Messages in this thread | | | Date | Wed, 11 Sep 2013 19:06:05 +0400 | From | Sergey Dyasly <> | Subject | Re: [PATCH] OOM killer: wait for tasks with pending SIGKILL to exit |
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On Mon, 9 Sep 2013 13:07:08 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:
> > /* > > * If this task is not being ptraced on exit, then wait for it > > * to finish before killing some other task unnecessarily. > > */ > > - if (!(task->group_leader->ptrace & PT_TRACE_EXIT)) > > + if (!(task->group_leader->ptrace & PT_TRACE_EXIT)) { > > + set_tsk_thread_flag(task, TIF_MEMDIE); > > This does not, we do not give access to memory reserves unless the process > needs it to allocate memory. The task here, which is not current, can > call into the oom killer and be granted memory reserves if necessary.
True. However, why TIF_MEMDIE is set for PF_EXITING task in oom_kill_process() then? Also, setting TIF_MEMDIE will avoid direct reclaim and memory allocation should be fast if exiting task needs it.
> > @@ -412,16 +415,6 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, > > static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL, > > DEFAULT_RATELIMIT_BURST); > > > > - /* > > - * If the task is already exiting, don't alarm the sysadmin or kill > > - * its children or threads, just set TIF_MEMDIE so it can die quickly > > - */ > > - if (p->flags & PF_EXITING) { > > - set_tsk_thread_flag(p, TIF_MEMDIE); > > - put_task_struct(p); > > - return; > > - } > > I think you misunderstood the point of this; if a selected process is > already in the exit path then this is simply avoiding dumping oom kill > lines to the kernel log. We want to keep doing that.
This happens in oom_kill_process() after victim has been selected by select_bad_process(). But there is already PF_EXITING check in oom_scan_process_thread() and in this case OOM code won't call oom_kill_process. There is only a slight chance that victim will become PF_EXITING between scan and kill.
The only difference is in force_kill flag, and the only case where it's set is SysRq. And I think in this case OOM killer messages are a good thing to have even when victim is already exiting, instead of just silence.
-- Sergey Dyasly <dserrg@gmail.com>
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