Re: [PATCH] mm/oom_kill: add sysctl_oom_dump_stack to control kernel stack dumping on OOM

[Michal Hocko <mhocko@suse.com>]

On Fri 12-12-25 04:24:33, Yang Xin wrote:
>     Most OOM kills triggered by user-space processes produce kernel stack
>     traces that are not helpful for diagnosing the root cause. These traces
>     usually just show the page fault handler or system call entry.
> 
>     Furthermore, dump_stack() can be expensive. It often runs with
>     interrupts disabled or holds the console lock for a long time,
>     potentially causing system latencies and preventing the system from
>     responding to other events.
> 
>     This patch adds a new sysctl vm.oom_dump_stack to control this
>     behavior. Writing '0' to /proc/sys/vm/oom_dump_stack suppresses the
>     kernel stack dump during OOM kills, while '1' (the default) preserves
>     the existing behavior.

While I fundamentally do not object to ways to suppress stacks traces
for OOM I would really like to hear more what kind of overhead we are
talking about here (stack traces are reported for tracing and other low
latency situations) and why does this matter for as cold of a path as
OOM is.

Also we are getting way too many of these sysctls. Maybe it is time to
look for a more customizable way to configure oom output that doesn't
require sysctl per output feature.

> Signed-off-by: Yang Xin <redleaf@linux.alibaba.com>
> ---
>  mm/oom_kill.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 5eb11fbba704..a51dbd2e6912 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -56,6 +56,7 @@
>  static int sysctl_panic_on_oom;
>  static int sysctl_oom_kill_allocating_task;
>  static int sysctl_oom_dump_tasks = 1;
> +static int sysctl_oom_dump_stack = 1;
>  
>  /*
>   * Serializes oom killer invocations (out_of_memory()) from all contexts to
> @@ -464,7 +465,9 @@ static void dump_header(struct oom_control *oc)
>  	if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
>  		pr_warn("COMPACTION is disabled!!!\n");
>  
> -	dump_stack();
> +	if (sysctl_oom_dump_stack)
> +		dump_stack();
> +
>  	if (is_memcg_oom(oc))
>  		mem_cgroup_print_oom_meminfo(oc->memcg);
>  	else {
> @@ -736,6 +739,13 @@ static const struct ctl_table vm_oom_kill_table[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec,
>  	},
> +	{
> +                .procname       = "oom_dump_stack",
> +                .data           = &sysctl_oom_dump_stack,
> +                .maxlen         = sizeof(sysctl_oom_dump_stack),
> +                .mode           = 0644,
> +                .proc_handler   = proc_dointvec,
> +        },
>  };
>  #endif
>  
> -- 
> 2.30.2
> 

-- 
Michal Hocko
SUSE Labs