radix-tree: add radix_tree_prev_hole()
The counterpart of radix_tree_next_hole(). To be used by context readahead.
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Vladislav Bolkhovitin <vst@vlnb.net>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Ying Han <yinghan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 4bb42a0..5301a52 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -666,6 +666,43 @@
}
EXPORT_SYMBOL(radix_tree_next_hole);
+/**
+ * radix_tree_prev_hole - find the prev hole (not-present entry)
+ * @root: tree root
+ * @index: index key
+ * @max_scan: maximum range to search
+ *
+ * Search backwards in the range [max(index-max_scan+1, 0), index]
+ * for the first hole.
+ *
+ * Returns: the index of the hole if found, otherwise returns an index
+ * outside of the set specified (in which case 'index - return >= max_scan'
+ * will be true). In rare cases of wrap-around, LONG_MAX will be returned.
+ *
+ * radix_tree_next_hole may be called under rcu_read_lock. However, like
+ * radix_tree_gang_lookup, this will not atomically search a snapshot of
+ * the tree at a single point in time. For example, if a hole is created
+ * at index 10, then subsequently a hole is created at index 5,
+ * radix_tree_prev_hole covering both indexes may return 5 if called under
+ * rcu_read_lock.
+ */
+unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan)
+{
+ unsigned long i;
+
+ for (i = 0; i < max_scan; i++) {
+ if (!radix_tree_lookup(root, index))
+ break;
+ index--;
+ if (index == LONG_MAX)
+ break;
+ }
+
+ return index;
+}
+EXPORT_SYMBOL(radix_tree_prev_hole);
+
static unsigned int
__lookup(struct radix_tree_node *slot, void ***results, unsigned long index,
unsigned int max_items, unsigned long *next_index)