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Date: Tue, 22 Mar 2005 10:34:23 -0800
From: "David S. Miller" <davem@davemloft.net>
To: Hugh Dickins <hugh@veritas.com>
Cc: akpm@osdl.org, nickpiggin@yahoo.com.au, tony.luck@intel.com,
       benh@kernel.crashing.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] freepgt: free_pgtables use vma list
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On Tue, 22 Mar 2005 16:37:09 +0000 (GMT)
Hugh Dickins <hugh@veritas.com> wrote:

> If you and David could try the lame patch below,
> it'll at least give us a slight clue of where to be looking -
> every mm exiting with nr_ptes 1 means something different from
> every mm exiting with nr_ptes -1 means something different from
> occasional mms exiting with nr_ptes something positive.

I didn't use your debugging patch, I used something slightly
more sophisticated to simply traces nr_ptes counter bumps
then halt the system when the BUG_ON(mm->nr_ptes) triggered
so I could analyze things.

What happens is (all virtual addresses are PMD_MASK'd):

1) We map 3 PTE tables.
   0x0000000000000000
   0x0000000070000000
   0x00000000ef800000
2) We only unmap one PTE table.
   0x0000000000000000
3) Then we of course BUG() because nr_ptes is 2

I'm now adding more debugging to figure out why only the
first PTE table is being unmapped.