linux-kernel - Re: [PATCH] oom: Make coredump interruptible

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Message-ID: <20100604112721.GA12582@redhat.com>
Date:	Fri, 4 Jun 2010 13:27:21 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Roland McGrath <roland@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH] oom: Make coredump interruptible

On 06/04, KOSAKI Motohiro wrote:
>
> > ... to set TIF_MEMDIE which should be checked in elf_core_dump().
> >
> > Probably yes.
>
> Yep, probably. but can you please allow me additonal explanation?
>
> In multi threaded OOM case, we have two problematic routine, coredump
> and vmscan. Roland's idea can only solve the former.
>
> But I also interest vmscan quickly exit if OOM received.

Yes, agreed. See another email from me, MMF_ flags looks "obviously
useful" to me.

(I'd suggest you to add a note into the changelog, to explain
 that the new flag makes sense even without coredump problems).

> @@ -410,6 +409,8 @@ static int __oom_kill_process(struct task_struct *p, struct mem_cgroup *mem,
>  	 */
>  	p->rt.time_slice = HZ;
>  	set_tsk_thread_flag(p, TIF_MEMDIE);
> +	set_bit(MMF_OOM_KILLED, &p->mm->flags);
> +	task_unlock(p);

IIUC, it has find_lock_task() mm above and thus we can trust p->mm ?
(I am asking just in case, I lost the plot a bit).

Ack or Reviewed, whatever your prefer.

Very minor nit.

> @@ -2038,6 +2038,10 @@ static int elf_core_dump(struct coredump_params *cprm)
>                               page_cache_release(page);
>                       } else
>                               stop = !dump_seek(cprm->file, PAGE_SIZE);
> +
> +                     /* The task need to exit ASAP if received OOM. */
> +                     if (test_bit(MMF_OOM_KILLED, &current->mm->flags))
> +                             stop = 1;

Perhaps this check makes more sense at the start of the loop,
and there is no need to set "stop = 1" (this var is not visible
outside of "for (;;) {}" anyway). Cosmetic, up to you.

Oleg.

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