Re: FYI: mmap_sem OOM patch

[Peter Zijlstra <peterz@infradead.org>]

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.


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