[PATCH] mm: page_state opt docs
Nick Piggin [Fri, 6 Jan 2006 08:11:21 +0000 (00:11 -0800)]
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>

include/linux/page-flags.h

index dede8d4..d52999c 100644 (file)
 /*
  * 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