Date: Wed, 6 Apr 2016 13:56:59 +0200
From: Gerald Schaefer <gerald.schaefer@de.ibm.com>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andres Lagar-Cavilla <andreslc@google.com>,
        Yang Shi <yang.shi@linaro.org>, Ning Qu <quning@gmail.com>,
        Arnd Bergman <arnd@arndb.de>, Ralf Baechle <ralf@linux-mips.org>,
        Vineet Gupta <vgupta@synopsys.com>,
        Russell King <linux@arm.linux.org.uk>,
        Will Deacon <will.deacon@arm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        David Miller <davem@davemloft.net>,
        Chris Metcalf <cmetcalf@tilera.com>, Ingo Molnar <mingo@kernel.org>,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 10/10] arch: fix has_transparent_hugepage()
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On Tue, 5 Apr 2016 14:02:49 -0700 (PDT)
Hugh Dickins <hughd@google.com> wrote:

> I've just discovered that the useful-sounding has_transparent_hugepage()
> is actually an architecture-dependent minefield: on some arches it only
> builds if CONFIG_TRANSPARENT_HUGEPAGE=y, on others it's also there when
> not, but on some of those (arm and arm64) it then gives the wrong answer;
> and on mips alone it's marked __init, which would crash if called later
> (but so far it has not been called later).
> 
> Straighten this out: make it available to all configs, with a sensible
> default in asm-generic/pgtable.h, removing its definitions from those
> arches (arc, arm, arm64, sparc, tile) which are served by the default,
> adding #define has_transparent_hugepage has_transparent_hugepage to those
> (mips, powerpc, s390, x86) which need to override the default at runtime,
> and removing the __init from mips (but maybe that kind of code should be
> avoided after init: set a static variable the first time it's called).
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>
> ---

Acked-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> # for arch/s390 bits