Add high/low watermarks to res_counter.
*This patch itself has no behavior changes to memory resource controller.

Changelog: very old one -> this one (v1)
 - watarmark_state is removed and all state check is done under lock.
 - changed res_counter_charge() interface. The only user is memory
   resource controller. Anyway, returning -ENOMEM here is a bit starnge.
 - Added watermark enable/disable flag for someone don't want watermarks.
 - Restarted against 2.6.25-mm1.
 - some subsystem which doesn't want high-low watermark can work withou it.

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

---
 include/linux/res_counter.h |   41 ++++++++++++++++++++++++---
 kernel/res_counter.c        |   66 ++++++++++++++++++++++++++++++++++++++++----
 mm/memcontrol.c             |    2 -
 3 files changed, 99 insertions(+), 10 deletions(-)

Index: mm-2.6.26-rc2-mm1/include/linux/res_counter.h
===================================================================
--- mm-2.6.26-rc2-mm1.orig/include/linux/res_counter.h
+++ mm-2.6.26-rc2-mm1/include/linux/res_counter.h
@@ -16,6 +16,16 @@
 #include <linux/cgroup.h>
 
 /*
+ * status of resource coutner's usage.
+ */
+enum res_state {
+	RES_BELOW_LOW,	/* usage < lwmark */
+	RES_BELOW_HIGH,	/* lwmark < usage < hwmark */
+	RES_BELOW_LIMIT,	/* hwmark < usage < limit. */
+	RES_OVER_LIMIT,		/* only used at chage. */
+};
+
+/*
  * The core object. the cgroup that wishes to account for some
  * resource may include this counter into its structures and use
  * the helpers described beyond
@@ -39,6 +49,12 @@ struct res_counter {
 	 */
 	unsigned long long failcnt;
 	/*
+	 * watermarks. needs to keep lwmark <= hwmark <= limit.
+	 */
+	unsigned long long hwmark;
+	unsigned long long lwmark;
+	int		   use_watermark;
+	/*
 	 * the lock to protect all of the above.
 	 * the routines below consider this to be IRQ-safe
 	 */
@@ -76,13 +92,18 @@ enum {
 	RES_MAX_USAGE,
 	RES_LIMIT,
 	RES_FAILCNT,
+	RES_HWMARK,
+	RES_LWMARK,
 };
 
 /*
  * helpers for accounting
+ * res_counter_init() ... initialize counter and disable watermarks.
+ * res_counter_init_wmark() ... initialize counter and enable watermarks.
  */
 
 void res_counter_init(struct res_counter *counter);
+void res_counter_init_wmark(struct res_counter *counter);
 
 /*
  * charge - try to consume more resource.
@@ -93,11 +114,21 @@ void res_counter_init(struct res_counter
  *
  * returns 0 on success and <0 if the counter->usage will exceed the
  * counter->limit _locked call expects the counter->lock to be taken
+ * return values:
+ * If watermark is disabled,
+ * RES_BELOW_LIMIT  --  usage is smaller than limt, success.
+ * RES_OVER_LIMIT   --  usage is bigger than limit, failed.
+ *
+ * If watermark is enabled,
+ * RES_BELOW_LOW    -- usage is smaller than low watermark, success
+ * RES_BELOW_HIGH   -- usage is smaller than high watermark, success.
+ * RES_BELOW_LIMIT  -- usage is smaller than limt, success.
+ * RES_OVER_LIMIT   -- usage is bigger than limit, failed.
  */
 
-int __must_check res_counter_charge_locked(struct res_counter *counter,
-		unsigned long val);
-int __must_check res_counter_charge(struct res_counter *counter,
+enum res_state __must_check
+res_counter_charge_locked(struct res_counter *counter, unsigned long val);
+enum res_state __must_check res_counter_charge(struct res_counter *counter,
 		unsigned long val);
 
