[PATCH 03/15] mm: introduce anon_vma_tree_t for multiple anon_vma topologies

[tao]

Prepare for upcoming ANON_VMA_LAZY support and RCU-based lockless rmap
traversal by clearly separating anon_vma topology handling from the
anon_rmap semantics.

Prepare for supporting multiple anon_vma topologies by introducing
lightweight abstractions used by the VMA and rmap code.

Introduce anon_vma_tree_t as the type stored in vma->anon_vma:

    typedef unsigned long anon_vma_tree_t;

It represents a tagged pointer encoding a reference to the anon_vma
topology. The low bits are reserved as type tags to distinguish
different implementations (e.g. regular anon_vma and lazy anon_vma).
This keeps the VMA representation compact while allowing the topology
to evolve without changing the VMA layout.

Signed-off-by: tao <tao.wangtao@xxxxxxxxx>
---
 include/linux/mm_types.h |  3 +++
 mm/internal.h            | 54 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index a308e2c23b82..5f4961ea1572 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -917,6 +917,9 @@ struct vm_area_desc {
 	struct mmap_action action;
 };
 
+/* Tagged pointer stored in vma->anon_vma. Low bits encode anon_vma type. */
+typedef unsigned long anon_vma_tree_t;
+
 /*
  * This struct describes a virtual memory area. There is one of these
  * per VM-area/task. A VM area is any part of the process virtual memory
diff --git a/mm/internal.h b/mm/internal.h
index 5a2ddcf68e0b..76544ad44ff0 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -246,6 +246,60 @@ static inline void anon_vma_unlock_read(struct anon_vma *anon_vma)
 	up_read(&anon_vma->root->rwsem);
 }
 
+/* anon_vma_tree_t APIs */
+
+static inline anon_vma_tree_t make_anon_vma_tree(struct anon_vma *anon_vma)
+{
+	return (anon_vma_tree_t)anon_vma;
+}
+
+static inline struct anon_vma *anon_vma_tree_anon_vma(anon_vma_tree_t anon_tree)
+{
+	return (struct anon_vma *)anon_tree;
+}
+
+static inline void anon_vma_tree_lock_write(anon_vma_tree_t anon_tree)
+{
+	struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree);
+
+	anon_vma_lock_write(anon_vma);
+}
+
+static inline int anon_vma_tree_trylock_write(anon_vma_tree_t anon_tree)
+{
+	struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree);
+
+	return anon_vma_trylock_write(anon_vma);
+}
+
+static inline void anon_vma_tree_unlock_write(anon_vma_tree_t anon_tree)
+{
+	struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree);
+
+	anon_vma_unlock_write(anon_vma);
+}
+
+static inline void anon_vma_tree_lock_read(anon_vma_tree_t anon_tree)
+{
+	struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree);
+
+	anon_vma_lock_read(anon_vma);
+}
+
+static inline int anon_vma_tree_trylock_read(anon_vma_tree_t anon_tree)
+{
+	struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree);
+
+	return anon_vma_trylock_read(anon_vma);
+}
+
+static inline void anon_vma_tree_unlock_read(anon_vma_tree_t anon_tree)
+{
+	struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree);
+
+	anon_vma_unlock_read(anon_vma);
+}
+
 struct anon_vma *folio_get_anon_vma(const struct folio *folio);
 
 /* Operations which modify VMAs. */
-- 
2.17.1