linux-kernel - Re: [PATCH] mm/pagewalk.c: walk_page_range should avoid VM

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Date:	Wed, 1 May 2013 11:44:56 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Cliff Wickman <cpw@....com>
cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mgorman@...e.de, aarcange@...hat.com, dave.hansen@...el.com,
	dsterba@...e.cz, hannes@...xchg.org, kosaki.motohiro@...il.com,
	kirill.shutemov@...ux.intel.com, mpm@...enic.com,
	n-horiguchi@...jp.nec.com, rdunlap@...radead.org
Subject: Re: [PATCH] mm/pagewalk.c: walk_page_range should avoid VM_PFNMAP
 areas

On Wed, 1 May 2013, Cliff Wickman wrote:

> > > @@ -200,28 +184,46 @@ int walk_page_range(unsigned long addr,
> > >  
> > >  	pgd = pgd_offset(walk->mm, addr);
> > >  	do {
> > > -		struct vm_area_struct *vma;
> > > +		struct vm_area_struct *vma = NULL;
> > >  
> > >  		next = pgd_addr_end(addr, end);
> > >  
> > >  		/*
> > > -		 * handle hugetlb vma individually because pagetable walk for
> > > -		 * the hugetlb page is dependent on the architecture and
> > > -		 * we can't handled it in the same manner as non-huge pages.
> > > +		 * Check any special vma's within this range.
> > >  		 */
> > > -		vma = hugetlb_vma(addr, walk);
> > > +		VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
> > 
> > I think this should be moved out of the iteration.  It's currently inside 
> > it even before your patch, but I think it's pointless.
> 
> I don't follow.  We are iterating through a range of addresses.  When
> we come to a range that is VM_PFNMAP we skip it.  How can we take that
> out of the iteration?
>  

I'm referring only to the VM_BUG_ON().
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