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-rw-r--r--include/linux/highmem.h23
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;