- * locked- and dirty-page accounting.
- *
- * The page flags field is split into two parts, the main flags area
- * which extends from the low bits upwards, and the fields area which
- * extends from the high bits downwards.
- *
- * | FIELD | ... | FLAGS |
- * N-1 ^ 0
- * (N-FLAGS_RESERVED)
- *
- * The fields area is reserved for fields mapping zone, node and SPARSEMEM
- * section. The boundry between these two areas is defined by
- * FLAGS_RESERVED which defines the width of the fields section
- * (see linux/mmzone.h). New flags must _not_ overlap with this area.
+ * locked- and dirty-page accounting. The top eight bits of page->flags are
+ * used for page->zone, so putting flag bits there doesn't work.