On Mon, 16 Aug 2010 18:15:57 -0700 (PDT)
David Rientjes <rientjes@xxxxxxxxxx> wrote:
> The oom killer's goal is to kill a memory-hogging task so that it may
> exit, free its memory, and allow the current context to allocate the
> memory that triggered it in the first place. Thus, killing a task is
> pointless if other threads sharing its mm cannot be killed because of its
> /proc/pid/oom_adj or /proc/pid/oom_score_adj value.
>
> This patch checks all user threads on the system to determine whether
> oom_badness(p) should return 0 for p, which means it should not be killed.
> If a thread shares p's mm and is unkillable, p is considered to be
> unkillable as well.
>
> Kthreads are not considered toward this rule since they only temporarily
> assume a task's mm via use_mm().
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Thank you. BTW, do you have good idea for speed-up ?
This code seems terribly slow when a system has many processes.
> ---
> v2: change do_each_thread() to for_each_process() as suggested by Oleg.
>
> It's actually not possible to move this logic to oom_kill_task() because
> it's racy: oom_badness() is not a constant score and depends on the state
> of the VM when it is called. This leads to unnecessarily panicking the
> machine in that case as wel as when the same child to sacrifice is
> repeatedly selected in oom_kill_process() based on the parent's badness
> score.
>
> mm/oom_kill.c | 28 +++++++++++++++++++++-------
> 1 files changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -83,6 +83,25 @@ static bool has_intersects_mems_allowed(struct task_struct *tsk,
> #endif /* CONFIG_NUMA */
>
> /*
> + * Determines whether an mm is unfreeable since a user thread attached to
> + * it cannot be killed. Kthreads only temporarily assume a thread's mm,
> + * so they are not considered.
> + *
> + * mm need not be protected by task_lock() since it will not be
> + * dereferened.
> + */
> +static bool is_mm_unfreeable(struct mm_struct *mm)
> +{
> + struct task_struct *p;
> +
> + for_each_process(p)
> + if (p->mm == mm && !(p->flags & PF_KTHREAD) &&
> + p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
> + return true;
> + return false;
> +}
> +
> +/*
> * If this is a system OOM (not a memcg OOM) and the task selected to be
> * killed is not already running at high (RT) priorities, speed up the
> * recovery by boosting the dying task to the lowest FIFO priority.
> @@ -160,12 +179,7 @@ unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
> p = find_lock_task_mm(p);
> if (!p)
> return 0;
> -
> - /*
> - * Shortcut check for OOM_SCORE_ADJ_MIN so the entire heuristic doesn't
> - * need to be executed for something that cannot be killed.
> - */
> - if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
> + if (is_mm_unfreeable(p->mm)) {
> task_unlock(p);
> return 0;
> }
> @@ -675,7 +689,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> read_lock(&tasklist_lock);
> if (sysctl_oom_kill_allocating_task &&
> !oom_unkillable_task(current, NULL, nodemask) &&
> - (current->signal->oom_adj != OOM_DISABLE)) {
> + !is_mm_unfreeable(current->mm)) {
> /*
> * oom_kill_process() needs tasklist_lock held. If it returns
> * non-zero, current could not be killed so we must fallback to
>
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