XArray: Add private interface for workingset node deletion

Move the tricky bits of dealing with the XArray from the workingset
code to the XArray.  Make it clear in the documentation that this is a
private interface, and only export it for the benefit of the test suite.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

include/linux/xarray.h

@@ -1286,6 +1286,8 @@ static inline bool xa_is_advanced(const void *entry)
  */
 typedef void (*xa_update_node_t)(struct xa_node *node);
 
+void xa_delete_node(struct xa_node *, xa_update_node_t);
+
 /*
  * The xa_state is opaque to its users.  It contains various different pieces
  * of state involved in the current operation on the XArray.  It should be

lib/test_xarray.c

@@ -1600,14 +1600,9 @@ static noinline void shadow_remove(struct xarray *xa)
 	xa_lock(xa);
 	while ((node = list_first_entry_or_null(&shadow_nodes,
 					struct xa_node, private_list))) {
-		XA_STATE(xas, node->array, 0);
 		XA_BUG_ON(xa, node->array != xa);
 		list_del_init(&node->private_list);
-		xas.xa_node = xa_parent_locked(node->array, node);
-		xas.xa_offset = node->offset;
-		xas.xa_shift = node->shift + XA_CHUNK_SHIFT;
-		xas_set_update(&xas, test_update_node);
-		xas_store(&xas, NULL);
+		xa_delete_node(node, test_update_node);
 	}
 	xa_unlock(xa);
 }

lib/xarray.c

@@ -1973,6 +1973,29 @@ unsigned int xa_extract(struct xarray *xa, void **dst, unsigned long start,
 }
 EXPORT_SYMBOL(xa_extract);
 
+/**
+ * xa_delete_node() - Private interface for workingset code.
+ * @node: Node to be removed from the tree.
+ * @update: Function to call to update ancestor nodes.
+ *
+ * Context: xa_lock must be held on entry and will not be released.
+ */
+void xa_delete_node(struct xa_node *node, xa_update_node_t update)
+{
+	struct xa_state xas = {
+		.xa = node->array,
+		.xa_index = (unsigned long)node->offset <<
+				(node->shift + XA_CHUNK_SHIFT),
+		.xa_shift = node->shift + XA_CHUNK_SHIFT,
+		.xa_offset = node->offset,
+		.xa_node = xa_parent_locked(node->array, node),
+		.xa_update = update,
+	};
+
+	xas_store(&xas, NULL);
+}
+EXPORT_SYMBOL_GPL(xa_delete_node);	/* For the benefit of the test suite */
+
 /**
  * xa_destroy() - Free all internal data structures.
  * @xa: XArray.

mm/workingset.c

@@ -519,12 +519,11 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
 					  void *arg) __must_hold(lru_lock)
 {
 	struct xa_node *node = container_of(item, struct xa_node, private_list);
-	XA_STATE(xas, node->array, 0);
 	struct address_space *mapping;
 	int ret;
 
 	/*
-	 * Page cache insertions and deletions synchroneously maintain
+	 * Page cache insertions and deletions synchronously maintain
 	 * the shadow node LRU under the i_pages lock and the
 	 * lru_lock.  Because the page cache tree is emptied before
 	 * the inode can be destroyed, holding the lru_lock pins any
@@ -559,15 +558,7 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
 	if (WARN_ON_ONCE(node->count != node->nr_values))
 		goto out_invalid;
 	mapping->nrexceptional -= node->nr_values;
-	xas.xa_node = xa_parent_locked(&mapping->i_pages, node);
-	xas.xa_offset = node->offset;
-	xas.xa_shift = node->shift + XA_CHUNK_SHIFT;
-	xas_set_update(&xas, workingset_update_node);
-	/*
-	 * We could store a shadow entry here which was the minimum of the
-	 * shadow entries we were tracking ...
-	 */
-	xas_store(&xas, NULL);
+	xa_delete_node(node, workingset_update_node);
 	__inc_lruvec_slab_state(node, WORKINGSET_NODERECLAIM);
 
 out_invalid: