[PATCH] mm: page_state opt docs
Comment the new locking rules for page_state statistics.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index dede8d4..d52999c 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -79,13 +79,23 @@
/*
* Global page accounting. One instance per CPU. Only unsigned longs are
* allowed.
+ *
+ * - Fields can be modified with xxx_page_state and xxx_page_state_zone at
+ * any time safely (which protects the instance from modification by
+ * interrupt.
+ * - The __xxx_page_state variants can be used safely when interrupts are
+ * disabled.
+ * - The __xxx_page_state variants can be used if the field is only
+ * modified from process context, or only modified from interrupt context.
+ * In this case, the field should be commented here.
*/
struct page_state {
unsigned long nr_dirty; /* Dirty writeable pages */
unsigned long nr_writeback; /* Pages under writeback */
unsigned long nr_unstable; /* NFS unstable pages */
unsigned long nr_page_table_pages;/* Pages used for pagetables */
- unsigned long nr_mapped; /* mapped into pagetables */
+ unsigned long nr_mapped; /* mapped into pagetables.
+ * only modified from process context */
unsigned long nr_slab; /* In slab */
#define GET_PAGE_STATE_LAST nr_slab