mm: Add transformation message for per-memcg swappiness

The concept of per-memcg swappiness has never landed well in memcg for
cgroup v2. Add a message to users who use it on v1 hierarchy.
Decreased swappiness transforms to memory.swap.max=0 whereas
increased swappiness transforms into active memory.reclaim operation.

Link: https://lore.kernel.org/r/1577252208-32419-1-git-send-email-teawater@gmail.com/
Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
index 286d16fc22ebb70becddb11ed692951b7ccda3cf..02b8206a35941928397331b5071ade62eaa31685 100644 (file)
--- a/Documentation/admin-guide/cgroup-v1/memory.rst
+++ b/Documentation/admin-guide/cgroup-v1/memory.rst
@@ -90,6 +90,7 @@ Brief summary of control files.
                                      used.
  memory.swappiness                  set/show swappiness parameter of vmscan
                                     (See sysctl's vm.swappiness)
+                                    Per memcg knob does not exist in cgroup v2.
  memory.move_charge_at_immigrate     This knob is deprecated.
  memory.oom_control                 set/show oom controls.
                                      This knob is deprecated and shouldn't be

diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index a071fa43d4798a25df7b2bcb76611304ee73d0a4..93291c0e6eac57dc1c5010a4c8e61f2d3e68fa75 100644 (file)
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -1855,9 +1855,11 @@ static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
        if (val > MAX_SWAPPINESS)
                return -EINVAL;
 
-       if (!mem_cgroup_is_root(memcg))
+       if (!mem_cgroup_is_root(memcg)) {
+               pr_info_once("Per memcg swappiness does not exist in cgroup v2. "
+                            "See memory.reclaim or memory.swap.max there\n ")
                WRITE_ONCE(memcg->swappiness, val);
-       else
+       } else
                WRITE_ONCE(vm_swappiness, val);
 
        return 0;