Messages in this thread | | | Date | Thu, 27 Aug 2015 17:19:04 +0200 | From | Michal Hocko <> | Subject | Re: [PATCHv4 7/7] mm: use 'unsigned int' for compound_dtor/compound_order on 64BIT |
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On Thu 27-08-15 16:59:21, Kirill A. Shutemov wrote: > On 64 bit system we have enough space in struct page to encode > compound_dtor and compound_order with unsigned int. > > On x86-64 it leads to slightly smaller code size due usesage of plain > MOV instead of MOVZX (zero-extended move) or similar effect. > > allyesconfig: > > text data bss dec hex filename > 159520446 48146736 72196096 279863278 10ae5fee vmlinux.pre > 159520382 48146736 72196096 279863214 10ae5fae vmlinux.post
64B is not much, really, but if that works as a microptimization then I have no objections.
> On other architectures without native support of 16-bit data types the > difference can be bigger.
Thank you for pulling this out of the original patch.
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
> --- > include/linux/mm_types.h | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index ecaf3b1d0216..39b0db74ba5e 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -150,8 +150,13 @@ struct page { > /* First tail page of compound page */ > struct { > unsigned long compound_head; /* If bit zero is set */ > +#ifdef CONFIG_64BIT > + unsigned int compound_dtor; > + unsigned int compound_order; > +#else > unsigned short int compound_dtor; > unsigned short int compound_order; > +#endif > }; > > #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && USE_SPLIT_PMD_PTLOCKS > -- > 2.5.0
-- Michal Hocko SUSE Labs
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