memory controller: soft limit interface

Add an interface to allow get/set of soft limits.  Soft limits for memory
plus swap controller (memsw) is currently not supported.  Resource
counters have been enhanced to support soft limits and new type
RES_SOFT_LIMIT has been added.  Unlike hard limits, soft limits can be
directly set and do not need any reclaim or checks before setting them to
a newer value.

Kamezawa-San raised a question as to whether soft limit should belong to
res_counter.  Since all resources understand the basic concepts of hard
and soft limits, it is justified to add soft limits here.  Soft limits are
a generic resource usage feature, even file system quotas support soft
limits.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 81 insertions, 0 deletions

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index 511f42fc6816..fcb9884df618 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -35,6 +35,10 @@ struct res_counter {
          */
         unsigned long long limit;
         /*
+         * the limit that usage can be exceed
+         */
+        unsigned long long soft_limit;
+        /*
          * the number of unsuccessful attempts to consume the resource
          */
         unsigned long long failcnt;
@@ -87,6 +91,7 @@ enum {
         RES_MAX_USAGE,
         RES_LIMIT,
         RES_FAILCNT,
+        RES_SOFT_LIMIT,
 };
 
 /*
@@ -132,6 +137,36 @@ static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
         return false;
 }
 
+static inline bool res_counter_soft_limit_check_locked(struct res_counter *cnt)
+{
+        if (cnt->usage < cnt->soft_limit)
+                return true;
+
+        return false;
+}
+
+/**
+ * Get the difference between the usage and the soft limit
+ * @cnt: The counter
+ *
+ * Returns 0 if usage is less than or equal to soft limit
+ * The difference between usage and soft limit, otherwise.
+ */
+static inline unsigned long long
+res_counter_soft_limit_excess(struct res_counter *cnt)
+{
+        unsigned long long excess;
+        unsigned long flags;
+
+        spin_lock_irqsave(&cnt->lock, flags);
+        if (cnt->usage <= cnt->soft_limit)
+                excess = 0;
+        else
+                excess = cnt->usage - cnt->soft_limit;
+        spin_unlock_irqrestore(&cnt->lock, flags);
+        return excess;
+}
+
 /*
  * Helper function to detect if the cgroup is within it's limit or
  * not. It's currently called from cgroup_rss_prepare()
@@ -147,6 +182,17 @@ static inline bool res_counter_check_under_limit(struct res_counter *cnt)
         return ret;
 }
 
+static inline bool res_counter_check_under_soft_limit(struct res_counter *cnt)
+{
+        bool ret;
+        unsigned long flags;
+
+        spin_lock_irqsave(&cnt->lock, flags);
+        ret = res_counter_soft_limit_check_locked(cnt);
+        spin_unlock_irqrestore(&cnt->lock, flags);
+        return ret;
+}
+
 static inline void res_counter_reset_max(struct res_counter *cnt)
 {
         unsigned long flags;
@@ -180,4 +226,16 @@ static inline int res_counter_set_limit(struct res_counter *cnt,
         return ret;
 }
 
+static inline int
+res_counter_set_soft_limit(struct res_counter *cnt,
+                                unsigned long long soft_limit)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&cnt->lock, flags);
+        cnt->soft_limit = soft_limit;
+        spin_unlock_irqrestore(&cnt->lock, flags);
+        return 0;
+}
+
 #endif
diff --git a/kernel/res_counter.c b/kernel/res_counter.c
index e1338f074314..bcdabf37c40b 100644
--- a/kernel/res_counter.c
+++ b/kernel/res_counter.c
@@ -19,6 +19,7 @@ void res_counter_init(struct res_counter *counter, struct res_counter *parent)
 {
         spin_lock_init(&counter->lock);
         counter->limit = RESOURCE_MAX;
+        counter->soft_limit = RESOURCE_MAX;
         counter->parent = parent;
 }
 
@@ -101,6 +102,8 @@ res_counter_member(struct res_counter *counter, int member)
                 return &counter->limit;
         case RES_FAILCNT:
                 return &counter->failcnt;
+        case RES_SOFT_LIMIT:
+                return &counter->soft_limit;
         };
 
         BUG();
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index eb9571815f0c..4ad3e6be045d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2123,6 +2123,20 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
                 else
                         ret = mem_cgroup_resize_memsw_limit(memcg, val);
                 break;
+        case RES_SOFT_LIMIT:
+                ret = res_counter_memparse_write_strategy(buffer, &val);
+                if (ret)
+                        break;
+                /*
+                 * For memsw, soft limits are hard to implement in terms
+                 * of semantics, for now, we support soft limits for
+                 * control without swap
+                 */
+                if (type == _MEM)
+                        ret = res_counter_set_soft_limit(&memcg->res, val);
+                else
+                        ret = -EINVAL;
+                break;
         default:
                 ret = -EINVAL; /* should be BUG() ? */
                 break;
@@ -2376,6 +2390,12 @@ static struct cftype mem_cgroup_files[] = {
                 .read_u64 = mem_cgroup_read,
         },
         {
+                .name = "soft_limit_in_bytes",
+                .private = MEMFILE_PRIVATE(_MEM, RES_SOFT_LIMIT),
+                .write_string = mem_cgroup_write,
+                .read_u64 = mem_cgroup_read,
+        },
+        {
                 .name = "failcnt",
                 .private = MEMFILE_PRIVATE(_MEM, RES_FAILCNT),
                 .trigger = mem_cgroup_reset,