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@xxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
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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