radix-tree: improve multiorder iterators
This fixes several interlinked problems with the iterators in the
presence of multiorder entries.
1. radix_tree_iter_next() would only advance by one slot, which would
result in the iterators returning the same entry more than once if
there were sibling entries.
2. radix_tree_next_slot() could return an internal pointer instead of
a user pointer if a tagged multiorder entry was immediately followed by
an entry of lower order.
3. radix_tree_next_slot() expanded to a lot more code than it used to
when multiorder support was compiled in. And I wasn't comfortable with
entry_to_node() being in a header file.
Fixing radix_tree_iter_next() for the presence of sibling entries
necessarily involves examining the contents of the radix tree, so we now
need to pass 'slot' to radix_tree_iter_next(), and we need to change the
calling convention so it is called *before* dropping the lock which
protects the tree. Also rename it to radix_tree_iter_resume(), as some
people thought it was necessary to call radix_tree_iter_next() each time
around the loop.
radix_tree_next_slot() becomes closer to how it looked before multiorder
support was introduced. It only checks to see if the next entry in the
chunk is a sibling entry or a pointer to a node; this should be rare
enough that handling this case out of line is not a performance impact
(and such impact is amortised by the fact that the entry we just
processed was a multiorder entry). Also, radix_tree_next_slot() used to
force a new chunk lookup for untagged entries, which is more expensive
than the out of line sibling entry skipping.
Link: http://lkml.kernel.org/r/1480369871-5271-55-git-send-email-mawilcox@linuxonhyperv.com
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/tools/testing/radix-tree/iteration_check.c b/tools/testing/radix-tree/iteration_check.c
index df71cb8..f328a66 100644
--- a/tools/testing/radix-tree/iteration_check.c
+++ b/tools/testing/radix-tree/iteration_check.c
@@ -48,8 +48,8 @@ static void *add_entries_fn(void *arg)
/*
* Iterate over the tagged entries, doing a radix_tree_iter_retry() as we find
* things that have been removed and randomly resetting our iteration to the
- * next chunk with radix_tree_iter_next(). Both radix_tree_iter_retry() and
- * radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
+ * next chunk with radix_tree_iter_resume(). Both radix_tree_iter_retry() and
+ * radix_tree_iter_resume() cause radix_tree_next_slot() to be called with a
* NULL 'slot' variable.
*/
static void *tagged_iteration_fn(void *arg)
@@ -79,7 +79,7 @@ static void *tagged_iteration_fn(void *arg)
}
if (rand_r(&seeds[0]) % 50 == 0) {
- slot = radix_tree_iter_next(&iter);
+ slot = radix_tree_iter_resume(slot, &iter);
rcu_read_unlock();
rcu_barrier();
rcu_read_lock();
@@ -96,8 +96,8 @@ static void *tagged_iteration_fn(void *arg)
/*
* Iterate over the entries, doing a radix_tree_iter_retry() as we find things
* that have been removed and randomly resetting our iteration to the next
- * chunk with radix_tree_iter_next(). Both radix_tree_iter_retry() and
- * radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
+ * chunk with radix_tree_iter_resume(). Both radix_tree_iter_retry() and
+ * radix_tree_iter_resume() cause radix_tree_next_slot() to be called with a
* NULL 'slot' variable.
*/
static void *untagged_iteration_fn(void *arg)
@@ -127,7 +127,7 @@ static void *untagged_iteration_fn(void *arg)
}
if (rand_r(&seeds[1]) % 50 == 0) {
- slot = radix_tree_iter_next(&iter);
+ slot = radix_tree_iter_resume(slot, &iter);
rcu_read_unlock();
rcu_barrier();
rcu_read_lock();