELOW_LOW;
 }
 
 int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
@@ -27,6 +30,12 @@ int res_counter_charge_locked(struct res
 	}
 
 	counter->usage += val;
+
+	if (counter->usage > counter->high_watermark)
+		counter->watermark_state = RES_WMARK_ABOVE_HIGH;
+	else if (counter->usage > counter->low_watermark)
+		counter->watermark_state = RES_WMARK_ABOVE_LOW;
+
 	return 0;
 }
 
@@ -47,6 +56,11 @@ void res_counter_uncharge_locked(struct 
 		val = counter->usage;
 
 	counter->usage -= val;
+
+	if (counter->usage < counter->low_watermark)
+		counter->watermark_state = RES_WMARK_BELOW_LOW;
+	else if (counter->usage < counter->high_watermark)
+		counter->watermark_state = RES_WMARK_ABOVE_LOW;
 }
 
 void res_counter_uncharge(struct res_counter *counter, unsigned long val)
@@ -69,6 +83,10 @@ res_counter_member(struct res_counter *c
 		return &counter->limit;
 	case RES_FAILCNT:
 		return &counter->failcnt;
+	case RES_HWMARK:
+		return &counter->high_watermark;
+	case RES_LWMARK:
+		return &counter->low_watermark;
 	};
 
 	BUG();
@@ -123,12 +141,34 @@ ssize_t res_counter_write(struct res_cou
 			goto out_free;
 	}
 	spin_lock_irqsave(&counter->lock, flags);
+	/*
+	 * check low <= high <= limit.
+	 */
+	switch (member) {
+		case RES_LIMIT:
+			if (counter->high_watermark > tmp)
+				goto unlock_free;
+			break;
+		case RES_HWMARK:
+			if (tmp < counter->low_watermark ||
+			    tmp > counter->limit)
+				goto unlock_free;
+			break;
+		case RES_LWMARK:
+			if (tmp > counter->high_watermark)
+				goto unlock_free;
+			break;
+		default:
+			break;
+	}
 	val = res_counter_member(counter, member);
 	*val = tmp;
-	spin_unlock_irqrestore(&counter->lock, flags);
 	ret = nbytes;
+unlock_free:
+	spin_unlock_irqrestore(&counter->lock, flags);
 out_free:
 	kfree(buf);
 out:
 	return ret;
 }
+

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