Messages in this thread | | | Date | Fri, 15 May 2015 14:37:15 +0200 | From | Vlastimil Babka <> | Subject | Re: [PATCHv5 01/28] mm, proc: adjust PSS calculation |
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On 05/15/2015 01:43 PM, Kirill A. Shutemov wrote: > On Fri, May 15, 2015 at 01:33:31PM +0200, Vlastimil Babka wrote: >> 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@linux.intel.com> >>>>> Tested-by: Sasha Levin <sasha.levin@oracle.com> >>>> >>>> Acked-by: Vlastimil Babka <vbabka@suse.cz> >>>> >>>> (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? > > Kernel relies on dead-code elimination. You cannot build kernel with -O0.
Ah, OK.
>> 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... > > I think we could try to downgrade it BUG(). Although I found BUILD_BUG() > useful few times.
BUILD_BUG() seems like a better match here. Better than pollute the code for THP=n (in case of Patch 3 where it doesn't eliminate).
> HPAGE_PMD_NR==1 would be just wrong. It would mean you can map order-0 > page with PMD %-|
That's why I suggested a different variant of the "variable".
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