[PATCHv4 7/7] mm: use 'unsigned int' for compound_dtor/compound_order on 64BIT

From: Kirill A. Shutemov
Date: Thu Aug 27 2015 - 10:00:42 EST

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.


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>
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;
unsigned short int compound_dtor;
unsigned short int compound_order;


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/