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Date: Wed, 22 Oct 2014 12:49:30 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/4] mm: introduce mm_forbids_zeropage function
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To: Dominik Dingel <dingel@linux.vnet.ibm.com>
Cc: linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.cz>, Paolo Bonzini <pbonzini@redhat.com>, Dave Hansen <dave.hansen@intel.com>, Rik van Riel <riel@redhat.com>, Andrea Arcangeli <aarcange@redhat.com>, Andy Lutomirski <luto@amacapital.net>, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>, Bob Liu <lliubbo@gmail.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Cornelia Huck <cornelia.huck@de.ibm.com>, Gleb Natapov <gleb@kernel.org>, Heiko Carstens <heiko.carstens@de.ibm.com>, "H. Peter Anvin" <hpa@linux.intel.com>, Hugh Dickins <hughd@google.com>, Ingo Molnar <mingo@kernel.org>, Jianyu Zhan <nasa4836@gmail.com>, Johannes Weiner <hannes@cmpxchg.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, kvm@vger.kernel.org, linux390@de.ibm.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Martin Schwidefsky <schwidefsky@de.ibm.com>, Peter Zijlstra <peterz@infradead.org>, Sasha Levin <sasha.levin@oracle.com>

On Wed, 22 Oct 2014 21:45:52 +0200 Dominik Dingel <dingel@linux.vnet.ibm.com> wrote:

> > > +#ifndef mm_forbids_zeropage
> > > +#define mm_forbids_zeropage(X)  (0)
> > > +#endif
> > 
> > Can we document this please?  What it does, why it does it.  We should
> > also specify precisely which arch header file is responsible for
> > defining mm_forbids_zeropage.
> > 
> 
> I will add a comment like:
> 
> /*
>  * To prevent common memory management code establishing
>  * a zero page mapping on a read fault.
>  * This function should be implemented within <asm/pgtable.h>.

s/function should be implemented/macro should be defined/

>  * s390 does this to prevent multiplexing of hardware bits
>  * related to the physical page in case of virtualization.
>  */
> 
> Okay?

Looks great, thanks.

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