zsmalloc: move migration destination zspage inuse check

Destination zspage fullness check need to be done after zs_object_copy()
because that's where source and destination zspages fullness change. 
Checking destination zspage fullness before zs_object_copy() may cause
migration to loop through source zspage sub-pages scanning for allocate
objects just to find out at the end that the destination zspage is full.

Link: https://lkml.kernel.org/r/20230624053120.643409-3-senozhatsky@chromium.orgSigned-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org> 
Cc: Alexey Romanov <avromanov@sberdevices.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/zsmalloc.c

@@ -1620,10 +1620,6 @@ static void migrate_zspage(struct zs_pool *pool, struct size_class *class,
 			continue;
 		}
 
-		/* Stop if there is no more space */
-		if (zspage_full(class, get_zspage(d_page)))
-			break;
-
 		used_obj = handle_to_obj(handle);
 		free_obj = obj_malloc(pool, get_zspage(d_page), handle);
 		zs_object_copy(class, free_obj, used_obj);
@@ -1631,6 +1627,10 @@ static void migrate_zspage(struct zs_pool *pool, struct size_class *class,
 		record_obj(handle, free_obj);
 		obj_free(class->size, used_obj);
 
+		/* Stop if there is no more space */
+		if (zspage_full(class, get_zspage(d_page)))
+			break;
+
 		/* Stop if there are no more objects to migrate */
 		if (zspage_empty(get_zspage(s_page)))
 			break;