[PATCH 2/2] mm: zswap: remove unnecessary tree cleanups in zswap_swapoff()

[Yosry Ahmed <yosryahmed@google.com>]

During swapoff, try_to_unuse() makes sure that zswap_invalidate() is
called for all swap entries before zswap_swapoff() is called. This means
that all zswap entries should already be removed from the tree. Simplify
zswap_swapoff() by removing the tree cleanup loop, and leaving an
assertion in its place.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
---
Chengming, Chris, I think this should make the tree split and the xarray
conversion patches simpler (especially the former). If others agree,
both changes can be rebased on top of this.
---
 mm/zswap.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index f8bc9e0892687..9675c3c27f9d1 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1790,17 +1790,12 @@ void zswap_swapon(int type)
 void zswap_swapoff(int type)
 {
 	struct zswap_tree *tree = zswap_trees[type];
-	struct zswap_entry *entry, *n;
 
 	if (!tree)
 		return;
 
-	/* walk the tree and free everything */
-	spin_lock(&tree->lock);
-	rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode)
-		zswap_free_entry(entry);
-	tree->rbroot = RB_ROOT;
-	spin_unlock(&tree->lock);
+	/* try_to_unuse() invalidated all entries already */
+	WARN_ON_ONCE(!RB_EMPTY_ROOT(&tree->rbroot));
 	kfree(tree);
 	zswap_trees[type] = NULL;
 }
-- 
2.43.0.429.g432eaa2c6b-goog