linux-kernel - Re: FYI: mmap

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Message-Id: <20100708182134.CD3F.A69D9226@jp.fujitsu.com>
Date:	Thu,  8 Jul 2010 18:24:21 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	Michel Lespinasse <walken@...gle.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Divyesh Shah <dpshah@...gle.com>
Subject: Re: FYI: mmap_sem OOM patch

> On Wed, 2010-07-07 at 16:11 -0700, Michel Lespinasse wrote:
> 
> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index f627779..4b3a1c7 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -1062,7 +1062,10 @@ do_page_fault(struct pt_regs *regs, unsigned long error_code)
> >  			bad_area_nosemaphore(regs, error_code, address);
> >  			return;
> >  		}
> > -		down_read(&mm->mmap_sem);
> > +		if (test_thread_flag(TIF_MEMDIE))
> > +			down_read_unfair(&mm->mmap_sem);
> > +		else
> > +			down_read(&mm->mmap_sem);
> >  	} else {
> >  		/*
> >  		 * The above down_read_trylock() might have succeeded in
> 
> I still think adding that _unfair interface is asking for trouble.

Can you please explain trouble that you worry? Why do we need to keep
thread fairness when OOM case?


btw, I also dislike unfair + /proc combination.



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