diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/highmem.h | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/include/linux/highmem.h b/include/linux/highmem.h index 216a647ed7db..d2209ae8be99 100644 --- a/include/linux/highmem.h +++ b/include/linux/highmem.h @@ -32,6 +32,7 @@ static inline void invalidate_kernel_vmap_range(void *vaddr, int size) #include <asm/kmap_types.h> #ifdef CONFIG_HIGHMEM +extern void *kmap_atomic_high(struct page *page); #include <asm/highmem.h> #ifndef ARCH_HAS_KMAP_FLUSH_TLB @@ -62,6 +63,28 @@ static inline void kunmap(struct page *page) kunmap_high(page); } +/* + * kmap_atomic/kunmap_atomic is significantly faster than kmap/kunmap because + * no global lock is needed and because the kmap code must perform a global TLB + * invalidation when the kmap pool wraps. + * + * However when holding an atomic kmap is is not legal to sleep, so atomic + * kmaps are appropriate for short, tight code paths only. + * + * The use of kmap_atomic/kunmap_atomic is discouraged - kmap/kunmap + * gives a more generic (and caching) interface. But kmap_atomic can + * be used in IRQ contexts, so in some (very limited) cases we need + * it. + */ +static inline void *kmap_atomic(struct page *page) +{ + preempt_disable(); + pagefault_disable(); + if (!PageHighMem(page)) + return page_address(page); + return kmap_atomic_high(page); +} + /* declarations for linux/mm/highmem.c */ unsigned int nr_free_highpages(void); extern atomic_long_t _totalhigh_pages; |