page cache: Convert find_get_pages_contig to XArray

There's no direct replacement for radix_tree_for_each_contig()
in the XArray API as it's an unusual thing to do.  Instead,
open-code a loop using xas_next().  This removes the only user of
radix_tree_for_each_contig() so delete the iterator from the API and
the test suite code for it.

Signed-off-by: Matthew Wilcox <willy@infradead.org>

4 files changed, 22 insertions, 72 deletions

diff --git a/.clang-format b/.clang-format
index 1d5da22e0ba5..e6080f5834a3 100644
--- a/.clang-format
+++ b/.clang-format
@@ -323,7 +323,6 @@ ForEachMacros:
   - 'protocol_for_each_card'
   - 'protocol_for_each_dev'
   - 'queue_for_each_hw_ctx'
-  - 'radix_tree_for_each_contig'
   - 'radix_tree_for_each_slot'
   - 'radix_tree_for_each_tagged'
   - 'rbtree_postorder_for_each_entry_safe'
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index d55de428a589..023e888e1163 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -523,23 +523,6 @@ static __always_inline void __rcu **radix_tree_next_slot(void __rcu **slot,
              slot = radix_tree_next_slot(slot, iter, 0))
 
 /**
- * radix_tree_for_each_contig - iterate over contiguous slots
- *
- * @slot:       the void** variable for pointer to slot
- * @root:       the struct radix_tree_root pointer
- * @iter:       the struct radix_tree_iter pointer
- * @start:      iteration starting index
- *
- * @slot points to radix tree slot, @iter->index contains its index.
- */
-#define radix_tree_for_each_contig(slot, root, iter, start)             \
-        for (slot = radix_tree_iter_init(iter, start) ;                 \
-             slot || (slot = radix_tree_next_chunk(root, iter,          \
-                                RADIX_TREE_ITER_CONTIG)) ;              \
-             slot = radix_tree_next_slot(slot, iter,                    \
-                                RADIX_TREE_ITER_CONTIG))
-
-/**
  * radix_tree_for_each_tagged - iterate over tagged slots
  *
  * @slot:       the void** variable for pointer to slot
diff --git a/mm/filemap.c b/mm/filemap.c
index b72c39fe61c2..089b67598100 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1721,57 +1721,43 @@ out:
 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
                                unsigned int nr_pages, struct page **pages)
 {
-        struct radix_tree_iter iter;
-        void **slot;
+        XA_STATE(xas, &mapping->i_pages, index);
+        struct page *page;
         unsigned int ret = 0;
 
         if (unlikely(!nr_pages))
                 return 0;
 
         rcu_read_lock();
-        radix_tree_for_each_contig(slot, &mapping->i_pages, &iter, index) {
-                struct page *head, *page;
-repeat:
-                page = radix_tree_deref_slot(slot);
-                /* The hole, there no reason to continue */
-                if (unlikely(!page))
-                        break;
-
-                if (radix_tree_exception(page)) {
-                        if (radix_tree_deref_retry(page)) {
-                                slot = radix_tree_iter_retry(&iter);
-                                continue;
-                        }
-                        /*
-                         * A shadow entry of a recently evicted page,
-                         * or a swap entry from shmem/tmpfs.  Stop
-                         * looking for contiguous pages.
-                         */
+        for (page = xas_load(&xas); page; page = xas_next(&xas)) {
+                struct page *head;
+                if (xas_retry(&xas, page))
+                        continue;
+                /*
+                 * If the entry has been swapped out, we can stop looking.
+                 * No current caller is looking for DAX entries.
+                 */
+                if (xa_is_value(page))
                         break;
-                }
 
                 head = compound_head(page);
                 if (!page_cache_get_speculative(head))
-                        goto repeat;
+                        goto retry;
 
                 /* The page was split under us? */
-                if (compound_head(page) != head) {
-                        put_page(head);
-                        goto repeat;
-                }
+                if (compound_head(page) != head)
+                        goto put_page;
 
                 /* Has the page moved? */
-                if (unlikely(page != *slot)) {
-                        put_page(head);
-                        goto repeat;
-                }
+                if (unlikely(page != xas_reload(&xas)))
+                        goto put_page;
 
                 /*
                  * must check mapping and index after taking the ref.
                  * otherwise we can get both false positives and false
                  * negatives, which is just confusing to the caller.
                  */
-                if (page->mapping == NULL || page_to_pgoff(page) != iter.index) {
+                if (!page->mapping || page_to_pgoff(page) != xas.xa_index) {
                         put_page(page);
                         break;
                 }
@@ -1779,6 +1765,11 @@ repeat:
                 pages[ret] = page;
                 if (++ret == nr_pages)
                         break;
+                continue;
+put_page:
+                put_page(head);
+retry:
+                xas_reset(&xas);
         }
         rcu_read_unlock();
         return ret;
diff --git a/tools/testing/radix-tree/regression3.c b/tools/testing/radix-tree/regression3.c
index ace2543c3eda..9f9a3b280f56 100644
--- a/tools/testing/radix-tree/regression3.c
+++ b/tools/testing/radix-tree/regression3.c
@@ -69,21 +69,6 @@ void regression3_test(void)
                         continue;
                 }
         }
-        radix_tree_delete(&root, 1);
-
-        first = true;
-        radix_tree_for_each_contig(slot, &root, &iter, 0) {
-                printv(2, "contig %ld %p\n", iter.index, *slot);
-                if (first) {
-                        radix_tree_insert(&root, 1, ptr);
-                        first = false;
-                }
-                if (radix_tree_deref_retry(*slot)) {
-                        printv(2, "retry at %ld\n", iter.index);
-                        slot = radix_tree_iter_retry(&iter);
-                        continue;
-                }
-        }
 
         radix_tree_for_each_slot(slot, &root, &iter, 0) {
                 printv(2, "slot %ld %p\n", iter.index, *slot);
@@ -93,14 +78,6 @@ void regression3_test(void)
                 }
         }
 
-        radix_tree_for_each_contig(slot, &root, &iter, 0) {
-                printv(2, "contig %ld %p\n", iter.index, *slot);
-                if (!iter.index) {
-                        printv(2, "next at %ld\n", iter.index);
-                        slot = radix_tree_iter_resume(slot, &iter);
-                }
-        }
-
         radix_tree_tag_set(&root, 0, 0);
         radix_tree_tag_set(&root, 1, 0);
         radix_tree_for_each_tagged(slot, &root, &iter, 0, 0) {