[PATCH v5 3/5] writeback: fix build problems of "writeback: support retrieving per group debug writeback stats of bdi"

[Kemeng Shi <shikemeng@huaweicloud.com>]

Fix two build problems:
1. implicit declaration of function 'cgroup_ino'.
2. unused variable 'stats'.

After this fix, No build problem is found when CGROUPS is disabled.
The wb_stats could be successfully retrieved when CGROUP_WRITEBACK is
disabled:
cat wb_stats
WbCgIno:                    1
WbWriteback:                0 kB
WbReclaimable:         685440 kB
WbDirtyThresh:      195530960 kB
WbDirtied:             691488 kB
WbWritten:               6048 kB
WbWriteBandwidth:      102400 kBps
b_dirty:                    2
b_io:                       0
b_more_io:                  0
b_dirty_time:               0
state:                      5

cat wb_stats
WbCgIno:                    1
WbWriteback:                0 kB
WbReclaimable:         818944 kB
WbDirtyThresh:      195527484 kB
WbDirtied:             824992 kB
WbWritten:               6048 kB
WbWriteBandwidth:      102400 kBps
b_dirty:                    2
b_io:                       0
b_more_io:                  0
b_dirty_time:               0
state:                      5

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 mm/backing-dev.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 6ecd11bdce6e..e61bbb1bd622 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -172,7 +172,11 @@ static void wb_stats_show(struct seq_file *m, struct bdi_writeback *wb,
 		   "b_more_io:         %10lu\n"
 		   "b_dirty_time:      %10lu\n"
 		   "state:             %10lx\n\n",
+#ifdef CONFIG_CGROUP_WRITEBACK
 		   cgroup_ino(wb->memcg_css->cgroup),
+#else
+		   1ul,
+#endif
 		   K(stats->nr_writeback),
 		   K(stats->nr_reclaimable),
 		   K(stats->wb_thresh),
@@ -192,7 +196,6 @@ static int cgwb_debug_stats_show(struct seq_file *m, void *v)
 	unsigned long background_thresh;
 	unsigned long dirty_thresh;
 	struct bdi_writeback *wb;
-	struct wb_stats stats;
 
 	global_dirty_limits(&background_thresh, &dirty_thresh);
 
-- 
2.30.0