On Fri, May 1, 2020 at 2:27 AM Shakeel Butt <shakeelb@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
> 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
