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

[Kirill A. Shutemov]

On Mon, Jan 18, 2016 at 11:09:00AM +0100, Geert Uytterhoeven wrote:
> Hi Kirill,
> 
> On Tue, Oct 6, 2015 at 5:23 PM, Kirill A. Shutemov
> <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> > With new refcounting all subpages of the compound page are not necessary
> > have the same mapcount. We need to take into account mapcount of every
> > sub-page.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
> > Tested-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> > Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
> > Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> > ---
> >  fs/proc/task_mmu.c | 47 +++++++++++++++++++++++++++++++----------------
> >  1 file changed, 31 insertions(+), 16 deletions(-)
> >
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index bd167675a06f..ace02a4a07db 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -454,9 +454,10 @@ struct mem_size_stats {
> >  };
> >
> >  static void smaps_account(struct mem_size_stats *mss, struct page *page,
> > -               unsigned long size, bool young, bool dirty)
> > +               bool compound, bool young, bool dirty)
> >  {
> > -       int mapcount;
> > +       int i, nr = compound ? HPAGE_PMD_NR : 1;
> 
> If CONFIG_TRANSPARENT_HUGEPAGE is not set, we have:
> 
>     #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
>     #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
>     #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
> 
> Depending on compiler version and optimization level, the BUILD_BUG() may be
> optimized away (smaps_account() is always called with compound = false if
> CONFIG_TRANSPARENT_HUGEPAGE=n), or lead to a build failure:
> 
>     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: