On Fri 26-07-24 11:05:25, 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>
> Suggested-by: Jan Kara <jack@xxxxxxx>
Looks good! Thanks! Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> Changes since v1:
> - do the check in cgroup_writeback_umount().
> - check the capabilities of bdi.
> ---
> fs/fs-writeback.c | 6 +++++-
> fs/super.c | 2 +-
> include/linux/writeback.h | 4 ++--
> 3 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 92a5b8283528..09facd4356d9 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -1140,8 +1140,12 @@ int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,
> * rare occurrences and synchronize_rcu() can take a while, perform
> * flushing iff wb switches are in flight.
> */
> -void cgroup_writeback_umount(void)
> +void cgroup_writeback_umount(struct super_block *sb)
> {
> +
> + if (!(sb->s_bdi->capabilities & BDI_CAP_WRITEBACK))
> + return;
> +
> /*
> * SB_ACTIVE should be reliably cleared before checking
> * isw_nr_in_flight, see generic_shutdown_super().
> diff --git a/fs/super.c b/fs/super.c
> index 095ba793e10c..acc16450da0e 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -621,7 +621,7 @@ void generic_shutdown_super(struct super_block *sb)
> sync_filesystem(sb);
> sb->s_flags &= ~SB_ACTIVE;
>
> - cgroup_writeback_umount();
> + cgroup_writeback_umount(sb);
>
> /* Evict all inodes with zero refcount. */
> evict_inodes(sb);
> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> index 112d806ddbe4..d78d3dce4ede 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)
> {
> }
>
> --
> 2.25.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
