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>

1 files changed, 20 insertions, 0 deletions

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,