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Date: Wed, 22 Oct 2014 12:22:23 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/4] mm: introduce mm_forbids_zeropage function
Message-Id: <20141022122223.f3bef0f497941fa8e0805dbf@linux-foundation.org>
In-Reply-To: <1413976170-42501-3-git-send-email-dingel@linux.vnet.ibm.com>
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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 13:09:28 +0200 Dominik Dingel <dingel@linux.vnet.ibm.com> wrote:

> Add a new function stub to allow architectures to disable for
> an mm_structthe backing of non-present, anonymous pages with
> read-only empty zero pages.
> 
> ...
>
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -56,6 +56,10 @@ extern int sysctl_legacy_va_layout;
>  #define __pa_symbol(x)  __pa(RELOC_HIDE((unsigned long)(x), 0))
>  #endif
>  
> +#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.


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