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

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Message-ID: <CAMuHMdXnQwKwxKJy+bpPDSw12+jteHmHD6gnMfPgynmbBK70ug@mail.gmail.com>
Date:	Mon, 18 Jan 2016 15:56:53 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	"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)

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>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds