2 files changed, 30 insertions, 6 deletions

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 1a608877b14e..af48135bd9b8 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -152,14 +152,19 @@ When swap is accounted, following files are added.
 
 usage of mem+swap is limited by memsw.limit_in_bytes.
 
-Note: why 'mem+swap' rather than swap.
+* why 'mem+swap' rather than swap.
 The global LRU(kswapd) can swap out arbitrary pages. Swap-out means
 to move account from memory to swap...there is no change in usage of
-mem+swap.
-
-In other words, when we want to limit the usage of swap without affecting
-global LRU, mem+swap limit is better than just limiting swap from OS point
-of view.
+mem+swap. In other words, when we want to limit the usage of swap without
+affecting global LRU, mem+swap limit is better than just limiting swap from
+OS point of view.
+
+* What happens when a cgroup hits memory.memsw.limit_in_bytes
+When a cgroup his memory.memsw.limit_in_bytes, it's useless to do swap-out
+in this cgroup. Then, swap-out will not be done by cgroup routine and file
+caches are dropped. But as mentioned above, global LRU can do swapout memory
+from it for sanity of the system's memory management state. You can't forbid
+it by cgroup.
 
 2.5 Reclaim
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a83e0395444b..6ceb6f2dbac2 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -177,6 +177,9 @@ struct mem_cgroup {
 
         unsigned int    swappiness;
 
+        /* set when res.limit == memsw.limit */
+        bool            memsw_is_minimum;
+
         /*
          * statistics. This must be placed at the end of memcg.
          */
@@ -847,6 +850,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
         int ret, total = 0;
         int loop = 0;
 
+        /* If memsw_is_minimum==1, swap-out is of-no-use. */
+        if (root_mem->memsw_is_minimum)
+                noswap = true;
+
         while (loop < 2) {
                 victim = mem_cgroup_select_victim(root_mem);
                 if (victim == root_mem)
@@ -1752,6 +1759,12 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                         break;
                 }
                 ret = res_counter_set_limit(&memcg->res, val);
+                if (!ret) {
+                        if (memswlimit == val)
+                                memcg->memsw_is_minimum = true;
+                        else
+                                memcg->memsw_is_minimum = false;
+                }
                 mutex_unlock(&set_limit_mutex);
 
                 if (!ret)
@@ -1799,6 +1812,12 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
                         break;
                 }
                 ret = res_counter_set_limit(&memcg->memsw, val);
+                if (!ret) {
+                        if (memlimit == val)
+                                memcg->memsw_is_minimum = true;
+                        else
+                                memcg->memsw_is_minimum = false;
+                }
                 mutex_unlock(&set_limit_mutex);
 
                 if (!ret)