Re: [patch] memcg: give current access to memory reserves if it's trying to die

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 9 Mar 2011 13:27:50 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> When a memcg is oom and current has already received a SIGKILL, then give
> it access to memory reserves with a higher scheduling priority so that it
> may quickly exit and free its memory.
> 
> This is identical to the global oom killer and is done even before
> checking for panic_on_oom: a pending SIGKILL here while panic_on_oom is
> selected is guaranteed to have come from userspace; the thread only needs
> access to memory reserves to exit and thus we don't unnecessarily panic
> the machine until the kernel has no last resort to free memory.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  mm/oom_kill.c |   11 +++++++++++
>  1 files changed, 11 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -537,6 +537,17 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
>  	unsigned int points = 0;
>  	struct task_struct *p;
>  
> +	/*
> +	 * If current has a pending SIGKILL, then automatically select it.  The
> +	 * goal is to allow it to allocate so that it may quickly exit and free
> +	 * its memory.
> +	 */
> +	if (fatal_signal_pending(current)) {
> +		set_thread_flag(TIF_MEMDIE);
> +		boost_dying_task_prio(current, NULL);
> +		return;
> +	}
> +
>  	check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, 0, NULL);
>  	limit = mem_cgroup_get_limit(mem) >> PAGE_SHIFT;
>  	read_lock(&tasklist_lock);

The code duplication seems a bit gratuitous.



Was it deliberate that mem_cgroup_out_of_memory() ignores the oom
notifier callbacks?

(Why does that notifier list exist at all?  Wouldn't it be better to do
this via a vmscan shrinker?  Perhaps altered to be passed the scanning
priority?)

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