ftl: cache unmapped translations

include/ftl.h

@@ -32,6 +32,7 @@ struct ftl_map {
 };
 
 #define FTL_CACHED_VA BIT(0)
+#define FTL_UNMAPPED  BIT(1)
 
 #define FTL_MAX_ATTEMPTS 8
 

source/ftl/map.c

@@ -382,8 +382,15 @@ int trace_path(struct ftl_map *map, struct ftl_page_desc *new_page_desc,
 	uint8_t depth = 0;
 	uint32_t upage = map->root;
 
-	if ((map->flags & FTL_CACHED_VA) && map->last_va == va)
-		return map->last_pa;
+	if ((map->flags & FTL_CACHED_VA) && map->last_va == va) {
+		if (map->flags & FTL_UNMAPPED)
+			return -1;
+
+		if (page)
+			*page = map->last_pa;
+
+		return 0;
+	}
 
 	if (new_page_desc)
 		new_page_desc->va = va;
@@ -421,6 +428,7 @@ int trace_path(struct ftl_map *map, struct ftl_page_desc *new_page_desc,
 		*page = upage;
 
 	map->flags |= FTL_CACHED_VA;
+	map->flags &= ~FTL_UNMAPPED;
 	map->last_va = va;
 	map->last_pa = upage;
 
@@ -433,5 +441,8 @@ err_not_found:
 		}
 	}
 
+	map->flags |= FTL_CACHED_VA | FTL_UNMAPPED;
+	map->last_va = va;
+
 	return -ERR_NOT_FOUND;
 }