maple_tree: introduce mas_wr_prealloc_setup()

Introduce a helper function, mas_wr_prealoc_setup(), that will set up a
maple write state in order to start a walk of a maple tree.

Link: https://lkml.kernel.org/r/20240814161944.55347-3-sidhartha.kumar@oracle.comSigned-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -5399,6 +5399,13 @@ static void mas_wr_store_setup(struct ma_wr_state *wr_mas)
 	mas_reset(wr_mas->mas);
 }
 
+static inline void mas_wr_prealloc_setup(struct ma_wr_state *wr_mas)
+{
+	struct ma_state *mas = wr_mas->mas;
+
+	mas_wr_store_setup(wr_mas);
+	wr_mas->content = mas_start(mas);
+}
 /* Interface */
 
 /**
@@ -5509,8 +5516,7 @@ int mas_preallocate(struct ma_state *mas, void *entry, gfp_t gfp)
 	if (unlikely(!mas->index && mas->last == ULONG_MAX))
 		goto ask_now;
 
-	mas_wr_store_setup(&wr_mas);
-	wr_mas.content = mas_start(mas);
+	mas_wr_prealloc_setup(&wr_mas);
 	/* Root expand */
 	if (unlikely(mas_is_none(mas) || mas_is_ptr(mas)))
 		goto ask_now;