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Date: Thu, 23 Apr 2015 15:11:18 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Zhang Zhen <zhenzhang.zhang@huawei.com>
Cc: Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        <cmetcalf@ezchip.com>, David Rientjes <rientjes@google.com>,
        <James.Yang@freescale.com>, <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: [PATCH] mm/hugetlb: reduce arch dependent code about
 huge_pmd_unshare
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On Tue, 14 Apr 2015 15:35:04 +0800 Zhang Zhen <zhenzhang.zhang@huawei.com> wrote:

> Currently we have many duplicates in definitions of huge_pmd_unshare.
> In all architectures this function just returns 0 when
> CONFIG_ARCH_WANT_HUGE_PMD_SHARE is N.
> 
> This patch put the default implementation in mm/hugetlb.c and lets
> these architecture use the common code.

Memory fails me.  Why do some architectures (arm, arm64, x86_64) want
huge_pmd_[un]share() while other architectures (ia64, tile, mips,
powerpc, metag, sh, s390) do not?