Re: [PATCH v6 1/3] writeback: clear the old wb's dirty IO state after switching inodes

[Jan Kara]

On Fri 02-10-26 21:40:45, Liz Fong-Jones wrote:
> Switching a dirty inode to another wb can leave WB_has_dirty_io set on
> the old one. inode_do_switch_wbs() moves the inode onto new_wb->b_dirty
> through inode_io_list_move_locked(), which only updates new_wb, and
> nothing calls wb_io_lists_depopulated() on old_wb. A live wb clears the
> bit on its next dirty to clean transition, but a wb that gets no more
> inodes, such as a dying one, is freed with its avg_write_bandwidth still
> in bdi->tot_write_bandwidth, which wb_split_bdi_pages() and
> wb_min_max_ratio() divide by.
> 
> Call wb_io_lists_depopulated(old_wb) after the switch loop in
> process_inode_switch_wbs(), while old_wb->list_lock is still held.
> 
> Test: after the last patch in this series switched a replaced wb's dirty
> inodes away, BdiWriteBandwidth stayed at 411700 and 407820 kBps with no
> writers and b_dirty, b_io and b_more_io all empty; with this patch it
> read 0, in 3 of 3 runs.
> 
> Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
> Assisted-by: Claude:claude-opus-5-5 checkpatch sparse
> Assisted-by: Claude:claude-fable-5-1
> Acked-by: Tejun Heo <tj@xxxxxxxxxx>
> Signed-off-by: Liz Fong-Jones <lizf@xxxxxxxxxxxx>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/fs-writeback.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index d26b2cf05283..050d507aa554 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -566,6 +566,12 @@ static void process_inode_switch_wbs(struct bdi_writeback *new_wb,
>  		}
>  	}
>  
> +	/*
> +	 * inode_do_switch_wbs() only updates @new_wb's dirty IO state.  Clear
> +	 * @old_wb's if its IO lists are now empty.
> +	 */
> +	wb_io_lists_depopulated(old_wb);
> +
>  	spin_unlock(&new_wb->list_lock);
>  	spin_unlock(&old_wb->list_lock);
>  
> 
> -- 
> 2.53.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR