linux-kernel - Re: [PATCH] oom: OOM-Killed process don't invoke pagefault-oom

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Date:	Fri, 15 Jan 2010 00:02:57 +1100
From:	Nick Piggin <npiggin@...e.de>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Jeff Dike <jdike@...toit.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] oom: OOM-Killed process don't invoke pagefault-oom

Hi,

I don't think this should be required, because the oom killer does not
kill a new task if there is already one in memdie state.

If you have any further tweaks to the heuristic (such as a fatal signal
pending), then it should probably go in select_bad_process() or
somewhere like that.

Thanks,
Nick

On Thu, Jan 14, 2010 at 07:22:34PM +0900, KOSAKI Motohiro wrote:
> 
> Nick, I've found this issue by code review. I'm glad if you review this
> patch.
> 
> Thanks.
> 
> =============================
> commit 1c0fe6e3 (invoke oom-killer from page fault) created
> page fault specific oom handler.
> 
> But If OOM occur, alloc_pages() in page fault might return
> NULL. It mean page fault return VM_FAULT_OOM. But OOM Killer
> itself sholdn't invoke next OOM Kill. it is obviously strange.
> 
> Plus, process exiting itself makes some free memory. we
> don't need kill another process.
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Cc: Nick Piggin <npiggin@...e.de>
> Cc: Jeff Dike <jdike@...toit.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  mm/oom_kill.c |    9 +++++++++
>  1 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 4f167b8..86cecdf 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -596,6 +596,15 @@ void pagefault_out_of_memory(void)
>  {
>  	unsigned long freed = 0;
>  
> +	/*
> +	 * If the task was received SIGKILL while memory allocation, alloc_pages
> +	 * might return NULL and it cause page fault return VM_FAULT_OOM. But
> +	 * in such case, the task don't need kill any another task, it need
> +	 * just die.
> +	 */
> +	if (fatal_signal_pending(current))
> +		return;
> +
>  	blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
>  	if (freed > 0)
>  		/* Got some memory back in the last second. */
> -- 
> 1.6.5.2
> 
> 
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