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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH 5/5] x86,mm: make pagefault killable
Cc: kosaki.motohiro@jp.fujitsu.com, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
        linux-mm <linux-mm@kvack.org>, Andrey Vagin <avagin@openvz.org>,
        Hugh Dickins <hughd@google.com>
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Date: Wed, 23 Mar 2011 17:09:59 +0900 (JST)
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> On Tue, 22 Mar 2011 20:09:29 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@jp.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@jp.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) ?

When __lock_page_or_retry() return 0, It call up_read(mmap_sem) in this
function.

I agree this is strange (or ugly). but I don't want change this spec in
this time.