linux-kernel - Re: [PATCH 13/13] maps#2: Add /proc/kpagemap interface

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Message-ID: <20070419200226.GG11115@waste.org>
Date:	Thu, 19 Apr 2007 15:02:26 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Dave Hansen <hansendc@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/13] maps#2: Add /proc/kpagemap interface

On Thu, Apr 19, 2007 at 12:06:38PM -0700, Dave Hansen wrote:
> On Fri, 2007-04-06 at 17:03 -0500, Matt Mackall wrote:
> > 
> > +static ssize_t kpagemap_read(struct file *file, char __user *buf,
> > +                            size_t count, loff_t *ppos)
> > +{
> ...
> > +               for (; i < 2 * chunk / KPMSIZE; i += 2, pfn++) {
> > +                       ppage = pfn_to_page(pfn);
> > +                       if (!ppage) {
> > +                               page[i] = 0;
> > +                               page[i + 1] = 0;
> > +                       } else {
> > +                               page[i] = ppage->flags;
> > +                               page[i + 1] = atomic_read(&ppage->_count);
> > +                       }
> > +               } 
> 
> I think this needs a pfn_valid() check for sparse/discontig systems.  I
> think we'll oops if we have holes because we don't check pfn_valid()
> inside of pfn_to_page().

Are there cases where pfn_valid is true but pfn_to_page doesn't work?
In other words, do I still only need two cases?

-- 
Mathematics is the supreme nostalgia of our time.
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