fs: don't flush in-flight wb switches for superblocks without cgroup writeback

When deactivating any type of superblock, it had to wait for the in-flight
wb switches to be completed. wb switches are executed in inode_switch_wbs_work_fn()
which needs to acquire the wb_switch_rwsem and races against sync_inodes_sb().
If there are too much dirty data in the superblock, the waiting time may increase
significantly.

For superblocks without cgroup writeback such as tmpfs, they have nothing to
do with the wb swithes, so the flushing can be avoided.

Signed-off-by: Haifeng Xu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Suggested-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 1a54676d843a..56b85841ae4c 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -217,7 +217,7 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
 			      size_t bytes);
 int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,
 			   enum wb_reason reason, struct wb_completion *done);
-void cgroup_writeback_umount(void);
+void cgroup_writeback_umount(struct super_block *sb);
 bool cleanup_offline_cgwb(struct bdi_writeback *wb);
 
 /**
@@ -324,7 +324,7 @@ static inline void wbc_account_cgroup_owner(struct writeback_control *wbc,
 {
 }
 
-static inline void cgroup_writeback_umount(void)
+static inline void cgroup_writeback_umount(struct super_block *sb)
 {
 }