On Thu, Apr 30, 2020 at 6:39 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> 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 ?
>
Seems fine to me. If others are ok with this, please do send a signed-off patch.
> 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
