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authorFengguang Wu <wfg@mail.ustc.edu.cn>2007-10-16 01:24:33 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-16 09:42:52 -0700
commit6df8ba4f8a4c4abca9ccad10441d0dddbdff301c (patch)
tree6ac5cd48d3400a9d32f8affd31106f7942df9547
parentf4e6b498d6e06742d72706ef50593a9c4dd72214 (diff)
radixtree: introduce radix_tree_next_hole()
Introduce radix_tree_next_hole(root, index, max_scan) to scan radix tree for the first hole. It will be used in interleaved readahead. The implementation is dumb and obviously correct. It can help debug(and document) the possible smart one in future. Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/radix-tree.h2
-rw-r--r--lib/radix-tree.c36
2 files changed, 38 insertions, 0 deletions
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index f9e77d2ee320..430e4a8c1382 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -155,6 +155,8 @@ void *radix_tree_delete(struct radix_tree_root *, unsigned long);
unsigned int
radix_tree_gang_lookup(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);
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 514efb200be6..7af368a4401b 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -599,6 +599,42 @@ int radix_tree_tag_get(struct radix_tree_root *root,
EXPORT_SYMBOL(radix_tree_tag_get);
#endif
+/**
+ * radix_tree_next_hole - find the next hole (not-present entry)
+ * @root: tree root
+ * @index: index key
+ * @max_scan: maximum range to search
+ *
+ * Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the lowest
+ * indexed hole.
+ *
+ * Returns: the index of the hole if found, otherwise returns an index
+ * outside of the set specified (in which case 'return - index >= max_scan'
+ * will be true).
+ *
+ * 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
+ * 5, then subsequently a hole is created at index 10, radix_tree_next_hole
+ * covering both indexes may return 10 if called under rcu_read_lock.
+ */
+unsigned long radix_tree_next_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 == 0)
+ break;
+ }
+
+ return index;
+}
+EXPORT_SYMBOL(radix_tree_next_hole);
+
static unsigned int
__lookup(struct radix_tree_node *slot, void **results, unsigned long index,
unsigned int max_items, unsigned long *next_index)