This patch adds high/low watermark parameter to res_counter.
splitted out from YAMAMOTO's background page reclaim for memory cgroup set.

Changes:
 * added param watermark_state this allows status check without lock.


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

 include/linux/res_counter.h |   27 +++++++++++++++++++++++++
 kernel/res_counter.c        |   46 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 72 insertions(+), 1 deletion(-)

Index: linux-2.6.24-rc3-mm1/include/linux/res_counter.h
===================================================================
--- linux-2.6.24-rc3-mm1.orig/include/linux/res_counter.h	2007-11-28 14:33:19.000000000 +0900
+++ linux-2.6.24-rc3-mm1/include/linux/res_counter.h	2007-11-28 16:37:32.000000000 +0900
@@ -19,6 +19,12 @@
  * the helpers described beyond
  */
 
+enum watermark_state {
+	RES_WATERMARK_BELOW_LOW,
+	RES_WATERMARK_ABOVE_LOW,
+	RES_WATERMARK_ABOVE_HIGH,
+};
+
 struct res_counter {
 	/*
 	 * the current resource consumption level
@@ -33,10 +39,19 @@
 	 */
 	unsigned long long failcnt;
 	/*
+	 * Watermarks
+	 * Should be changed automatically when the limit is changed and
+	 * 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;
 };
 
 /*
@@ -73,6 +88,8 @@
 	RES_USAGE,
 	RES_LIMIT,
 	RES_FAILCNT,
+	RES_HIGH_WATERMARK,
+	RES_LOW_WATERMARK,
 };
 
 /*
@@ -131,4 +148,17 @@
 	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_WATERMARK_BELOW_LOW);
+}
+
+static inline bool res_counter_above_high_watermark(struct res_counter *cnt)
+{
+	return (cnt->watermark_state == RES_WATERMARK_ABOVE_HIGH);
+}
+
 #endif
Index: linux-2.6.24-rc3-mm1/kernel/res_counter.c
===================================================================
--- linux-2.6.24-rc3-mm1.orig/kernel/res_counter.c	2007-11-28 14:33:19.000000000 +0900
+++ linux-2.6.24-rc3-mm1/kernel/res_counter.c	2007-11-28 16:33:20.000000000 +0900
@@ -17,6 +17,9 @@
 {
 	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_WATERMARK_BELOW_LOW;
 }
 
 int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
@@ -27,6 +30,15 @@
 	}
 
 	counter->usage += val;
+
+	if (counter->usage > counter->high_watermark) {
+		counter->watermark_state = RES_WATERMARK_ABOVE_HIGH;
+		return 0;
+	}
+
+	if (counter->usage > counter->low_watermark)
+		counter->watermark_state = RES_WATERMARK_ABOVE_LOW;
+
 	return 0;
 }
 
@@ -47,6 +59,13 @@
 		val = counter->usage;
 
 	counter->usage -= val;
+
+	if (counter->usage < counter->low_watermark) {
+		counter->watermark_state = RES_WATERMARK_BELOW_LOW;
+		return;
+	}
+	if (counter->usage < counter->high_watermark)
+		counter->watermark_state = RES_WATERMARK_ABOVE_LOW;
 }
 
 void res_counter_uncharge(struct res_counter *counter, unsigned long val)
@@ -69,6 +88,10 @@
 		return &counter->limit;
 	case RES_FAILCNT:
 		return &counter->failcnt;
+	case RES_HIGH_WATERMARK:
+		return &counter->high_watermark;
+	case RES_LOW_WATERMARK:
+		return &counter->low_watermark;
 	};
 
 	BUG();
@@ -117,7 +140,7 @@
 {
 	int ret;
 	char *buf, *end;
-	unsigned long long flags, tmp, *val;
+	unsigned long long flags, tmp, *val, limit, low, high;
 
 	buf = kmalloc(nbytes + 1, GFP_KERNEL);
 	ret = -ENOMEM;
@@ -141,6 +164,26 @@
 			goto out_free;
 	}
 	spin_lock_irqsave(&counter->lock, flags);
+	/*
+	 * High/Low watermark should be changed automatically AMAP.
+	 */
+	switch (member) {
+		case RES_HIGH_WATERMARK:
+			limit = res_counter_get(counter, RES_LIMIT);
+			if (tmp > limit)
+				goto out_free;
+			low = res_counter_get(counter, RES_LOW_WATERMARK);
+			if (tmp <= low)
+				goto out_free;
+			break;
+		case RES_LOW_WATERMARK:
+			high= res_counter_get(counter, RES_HIGH_WATERMARK);
+			if (tmp >= high)
+				goto out_free;
+			break;
+		default:
+			break;
+	}
 	val = res_counter_member(counter, member);
 	*val = tmp;
 	spin_unlock_irqrestore(&counter->lock, flags);
@@ -150,3 +193,4 @@
 out:
 	return ret;
 }
+

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