diff options
| -rw-r--r-- | include/linux/page-flags.h | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 547aac7696cd..d276a4e2f825 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -48,8 +48,20 @@ /* * Don't use the *_dontuse flags. Use the macros. Otherwise you'll break - * 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. + * 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. */ #define PG_locked 0 /* Page is locked. Don't touch. */ #define PG_error 1 |