[PATCH v3 08/20] zswap: prepare zswap for swap virtualization

[Nhat Pham <nphamcs@gmail.com>]

The zswap tree code, specifically the range partition logic, can no
longer easily be reused for the new virtual swap space design. Use a
simple unified zswap tree in the new implementation for now.

Signed-off-by: Nhat Pham <nphamcs@gmail.com>
---
 include/linux/zswap.h |  7 -----
 mm/swapfile.c         |  9 +-----
 mm/zswap.c            | 69 +++++++------------------------------------
 3 files changed, 11 insertions(+), 74 deletions(-)

diff --git a/include/linux/zswap.h b/include/linux/zswap.h
index 30c193a1207e1..1a04caf283dc8 100644
--- a/include/linux/zswap.h
+++ b/include/linux/zswap.h
@@ -28,8 +28,6 @@ unsigned long zswap_total_pages(void);
 bool zswap_store(struct folio *folio);
 int zswap_load(struct folio *folio);
 void zswap_invalidate(swp_entry_t swp);
-int zswap_swapon(int type, unsigned long nr_pages);
-void zswap_swapoff(int type);
 void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg);
 void zswap_lruvec_state_init(struct lruvec *lruvec);
 void zswap_folio_swapin(struct folio *folio);
@@ -50,11 +48,6 @@ static inline int zswap_load(struct folio *folio)
 }
 
 static inline void zswap_invalidate(swp_entry_t swp) {}
-static inline int zswap_swapon(int type, unsigned long nr_pages)
-{
-	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) {}
 static inline void zswap_folio_swapin(struct folio *folio) {}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4b4126d4e2769..3f70df488c1da 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2970,7 +2970,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	spin_unlock(&p->lock);
 	spin_unlock(&swap_lock);
 	arch_swap_invalidate_area(p->type);
-	zswap_swapoff(p->type);
 	mutex_unlock(&swapon_mutex);
 	kfree(p->global_cluster);
 	p->global_cluster = NULL;
@@ -3613,10 +3612,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		}
 	}
 
-	error = zswap_swapon(si->type, maxpages);
-	if (error)
-		goto bad_swap_unlock_inode;
-
 	/*
 	 * Flush any pending IO and dirty mappings before we start using this
 	 * swap device.
@@ -3625,7 +3620,7 @@ 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_zswap;
+		goto bad_swap_unlock_inode;
 	}
 
 	mutex_lock(&swapon_mutex);
@@ -3648,8 +3643,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 
 	error = 0;
 	goto out;
-free_swap_zswap:
-	zswap_swapoff(si->type);
 bad_swap_unlock_inode:
 	inode_unlock(inode);
 bad_swap:
diff --git a/mm/zswap.c b/mm/zswap.c
index a5a3f068bd1a6..f7313261673ff 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -197,8 +197,6 @@ struct zswap_entry {
 	struct list_head lru;
 };
 
-static struct xarray *zswap_trees[MAX_SWAPFILES];
-static unsigned int nr_zswap_trees[MAX_SWAPFILES];
 
 /* RCU-protected iteration */
 static LIST_HEAD(zswap_pools);
@@ -225,45 +223,35 @@ static bool zswap_has_pool;
 * helpers and fwd declarations
 **********************************/
 
-/* One swap address space for each 64M swap space */
-#define ZSWAP_ADDRESS_SPACE_SHIFT 14
-#define ZSWAP_ADDRESS_SPACE_PAGES (1 << ZSWAP_ADDRESS_SPACE_SHIFT)
-static inline struct xarray *swap_zswap_tree(swp_entry_t swp)
-{
-	return &zswap_trees[swp_type(swp)][swp_offset(swp)
-		>> ZSWAP_ADDRESS_SPACE_SHIFT];
-}
+static DEFINE_XARRAY(zswap_tree);
+
+#define zswap_tree_index(entry)	(entry.val)
 
 static inline void *zswap_entry_store(swp_entry_t swpentry,
 		struct zswap_entry *entry)
 {
-	struct xarray *tree = swap_zswap_tree(swpentry);
-	pgoff_t offset = swp_offset(swpentry);
+	pgoff_t offset = zswap_tree_index(swpentry);
 
-	return xa_store(tree, offset, entry, GFP_KERNEL);
+	return xa_store(&zswap_tree, offset, entry, GFP_KERNEL);
 }
 
 static inline void *zswap_entry_load(swp_entry_t swpentry)
 {
-	struct xarray *tree = swap_zswap_tree(swpentry);
-	pgoff_t offset = swp_offset(swpentry);
+	pgoff_t offset = zswap_tree_index(swpentry);
 
-	return xa_load(tree, offset);
+	return xa_load(&zswap_tree, offset);
 }
 
 static inline void *zswap_entry_erase(swp_entry_t swpentry)
 {
-	struct xarray *tree = swap_zswap_tree(swpentry);
-	pgoff_t offset = swp_offset(swpentry);
+	pgoff_t offset = zswap_tree_index(swpentry);
 
-	return xa_erase(tree, offset);
+	return xa_erase(&zswap_tree, offset);
 }
 
 static inline bool zswap_empty(swp_entry_t swpentry)
 {
-	struct xarray *tree = swap_zswap_tree(swpentry);
-
-	return xa_empty(tree);
+	return xa_empty(&zswap_tree);
 }
 
 #define zswap_pool_debug(msg, p)			\
@@ -1691,43 +1679,6 @@ void zswap_invalidate(swp_entry_t swp)
 		zswap_entry_free(entry);
 }
 
-int zswap_swapon(int type, unsigned long nr_pages)
-{
-	struct xarray *trees, *tree;
-	unsigned int nr, i;
-
-	nr = DIV_ROUND_UP(nr_pages, ZSWAP_ADDRESS_SPACE_PAGES);
-	trees = kvcalloc(nr, sizeof(*tree), GFP_KERNEL);
-	if (!trees) {
-		pr_err("alloc failed, zswap disabled for swap type %d\n", type);
-		return -ENOMEM;
-	}
-
-	for (i = 0; i < nr; i++)
-		xa_init(trees + i);
-
-	nr_zswap_trees[type] = nr;
-	zswap_trees[type] = trees;
-	return 0;
-}
-
-void zswap_swapoff(int type)
-{
-	struct xarray *trees = zswap_trees[type];
-	unsigned int i;
-
-	if (!trees)
-		return;
-
-	/* try_to_unuse() invalidated all the entries already */
-	for (i = 0; i < nr_zswap_trees[type]; i++)
-		WARN_ON_ONCE(!xa_empty(trees + i));
-
-	kvfree(trees);
-	nr_zswap_trees[type] = 0;
-	zswap_trees[type] = NULL;
-}
-
 /*********************************
 * debugfs functions
 **********************************/
-- 
2.47.3