[PATCH v3 4/4] mm/zsmalloc: document free_zspage helper variants

[Wenchao Hao <haowenchao22@gmail.com>]

From: Wenchao Hao <haowenchao@xiaomi.com>

After splitting __free_zspage() into a lockless core and a wrapper that
does the class-stat bookkeeping, three similarly-named helpers coexist:
free_zspage / __free_zspage / __free_zspage_lockless.

Add a comment block above them describing what each does and where it
is used, so the names are not easy to confuse.

No functional change.

Suggested-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Wenchao Hao <haowenchao@xiaomi.com>
---
 mm/zsmalloc.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 2ecdf79cea03..9f588b63ec0d 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -856,6 +856,21 @@ static int trylock_zspage(struct zspage *zspage)
 	return 0;
 }
 
+/*
+ * Three free helpers, kept apart here:
+ *
+ * __free_zspage_lockless(): bare core; walks zpdescs and returns pages
+ *   to the buddy allocator.  Caller owns all zpdesc locks and has
+ *   removed the zspage from its class list.  Used by zs_free() outside
+ *   class->lock so the buddy-side work does not stall the class.
+ *
+ * __free_zspage(): __free_zspage_lockless() + per-class accounting,
+ *   under class->lock.  Used by async_free_zspage().
+ *
+ * free_zspage(): full wrapper - trylock zpdescs, remove from class
+ *   list, call __free_zspage(); kicks deferred free on contention.
+ *   Used by compaction.
+ */
 static inline void __free_zspage_lockless(struct zs_pool *pool, struct zspage *zspage)
 {
 	struct zpdesc *zpdesc, *next;
-- 
2.34.1