linux-kernel - Re: [PATCH 5/5] x86,mm: make pagefault killable

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Date:	Wed, 23 Mar 2011 16:49:49 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-mm <linux-mm@...ck.org>,
	Andrey Vagin <avagin@...nvz.org>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 5/5] x86,mm: make pagefault killable

On Tue, 22 Mar 2011 20:09:29 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> When oom killer occured, almost processes are getting stuck following
> two points.
> 
> 	1) __alloc_pages_nodemask
> 	2) __lock_page_or_retry
> 
> 1) is not much problematic because TIF_MEMDIE lead to make allocation
> failure and get out from page allocator. 2) is more problematic. When
> OOM situation, Zones typically don't have page cache at all and Memory
> starvation might lead to reduce IO performance largely. When fork bomb
> occur, TIF_MEMDIE task don't die quickly mean fork bomb may create
> new process quickly rather than oom-killer kill it. Then, the system
> may become livelock.
> 
> This patch makes pagefault interruptible by SIGKILL.
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> ---
>  arch/x86/mm/fault.c |    9 +++++++++
>  include/linux/mm.h  |    1 +
>  mm/filemap.c        |   22 +++++++++++++++++-----
>  3 files changed, 27 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 20e3f87..797c7d0 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1035,6 +1035,7 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code)
>  	if (user_mode_vm(regs)) {
>  		local_irq_enable();
>  		error_code |= PF_USER;
> +		flags |= FAULT_FLAG_KILLABLE;
>  	} else {
>  		if (regs->flags & X86_EFLAGS_IF)
>  			local_irq_enable();
> @@ -1138,6 +1139,14 @@ good_area:
>  	}
>  
>  	/*
> +	 * Pagefault was interrupted by SIGKILL. We have no reason to
> +	 * continue pagefault.
> +	 */
> +	if ((flags & FAULT_FLAG_KILLABLE) && (fault & VM_FAULT_RETRY) &&
> +	    fatal_signal_pending(current))
> +		return;
> +

Hmm? up_read(&mm->mmap_sem) ?

Thanks,
-Kame


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