fs/writeback: wrap cgroup writeback v1 logic

Wrap cgroup writeback v1 logic to prevent build errors without
CONFIG_CGROUPS or CONFIG_CGROUP_WRITEBACK.
Reported-by: Nkbuild test robot <lkp@intel.com>
Cc: Jiufei Xue <jiufei.xue@linux.alibaba.com>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NCaspar Zhang <caspar@linux.alibaba.com>

include/linux/backing-dev.h

@@ -481,6 +481,7 @@ static inline int inode_congested(struct inode *inode, int cong_bits)
 	return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
 }
 
+#ifdef CONFIG_CGROUPS
 static inline void insert_memcg_blkcg_link(struct cgroup_subsys *ss,
 					   struct list_head *tmp_links,
 					   struct css_set *cset)
@@ -500,6 +501,7 @@ static inline void delete_memcg_blkcg_link(struct cgroup_subsys *ss,
 					   struct cgroup_subsys_state *css)
 {
 }
+#endif
 
 #endif	/* CONFIG_CGROUP_WRITEBACK */
 

include/trace/events/writeback.h

@@ -303,6 +303,7 @@ TRACE_EVENT(writeback_bdi_register,
 	)
 );
 
+#ifdef CONFIG_CGROUP_WRITEBACK
 TRACE_EVENT(insert_memcg_blkcg_link,
 	TP_PROTO(struct cgroup_subsys_state *memcg_css,
 		 struct cgroup_subsys_state *blkcg_css,
@@ -323,6 +324,7 @@ TRACE_EVENT(insert_memcg_blkcg_link,
 		  __entry->memcg_ino, __entry->blkcg_ino, __entry->old_blkcg_ino
 	)
 );
+#endif
 
 DECLARE_EVENT_CLASS(wbc_class,
 	TP_PROTO(struct writeback_control *wbc, struct backing_dev_info *bdi),

mm/memcontrol.c

@@ -468,8 +468,12 @@ struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page)
 
 	memcg = page->mem_cgroup;
 
+#ifdef CONFIG_CGROUP_WRITEBACK
 	if (!memcg ||
-	   (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !cgwb_v1))
+	    (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !cgwb_v1))
+#else
+	if (!memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
+#endif
 		memcg = root_mem_cgroup;
 
 	return &memcg->css;
@@ -6370,6 +6374,7 @@ static int __init cgroup_memory(char *s)
 }
 __setup("cgroup.memory=", cgroup_memory);
 
+#ifdef CONFIG_CGROUP_WRITEBACK
 bool cgwb_v1 = false;
 
 static int __init enable_cgroup_writeback_v1(char *s)
@@ -6379,6 +6384,7 @@ static int __init enable_cgroup_writeback_v1(char *s)
 	return 0;
 }
 __setup("cgwb_v1", enable_cgroup_writeback_v1);
+#endif
 
 /*
  * subsys_initcall() for memory controller.