Re: [PATCHv5 01/28] mm, proc: adjust PSS calculation

[Vlastimil Babka]

On 05/15/2015 12:56 PM, Kirill A. Shutemov wrote:
> On Thu, May 14, 2015 at 04:12:29PM +0200, Vlastimil Babka wrote:
> > On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> > > With new refcounting all subpages of the compound page are not nessessary
> > > 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>
> >
> > Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> >
> > (some nitpicks below)
> >
> > > ---
> > >   fs/proc/task_mmu.c | 43 ++++++++++++++++++++++---------------------
> > >   1 file changed, 22 insertions(+), 21 deletions(-)
> > >
> > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > > index 956b75d61809..95bc384ee3f7 100644
> > > --- a/fs/proc/task_mmu.c
> > > +++ b/fs/proc/task_mmu.c
> > > @@ -449,9 +449,10 @@ 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_nr_pages(page) : 1;
> >
> > Why not just HPAGE_PMD_NR instead of hpage_nr_pages(page)?
>
> Okay, makes sense. Compiler is smart enough to optimize away HPAGE_PMD_NR
> for THP=n. (HPAGE_PMD_NR is BUILD_BUG() for THP=n)

Ah, BUILD_BUG()... I'm not sure we can rely on optimization to avoid 
BUILD_BUG(), what if somebody compiles with all optimizations off?
So why not replace BUILD_BUG() with "1", or create a variant of 
HPAGE_PMD_NR that does that, for this case and patch 3. Seems better 
than testing PageTransHuge everywhere...
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