1 files changed, 130 insertions, 0 deletions
diff --git a/mm/swap_table.h b/mm/swap_table.h
new file mode 100644
index 000000000000..ea244a57a5b7
--- /dev/null
+++ b/mm/swap_table.h
@@ -0,0 +1,130 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _MM_SWAP_TABLE_H
+#define _MM_SWAP_TABLE_H
+
+#include <linux/rcupdate.h>
+#include <linux/atomic.h>
+#include "swap.h"
+
+/* A typical flat array in each cluster as swap table */
+struct swap_table {
+	atomic_long_t entries[SWAPFILE_CLUSTER];
+};
+
+#define SWP_TABLE_USE_PAGE (sizeof(struct swap_table) == PAGE_SIZE)
+
+/*
+ * A swap table entry represents the status of a swap slot on a swap
+ * (physical or virtual) device. The swap table in each cluster is a
+ * 1:1 map of the swap slots in this cluster.
+ *
+ * Each swap table entry could be a pointer (folio), a XA_VALUE
+ * (shadow), or NULL.
+ */
+
+/*
+ * Helpers for casting one type of info into a swap table entry.
+ */
+static inline unsigned long null_to_swp_tb(void)
+{
+	BUILD_BUG_ON(sizeof(unsigned long) != sizeof(atomic_long_t));
+	return 0;
+}
+
+static inline unsigned long folio_to_swp_tb(struct folio *folio)
+{
+	BUILD_BUG_ON(sizeof(unsigned long) != sizeof(void *));
+	return (unsigned long)folio;
+}
+
+static inline unsigned long shadow_swp_to_tb(void *shadow)
+{
+	BUILD_BUG_ON((BITS_PER_XA_VALUE + 1) !=
+		     BITS_PER_BYTE * sizeof(unsigned long));
+	VM_WARN_ON_ONCE(shadow && !xa_is_value(shadow));
+	return (unsigned long)shadow;
+}
+
+/*
+ * Helpers for swap table entry type checking.
+ */
+static inline bool swp_tb_is_null(unsigned long swp_tb)
+{
+	return !swp_tb;
+}
+
+static inline bool swp_tb_is_folio(unsigned long swp_tb)
+{
+	return !xa_is_value((void *)swp_tb) && !swp_tb_is_null(swp_tb);
+}
+
+static inline bool swp_tb_is_shadow(unsigned long swp_tb)
+{
+	return xa_is_value((void *)swp_tb);
+}
+
+/*
+ * Helpers for retrieving info from swap table.
+ */
+static inline struct folio *swp_tb_to_folio(unsigned long swp_tb)
+{
+	VM_WARN_ON(!swp_tb_is_folio(swp_tb));
+	return (void *)swp_tb;
+}
+
+static inline void *swp_tb_to_shadow(unsigned long swp_tb)
+{
+	VM_WARN_ON(!swp_tb_is_shadow(swp_tb));
+	return (void *)swp_tb;
+}
+
+/*
+ * Helpers for accessing or modifying the swap table of a cluster,
+ * the swap cluster must be locked.
+ */
+static inline void __swap_table_set(struct swap_cluster_info *ci,
+				    unsigned int off, unsigned long swp_tb)
+{
+	atomic_long_t *table = rcu_dereference_protected(ci->table, true);
+
+	lockdep_assert_held(&ci->lock);
+	VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
+	atomic_long_set(&table[off], swp_tb);
+}
+
+static inline unsigned long __swap_table_xchg(struct swap_cluster_info *ci,
+					      unsigned int off, unsigned long swp_tb)
+{
+	atomic_long_t *table = rcu_dereference_protected(ci->table, true);
+
+	lockdep_assert_held(&ci->lock);
+	VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
+	/* Ordering is guaranteed by cluster lock, relax */
+	return atomic_long_xchg_relaxed(&table[off], swp_tb);
+}
+
+static inline unsigned long __swap_table_get(struct swap_cluster_info *ci,
+					     unsigned int off)
+{
+	atomic_long_t *table;
+
+	VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
+	table = rcu_dereference_check(ci->table, lockdep_is_held(&ci->lock));
+
+	return atomic_long_read(&table[off]);
+}
+
+static inline unsigned long swap_table_get(struct swap_cluster_info *ci,
+					unsigned int off)
+{
+	atomic_long_t *table;
+	unsigned long swp_tb;
+
+	rcu_read_lock();
+	table = rcu_dereference(ci->table);
+	swp_tb = table ? atomic_long_read(&table[off]) : null_to_swp_tb();
+	rcu_read_unlock();
+
+	return swp_tb;
+}
+#endif