diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/mm.h | 41 |
1 files changed, 38 insertions, 3 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index e6b6be15609e..abb7eb7ef0f2 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -124,10 +124,45 @@ extern int mmap_rnd_compat_bits __read_mostly; /* * On some architectures it is expensive to call memset() for small sizes. - * Those architectures should provide their own implementation of "struct page" - * zeroing by defining this macro in <asm/pgtable.h>. + * If an architecture decides to implement their own version of + * mm_zero_struct_page they should wrap the defines below in a #ifndef and + * define their own version of this macro in <asm/pgtable.h> */ -#ifndef mm_zero_struct_page +#if BITS_PER_LONG == 64 +/* This function must be updated when the size of struct page grows above 80 + * or reduces below 56. The idea that compiler optimizes out switch() + * statement, and only leaves move/store instructions. Also the compiler can + * combine write statments if they are both assignments and can be reordered, + * this can result in several of the writes here being dropped. + */ +#define mm_zero_struct_page(pp) __mm_zero_struct_page(pp) +static inline void __mm_zero_struct_page(struct page *page) +{ + unsigned long *_pp = (void *)page; + + /* Check that struct page is either 56, 64, 72, or 80 bytes */ + BUILD_BUG_ON(sizeof(struct page) & 7); + BUILD_BUG_ON(sizeof(struct page) < 56); + BUILD_BUG_ON(sizeof(struct page) > 80); + + switch (sizeof(struct page)) { + case 80: + _pp[9] = 0; /* fallthrough */ + case 72: + _pp[8] = 0; /* fallthrough */ + case 64: + _pp[7] = 0; /* fallthrough */ + case 56: + _pp[6] = 0; + _pp[5] = 0; + _pp[4] = 0; + _pp[3] = 0; + _pp[2] = 0; + _pp[1] = 0; + _pp[0] = 0; + } +} +#else #define mm_zero_struct_page(pp) ((void)memset((pp), 0, sizeof(struct page))) #endif |