Messages in this thread | | | Date | Fri, 15 May 2015 14:43:14 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCHv5 01/28] mm, proc: adjust PSS calculation |
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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.
> 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.
HPAGE_PMD_NR==1 would be just wrong. It would mean you can map order-0 page with PMD %-|
-- Kirill A. Shutemov
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