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/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 355f6e80db0d3e8afd4de9d4bcf447ec4e637ea3..c5da7491809655fde7650c0ba65753988b41c4ab 100644 (file)
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -167,6 +167,8 @@ radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
                        unsigned long first_index, unsigned int max_items);
 unsigned long radix_tree_next_hole(struct radix_tree_root *root,
                                unsigned long index, unsigned long max_scan);
+unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
+                               unsigned long index, unsigned long max_scan);
 int radix_tree_preload(gfp_t gfp_mask);
 void radix_tree_init(void);
 void *radix_tree_tag_set(struct radix_tree_root *root,

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 4bb42a0344ec49f5224d74c932786f0842446bef..5301a52cdb4dbafa85d2119d93516e2d8b6508d9 100644 (file)
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -666,6 +666,43 @@ unsigned long radix_tree_next_hole(struct radix_tree_root *root,
 }
 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)