**diff options**

-rw-r--r-- | include/linux/radix-tree.h | 38 |

1 files changed, 23 insertions, 15 deletions

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h index c2f69e25ba86..cb4b7e8cee81 100644 --- a/include/linux/radix-tree.h +++ b/include/linux/radix-tree.h @@ -29,28 +29,37 @@ #include <linux/rcupdate.h> /* - * Entries in the radix tree have the low bit set if they refer to a - * radix_tree_node. If the low bit is clear then the entry is user data. - * - * We also use the low bit to indicate that the slot will be freed in the - * next RCU idle period, and users need to re-walk the tree to find the - * new slot for the index that they were looking for. See the comment in - * radix_tree_shrink() for details. + * The bottom two bits of the slot determine how the remaining bits in the + * slot are interpreted: + * + * 00 - data pointer + * 01 - internal entry + * 10 - exceptional entry + * 11 - locked exceptional entry + * + * The internal entry may be a pointer to the next level in the tree, a + * sibling entry, or an indicator that the entry in this slot has been moved + * to another location in the tree and the lookup should be restarted. While + * NULL fits the 'data pointer' pattern, it means that there is no entry in + * the tree for this index (no matter what level of the tree it is found at). + * This means that you cannot store NULL in the tree as a value for the index. */ -#define RADIX_TREE_INTERNAL_NODE 1 +#define RADIX_TREE_ENTRY_MASK 3UL +#define RADIX_TREE_INTERNAL_NODE 1UL /* - * A common use of the radix tree is to store pointers to struct pages; - * but shmem/tmpfs needs also to store swap entries in the same tree: - * those are marked as exceptional entries to distinguish them. + * Most users of the radix tree store pointers but shmem/tmpfs stores swap + * entries in the same tree. They are marked as exceptional entries to + * distinguish them from pointers to struct page. * EXCEPTIONAL_ENTRY tests the bit, EXCEPTIONAL_SHIFT shifts content past it. */ #define RADIX_TREE_EXCEPTIONAL_ENTRY 2 #define RADIX_TREE_EXCEPTIONAL_SHIFT 2 -static inline int radix_tree_is_internal_node(void *ptr) +static inline bool radix_tree_is_internal_node(void *ptr) { - return (int)((unsigned long)ptr & RADIX_TREE_INTERNAL_NODE); + return ((unsigned long)ptr & RADIX_TREE_ENTRY_MASK) == + RADIX_TREE_INTERNAL_NODE; } /*** radix-tree API starts here ***/ @@ -236,8 +245,7 @@ static inline int radix_tree_exceptional_entry(void *arg) */ static inline int radix_tree_exception(void *arg) { - return unlikely((unsigned long)arg & - (RADIX_TREE_INTERNAL_NODE | RADIX_TREE_EXCEPTIONAL_ENTRY)); + return unlikely((unsigned long)arg & RADIX_TREE_ENTRY_MASK); } /** |