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Subject: Re: [PATCH 12/13] maps#2: Add /proc/pid/pagemap interface
From: Dave Hansen <hansendc@us.ibm.com>
To: Matt Mackall <mpm@selenic.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
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Date: Thu, 19 Apr 2007 12:12:29 -0700
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On Fri, 2007-04-06 at 17:03 -0500, Matt Mackall wrote:
> 
> +static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned
> long end,
> +                            void *private)
> +{
> +       struct pagemapread *pm = private;
> +       pte_t *pte;
> +       int err;
> +
> +       pte = pte_offset_map(pmd, addr);
> +       for (; addr != end; pte++, addr += PAGE_SIZE) {
> +               if (addr < pm->next)
> +                       continue;
> +               if (!pte_present(*pte))
> +                       err = add_to_pagemap(addr, -1, pm);
> +               else
> +                       err = add_to_pagemap(addr, pte_pfn(*pte), pm);
> +               if (err)
> +                       return err;
> +       }
> +       pte_unmap(pte - 1);
> +       return 0;
> +} 

Sorry for the horribly late reply. ;)

Would you have any problems with this being extended for the !
pte_present() case to show pages that happen to be in swap?

I'm playing with some process checkpoint/restart code, and using the
existing swap mechanisms to get the current memory contents out of the
process.  I've also created a hackish syscall to make a pretty raw dump
of pte contents.

Perhaps we could steal the high bits of the pfn and have its presence in
swap, plus some handle to which swapfile it is in.  Or, would you rather
I just create a new /proc file that utilizes most of the code you
already put in place, and _just_ deals with swap?

-- Dave