1 files changed, 33 insertions, 0 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
index f3a32a06a950..d1f5b8fa52fc 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -235,6 +235,39 @@ void swap_cache_del_folio(struct folio *folio)
 }
 
 /**
+ * __swap_cache_replace_folio - Replace a folio in the swap cache.
+ * @old: The old folio to be replaced.
+ * @new: The new folio.
+ *
+ * Replace an existing folio in the swap cache with a new folio. The
+ * caller is responsible for setting up the new folio's flag and swap
+ * entries. Replacement will take the new folio's swap entry value as
+ * the starting offset to override all slots covered by the new folio.
+ *
+ * Context: Caller must ensure both folios are locked, also lock the
+ * swap address_space that holds the old folio to avoid races.
+ */
+void __swap_cache_replace_folio(struct folio *old, struct folio *new)
+{
+	swp_entry_t entry = new->swap;
+	unsigned long nr_pages = folio_nr_pages(new);
+	unsigned long offset = swap_cache_index(entry);
+	unsigned long end = offset + nr_pages;
+
+	XA_STATE(xas, &swap_address_space(entry)->i_pages, offset);
+
+	VM_WARN_ON_ONCE(!folio_test_swapcache(old) || !folio_test_swapcache(new));
+	VM_WARN_ON_ONCE(!folio_test_locked(old) || !folio_test_locked(new));
+	VM_WARN_ON_ONCE(!entry.val);
+
+	/* Swap cache still stores N entries instead of a high-order entry */
+	do {
+		WARN_ON_ONCE(xas_store(&xas, new) != old);
+		xas_next(&xas);
+	} while (++offset < end);
+}
+
+/**
  * swap_cache_clear_shadow - Clears a set of shadows in the swap cache.
  * @type: Indicates the swap device.
  * @begin: Beginning offset of the range.