linux-kernel - Re: FYI: mmap

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Date:	Thu,  8 Jul 2010 18:51:20 +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 Thu, 2010-07-08 at 18:24 +0900, KOSAKI Motohiro wrote:
> > > 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?
> 
> Just the whole concept of the unfair thing offends me ;-) I didn't
> really look at the particular application in this case.

I see. 
Yup, I agree unfair thing concept is a bit ugly. If anyone have 
alternative idea, I agree to choose that thing.



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