On 2024/7/25 16:42, Jan Kara wrote: > On Thu 25-07-24 10:39:58, Haifeng Xu wrote: >> 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 <haifeng.xu@xxxxxxxxxx> >> --- >> fs/super.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/fs/super.c b/fs/super.c >> index 095ba793e10c..f846f853e957 100644 >> --- a/fs/super.c >> +++ b/fs/super.c >> @@ -621,7 +621,8 @@ void generic_shutdown_super(struct super_block *sb) >> sync_filesystem(sb); >> sb->s_flags &= ~SB_ACTIVE; >> >> - cgroup_writeback_umount(); >> + if (sb->s_bdi != &noop_backing_dev_info) >> + cgroup_writeback_umount(); > > So a more obvious check would be: > > if (sb->s_bdi->capabilities & BDI_CAP_WRITEBACK) > > even better would be if we'd pass 'sb' into cgroup_writeback_umount() and > that function would do this check inside so that callers don't have to > bother... I know there is only one caller so this is not a huge deal but > still I'd find it cleaner that way. > > Honza > Yes, Thanks for you suggestions!
