Re: [PATCH 6/7] radixtree: introduce radix_tree_scan_hole()

Fengguang Wu
2007-07-23T08:16:14Z

On Mon, Jul 23, 2007 at 05:58:02PM +1000, Nick Piggin wrote:
> Fengguang Wu wrote:
> >Introduce radix_tree_scan_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.
>
> Reasonable function to want. Is radix_tree_scan_hole the best name?
> What about radix_tree_next_hole or _find_next_hole? (Andrew, any
> suggestions?)

Thank you!

All comments seems reasonable, so I simply attach the updated patch.

Fengguang
---
Subject: radixtree: introduce radix_tree_next_hole()
Cc: Nick Piggin <nickpiggin@yahoo.com.au>

Introduce radix_tree_next_hole(root, index, max_scan) to scan radix tree
for the first hole. It will be used in interleaved readahead.

Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---

include/linux/radix-tree.h | 2 +
lib/radix-tree.c | 36 +++++++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+)

--- linux-2.6.22-rc6-mm1.orig/include/linux/radix-tree.h
+++ linux-2.6.22-rc6-mm1/include/linux/radix-tree.h
@@ -155,6 +155,8 @@ void *radix_tree_delete(struct radix_tre
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,
--- linux-2.6.22-rc6-mm1.orig/lib/radix-tree.c
+++ linux-2.6.22-rc6-mm1/lib/radix-tree.c
@@ -601,6 +601,42 @@ int radix_tree_tag_get(struct radix_tree
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)