[PATCH v2 1/2] mm/zswap: make sure each swapfile always have zswap rb-tree

[Chengming Zhou]

Not all zswap interfaces can handle the absence of the zswap rb-tree,
actually only zswap_store() has handled it for now.

To make things simple, we make sure each swapfile always have the
zswap rb-tree prepared before being enabled and used. The preparation
is unlikely to fail in practice, this patch just make it explicit.

Acked-by: Nhat Pham <nphamcs@xxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
---
 include/linux/zswap.h |  7 +++++--
 mm/swapfile.c         | 10 +++++++---
 mm/zswap.c            |  7 ++++---
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/include/linux/zswap.h b/include/linux/zswap.h
index 0b709f5bc65f..eca388229d9a 100644
--- a/include/linux/zswap.h
+++ b/include/linux/zswap.h
@@ -30,7 +30,7 @@ struct zswap_lruvec_state {
 bool zswap_store(struct folio *folio);
 bool zswap_load(struct folio *folio);
 void zswap_invalidate(int type, pgoff_t offset);
-void zswap_swapon(int type);
+int zswap_swapon(int type);
 void zswap_swapoff(int type);
 void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg);
 void zswap_lruvec_state_init(struct lruvec *lruvec);
@@ -51,7 +51,10 @@ static inline bool zswap_load(struct folio *folio)
 }
 
 static inline void zswap_invalidate(int type, pgoff_t offset) {}
-static inline void zswap_swapon(int type) {}
+static inline int zswap_swapon(int type)
+{
+	return 0;
+}
 static inline void zswap_swapoff(int type) {}
 static inline void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) {}
 static inline void zswap_lruvec_state_init(struct lruvec *lruvec) {}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 3eec686484ef..6c53ea06626b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2347,8 +2347,6 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
 				unsigned char *swap_map,
 				struct swap_cluster_info *cluster_info)
 {
-	zswap_swapon(p->type);
-
 	spin_lock(&swap_lock);
 	spin_lock(&p->lock);
 	setup_swap_info(p, prio, swap_map, cluster_info);
@@ -3166,6 +3164,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (error)
 		goto bad_swap_unlock_inode;
 
+	error = zswap_swapon(p->type);
+	if (error)
+		goto free_swap_address_space;
+
 	/*
 	 * Flush any pending IO and dirty mappings before we start using this
 	 * swap device.
@@ -3174,7 +3176,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	error = inode_drain_writes(inode);
 	if (error) {
 		inode->i_flags &= ~S_SWAPFILE;
-		goto free_swap_address_space;
+		goto free_swap_zswap;
 	}
 
 	mutex_lock(&swapon_mutex);
@@ -3198,6 +3200,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 
 	error = 0;
 	goto out;
+free_swap_zswap:
+	zswap_swapoff(p->type);
 free_swap_address_space:
 	exit_swap_address_space(p->type);
 bad_swap_unlock_inode:
diff --git a/mm/zswap.c b/mm/zswap.c
index ca25b676048e..d88faea85978 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1519,7 +1519,7 @@ bool zswap_store(struct folio *folio)
 	if (folio_test_large(folio))
 		return false;
 
-	if (!zswap_enabled || !tree)
+	if (!zswap_enabled)
 		return false;
 
 	/*
@@ -1772,19 +1772,20 @@ void zswap_invalidate(int type, pgoff_t offset)
 	spin_unlock(&tree->lock);
 }
 
-void zswap_swapon(int type)
+int zswap_swapon(int type)
 {
 	struct zswap_tree *tree;
 
 	tree = kzalloc(sizeof(*tree), GFP_KERNEL);
 	if (!tree) {
 		pr_err("alloc failed, zswap disabled for swap type %d\n", type);
-		return;
+		return -ENOMEM;
 	}
 
 	tree->rbroot = RB_ROOT;
 	spin_lock_init(&tree->lock);
 	zswap_trees[type] = tree;
+	return 0;
 }
 
 void zswap_swapoff(int type)

-- 
b4 0.10.1