[PATCH] memcg: oom: ignore oom warnings from memory.max

[Shakeel Butt]

Lowering memory.max can trigger an oom-kill if the reclaim does not
succeed. However if oom-killer does not find a process for killing, it
dumps a lot of warnings.

Deleting a memcg does not reclaim memory from it and the memory can
linger till there is a memory pressure. One normal way to proactively
reclaim such memory is to set memory.max to 0 just before deleting the
memcg. However if some of the memcg's memory is pinned by others, this
operation can trigger an oom-kill without any process and thus can log a
lot un-needed warnings. So, ignore all such warnings from memory.max.

Signed-off-by: Shakeel Butt <shake...@google.com>
---
 include/linux/oom.h | 3 +++
 mm/memcontrol.c     | 9 +++++----
 mm/oom_kill.c       | 2 +-
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/oom.h b/include/linux/oom.h
index c696c265f019..6345dc55df64 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -52,6 +52,9 @@ struct oom_control {
 
        /* Used to print the constraint info. */
        enum oom_constraint constraint;
+
+       /* Do not warn even if there is no process to be killed. */
+       bool no_warn;
 };
 
 extern struct mutex oom_lock;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 317dbbaac603..a1f00d9b9bb0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1571,7 +1571,7 @@ unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
 }
 
 static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
-                                    int order)
+                                    int order, bool no_warn)
 {
        struct oom_control oc = {
                .zonelist = NULL,
@@ -1579,6 +1579,7 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup 
*memcg, gfp_t gfp_mask,
                .memcg = memcg,
                .gfp_mask = gfp_mask,
                .order = order,
+               .no_warn = no_warn,
        };
        bool ret;
 
@@ -1821,7 +1822,7 @@ static enum oom_status mem_cgroup_oom(struct mem_cgroup 
*memcg, gfp_t mask, int
                mem_cgroup_oom_notify(memcg);
 
        mem_cgroup_unmark_under_oom(memcg);
-       if (mem_cgroup_out_of_memory(memcg, mask, order))
+       if (mem_cgroup_out_of_memory(memcg, mask, order, false))
                ret = OOM_SUCCESS;
        else
                ret = OOM_FAILED;
@@ -1880,7 +1881,7 @@ bool mem_cgroup_oom_synchronize(bool handle)
                mem_cgroup_unmark_under_oom(memcg);
                finish_wait(&memcg_oom_waitq, &owait.wait);
                mem_cgroup_out_of_memory(memcg, current->memcg_oom_gfp_mask,
-                                        current->memcg_oom_order);
+                                        current->memcg_oom_order, false);
        } else {
                schedule();
                mem_cgroup_unmark_under_oom(memcg);
@@ -6106,7 +6107,7 @@ static ssize_t memory_max_write(struct kernfs_open_file 
*of,
                }
 
                memcg_memory_event(memcg, MEMCG_OOM);
-               if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0))
+               if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0, true))
                        break;
        }
 
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 463b3d74a64a..5ace39f6fe1e 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -1098,7 +1098,7 @@ bool out_of_memory(struct oom_control *oc)
 
        select_bad_process(oc);
        /* Found nothing?!?! */
-       if (!oc->chosen) {
+       if (!oc->chosen && !oc->no_warn) {
                dump_header(oc, NULL);
                pr_warn("Out of memory and no killable processes...\n");
                /*
-- 
2.26.2.526.g744177e7f7-goog