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    SubjectRe: [PATCH] memcg: oom: ignore oom warnings from memory.max
    On Fri, May 1, 2020 at 2:27 AM Shakeel Butt <shakeelb@google.com> wrote:
    >
    > 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.
    >

    I have been confused by this behavior for several months and I think
    it will confuse more memcg users.
    We should keep the memcg oom behavior consistent with system oom - no
    oom kill if no process.

    What about bellow change ?

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index e28098e13f1c..25fbc37a747f 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -6086,6 +6086,9 @@ static ssize_t memory_max_write(struct
    kernfs_open_file *of,
    continue;
    }

    + if (!cgroup_is_populated(memcg->css.cgroup))
    + break;
    +
    memcg_memory_event(memcg, MEMCG_OOM);
    if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0))
    break;
    > 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
    >
    >


    --
    Thanks
    Yafang

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