Messages in this thread Patch in this message | | | From | "Kirill A. Shutemov" <> | Subject | [PATCHv6 7/7] mm: use 'unsigned int' for compound_dtor/compound_order on 64BIT | Date | Tue, 15 Sep 2015 13:28:15 +0300 |
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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
On other architectures without native support of 16-bit data types the difference can be bigger.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> --- include/linux/mm_types.h | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 385604afbafa..82d7f6a72626 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -143,8 +143,19 @@ struct page { unsigned long compound_head; /* If bit zero is set */ /* First tail page only */ +#ifdef CONFIG_64BIT + /* + * On 64 bit system we have enough space in struct page + * to encode compound_dtor and compound_order with + * unsigned int. It can help compiler generate better or + * smaller code on some archtectures. + */ + 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 -- 2.5.1
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