radix-tree,shmem: introduce radix_tree_iter_next()

shmem likes to occasionally drop the lock, schedule, then reacqire the
lock and continue with the iteration from the last place it left off.
This is currently done with a pretty ugly goto.  Introduce
radix_tree_iter_next() and use it throughout shmem.c.

[koct9i@gmail.com: fix bug in radix_tree_iter_next() for tagged iteration]
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.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 b211f14..51a97ac 100644 (file)
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -402,6 +402,22 @@ void **radix_tree_iter_retry(struct radix_tree_iter *iter)
        return NULL;
 }
 
+/**
+ * radix_tree_iter_next - resume iterating when the chunk may be invalid
+ * @iter:      iterator state
+ *
+ * If the iterator needs to release then reacquire a lock, the chunk may
+ * have been invalidated by an insertion or deletion.  Call this function
+ * to continue the iteration from the next index.
+ */
+static inline __must_check
+void **radix_tree_iter_next(struct radix_tree_iter *iter)
+{
+       iter->next_index = iter->index + 1;
+       iter->tags = 0;
+       return NULL;
+}
+
 /**
  * radix_tree_chunk_size - get current chunk size
  *

diff --git a/mm/shmem.c b/mm/shmem.c
index 91c0dad..9428c51 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -376,7 +376,6 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
 
        rcu_read_lock();
 
-restart:
        radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
                if (iter.index >= end)
                        break;
@@ -393,8 +392,7 @@ restart:
 
                if (need_resched()) {
                        cond_resched_rcu();
-                       start = iter.index + 1;
-                       goto restart;
+                       slot = radix_tree_iter_next(&iter);
                }
        }
 
@@ -1944,7 +1942,6 @@ static void shmem_tag_pins(struct address_space *mapping)
        start = 0;
        rcu_read_lock();
 
-restart:
        radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
                page = radix_tree_deref_slot(slot);
                if (!page || radix_tree_exception(page)) {
@@ -1961,8 +1958,7 @@ restart:
 
                if (need_resched()) {
                        cond_resched_rcu();
-                       start = iter.index + 1;
-                       goto restart;
+                       slot = radix_tree_iter_next(&iter);
                }
        }
        rcu_read_unlock();
@@ -1999,7 +1995,6 @@ static int shmem_wait_for_pins(struct address_space *mapping)
 
                start = 0;
                rcu_read_lock();
-restart:
                radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter,
                                           start, SHMEM_TAG_PINNED) {
 
@@ -2033,8 +2028,7 @@ restart:
 continue_resched:
                        if (need_resched()) {
                                cond_resched_rcu();
-                               start = iter.index + 1;
-                               goto restart;
+                               slot = radix_tree_iter_next(&iter);
                        }
                }
                rcu_read_unlock();