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    Subject[PATCH] memcg: oom: ignore oom warnings from memory.max
    From
    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 <shakeelb@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
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