 /*
@@ -164,4 +195,7 @@ static inline int res_counter_empty(stru
 	spin_unlock_irqrestore(&cnt->lock, flags);
 	return ret;
 }
+
+enum res_state res_counter_state(struct res_counter *counter);
+
 #endif
Index: mm-2.6.26-rc2-mm1/kernel/res_counter.c
===================================================================
--- mm-2.6.26-rc2-mm1.orig/kernel/res_counter.c
+++ mm-2.6.26-rc2-mm1/kernel/res_counter.c
@@ -18,22 +18,40 @@ void res_counter_init(struct res_counter
 {
 	spin_lock_init(&counter->lock);
 	counter->limit = (unsigned long long)LLONG_MAX;
+	counter->use_watermark = 0;
 }
 
-int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
+void res_counter_init_wmark(struct res_counter *counter)
+{
+	spin_lock_init(&counter->lock);
+	counter->limit = (unsigned long long)LLONG_MAX;
+	counter->hwmark = (unsigned long long)LLONG_MAX;
+	counter->lwmark = (unsigned long long)LLONG_MAX;
+	counter->use_watermark = 1;
+}
+
+enum res_state
+res_counter_charge_locked(struct res_counter *counter, unsigned long val)
 {
 	if (counter->usage + val > counter->limit) {
 		counter->failcnt++;
-		return -ENOMEM;
+		return RES_OVER_LIMIT;
 	}
 
 	counter->usage += val;
 	if (counter->usage > counter->max_usage)
 		counter->max_usage = counter->usage;
-	return 0;
+	if (counter->use_watermark) {
+		if (counter->usage <= counter->lwmark)
+			return RES_BELOW_LOW;
+		if (counter->usage <= counter->hwmark)
+			return RES_BELOW_HIGH;
+	}
+	return RES_BELOW_LIMIT;
 }
 
-int res_counter_charge(struct res_counter *counter, unsigned long val)
+enum res_state
+res_counter_charge(struct res_counter *counter, unsigned long val)
 {
 	int ret;
 	unsigned long flags;
@@ -44,6 +62,23 @@ int res_counter_charge(struct res_counte
 	return ret;
 }
 
+enum res_state res_counter_state(struct res_counter *counter)
+{
+	unsigned long flags;
+	enum res_state ret = RES_BELOW_LIMIT;
+
+	spin_lock_irqsave(&counter->lock, flags);
+	if (counter->use_watermark) {
+		if (counter->usage <= counter->lwmark)
+			ret = RES_BELOW_LOW;
+		else if (counter->usage <= counter->hwmark)
+			ret = RES_BELOW_HIGH;
+	}
+	spin_unlock_irqrestore(&counter->lock, flags);
+	return ret;
+}
+
+
 void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
 {
 	if (WARN_ON(counter->usage < val))
@@ -74,6 +109,10 @@ res_counter_member(struct res_counter *c
 		return &counter->limit;
 	case RES_FAILCNT:
 		return &counter->failcnt;
+	case RES_HWMARK:
+		return &counter->hwmark;
+	case RES_LWMARK:
+		return &counter->lwmark;
 	};
 
 	BUG();
@@ -134,10 +173,27 @@ ssize_t res_counter_write(struct res_cou
 			goto out_free;
 	}
 	spin_lock_irqsave(&counter->lock, flags);
+	switch (member) {
+		case RES_LIMIT:
+			if (counter->use_watermark && counter->hwmark > tmp)
+				goto unlock_free;
+			break;
+		case RES_HWMARK:
+			if (tmp < counter->lwmark  || tmp > counter->limit)
+				goto unlock_free;
+			break;
+		case RES_LWMARK:
+			if (tmp > counter->hwmark)
+				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:
Index: mm-2.6.26-rc2-mm1/mm/memcontrol.c
===================================================================
--- mm-2.6.26-rc2-mm1.orig/mm/memcontrol.c
+++ mm-2.6.26-rc2-mm1/mm/memcontrol.c
@@ -559,7 +559,7 @@ static int mem_cgroup_charge_common(stru
 		css_get(&memcg->css);
 	}
 
-	while (res_counter_charge(&mem->res, PAGE_SIZE)) {
+	while (res_counter_charge(&mem->res, PAGE_SIZE) == RES_OVER_LIMIT) {
 		if (!(gfp_mask & __GFP_WAIT))
 			goto out;
 

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