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>

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index 511f42f..fcb9884 100644 (file)
--- 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 e1338f0..bcdabf3 100644 (file)
--- 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 eb95718..4ad3e6b 100644 (file)
--- 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,