res_counter: limit change support ebusy

Add an interface to set limit.  This is necessary to memory resource
controller because it shrinks usage at set limit.

Other controllers may not need this interface to shrink usage because
shrinking is not necessary or impossible.

Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index 290205dfe094325a98c77581dea27b3e4a6c69c6..fdeadd9740dc5f99deaa4a8662494914f438e8c4 100644 (file)
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -158,4 +158,20 @@ static inline void res_counter_reset_failcnt(struct res_counter *cnt)
        cnt->failcnt = 0;
        spin_unlock_irqrestore(&cnt->lock, flags);
 }
+
+static inline int res_counter_set_limit(struct res_counter *cnt,
+               unsigned long long limit)
+{
+       unsigned long flags;
+       int ret = -EBUSY;
+
+       spin_lock_irqsave(&cnt->lock, flags);
+       if (cnt->usage < limit) {
+               cnt->limit = limit;
+               ret = 0;
+       }
+       spin_unlock_irqrestore(&cnt->lock, flags);
+       return ret;
+}
+
 #endif