linux-kernel - Re: BUILD_BUG() in smaps_account() (was: Re: [PATCHv12 01/37] mm, proc: adjust PSS calculation)

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Date:	Thu, 21 Jan 2016 11:31:46 -0800
From:	Tony Luck <tony.luck@...il.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>
Subject: Re: BUILD_BUG() in smaps_account() (was: Re: [PATCHv12 01/37] mm,
 proc: adjust PSS calculation)

On Mon, Jan 18, 2016 at 6:56 AM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> Hi Kirill,
>
> On Mon, Jan 18, 2016 at 12:40 PM, Kirill A. Shutemov
> <kirill@...temov.name> wrote:
>> On Mon, Jan 18, 2016 at 11:09:00AM +0100, Geert Uytterhoeven wrote:
>>>     fs/built-in.o: In function `smaps_account':
>>>     task_mmu.c:(.text+0x4f8fa): undefined reference to
>>> `__compiletime_assert_471'
>>>
>>> Seen with m68k/allmodconfig or allyesconfig and gcc version 4.1.2 20061115
>>> (prerelease) (Ubuntu 4.1.1-21).
>>> Not seen when compiling the affected file with gcc 4.6.3 or 4.9.0, or with the
>>> m68k defconfigs.
>>
>> Ughh.
>>
>> Please, test this:
>>
>> From 5ac27019f886eef033e84c9579e09099469ccbf9 Mon Sep 17 00:00:00 2001
>> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>> Date: Mon, 18 Jan 2016 14:32:49 +0300
>> Subject: [PATCH] mm, proc: add workaround for old compilers
>>
>> For THP=n, HPAGE_PMD_NR in smaps_account() expands to BUILD_BUG().
>> That's fine since this codepath is eliminated by modern compilers.
>>
>> But older compilers have not that efficient dead code elimination.
>> It causes problem at least with gcc 4.1.2 on m68k.
>>
>> Let's replace HPAGE_PMD_NR with 1 << compound_order(page).
>>
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>
> Thanks, that fixes it!
>
> Tested-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Same breakage on ia64 (with gcc 4.3.4).  Same fix works for me.

Tested-by: Tony Luck <tony.luck@...el.com>