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Date: Wed, 23 Mar 2005 10:32:10 +1100
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Hugh Dickins <hugh@veritas.com>
CC: "David S. Miller" <davem@davemloft.net>, akpm@osdl.org,
       tony.luck@intel.com, benh@kernel.crashing.org,
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Subject: Re: [PATCH 1/5] freepgt: free_pgtables use vma list
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Hugh Dickins wrote:
> On Tue, 22 Mar 2005, David S. Miller wrote:
> 
>>On Tue, 22 Mar 2005 19:36:46 +0000 (GMT)
>>Hugh Dickins <hugh@veritas.com> wrote:
>>
>>
>>>I notice that although both i386 and sparc64 use pgtable-nopud.h, the
>>>i386 pud_clear does nothing at all and the sparc64 pud_clear resets to 0.
>>
>>This was a dead end.  I386 doesn't do anything with pud_clear() in
>>order to work around a chip erratum.
>>
>>IA64 does clear in pud_clear() just like sparc64.
> 
> 
> My mind kept flipping back and forth on whether it was pud_clear().
> I agree, I can't see that it's the issue now.
> 

It shouldn't be.

In the case that pud is folded, free_pud_range will only call into
free_pmd_range once, and that function will loop over the required
range of the pud (ie. the pmd). If it then also falls through to
pud_clear in that function, it will also fall through to pgd_clear
in free_pud_range. So it doesn't _really_ matter which one does the
actual clearing in that case.

I think David's on the right track - I think there's something a
bit wrong at the top. In my reply to Andrew in this thread I
posted a patch which may at least get things working...