linux-kernel - Re: [PATCH v3][RFC] add MAP

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Message-ID: <20091008091611.GD16702@redhat.com>
Date:	Thu, 8 Oct 2009 11:16:12 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	WANG Cong <xiyou.wangcong@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v3][RFC] add MAP_UNLOCKED mmap flag

On Thu, Oct 08, 2009 at 05:10:35PM +0800, WANG Cong wrote:
> Gleb Natapov <gleb@...hat.com> writes:
> 
> > If application does mlockall(MCL_FUTURE) it is no longer possible to
> > mmap file bigger than main memory or allocate big area of anonymous
> > memory. Sometimes it is desirable to lock everything related to program
> > execution into memory, but still be able to mmap big file or allocate
> > huge amount of memory and allow OS to swap them on demand. MAP_UNLOCKED
> > allows to do that.
> >
> > Signed-off-by: Gleb Natapov <gleb@...hat.com>
> 
> <snip>
> 
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 73f5e4b..ecc4471 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -985,6 +985,9 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
> >  		if (!can_do_mlock())
> >  			return -EPERM;
> >  
> > +        if (flags & MAP_UNLOCKED)
> > +                vm_flags &= ~VM_LOCKED;
> > +
> >  	/* mlock MCL_FUTURE? */
> >  	if (vm_flags & VM_LOCKED) {
> >  		unsigned long locked, lock_limit;
> 
> So, if I read it correctly, it is perfectly legal to set
> both MAP_LOCKED and MAP_UNLOCKED at the same time? While
> the behavior is still same as only setting MAP_UNLOCKED.
> 
> Is this what we expect?
> 
This is what code does currently. Should we return EINVAL in this case?

--
			Gleb.
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