On Mon 22-08-16 13:35:02, Josef Bacik wrote:
> Now that we have metadata counters in the VM, we need to provide a way to kick
> writeback on dirty metadata. Introduce super_operations->write_metadata. This
> allows file systems to deal with writing back any dirty metadata we need based
> on the writeback needs of the system. Since there is no inode to key off of we
> need a list in the bdi for dirty super blocks to be added. From there we can
> find any dirty sb's on the bdi we are currently doing writeback on and call into
> their ->write_metadata callback.
>
> Signed-off-by: Josef Bacik <jbacik@xxxxxx>
...
> @@ -1639,11 +1664,38 @@ static long __writeback_inodes_wb(struct bdi_writeback *wb,
>
> /* refer to the same tests at the end of writeback_sb_inodes */
> if (wrote) {
> - if (time_is_before_jiffies(start_time + HZ / 10UL))
> - break;
> - if (work->nr_pages <= 0)
> + if (time_is_before_jiffies(start_time + HZ / 10UL) ||
> + work->nr_pages <= 0) {
> + done = true;
> break;
> + }
> + }
> + }
> +
> + if (!done && wb_stat(wb, WB_METADATA_DIRTY)) {
> + LIST_HEAD(list);
> +
> + spin_unlock(&wb->list_lock);
> + spin_lock(&wb->bdi->sb_list_lock);
> + list_splice_init(&wb->bdi->dirty_sb_list, &list);
> + while (!list_empty(&list)) {
> + struct super_block *sb;
> +
> + sb = list_first_entry(&list, struct super_block,
> + s_bdi_list);
> + list_move_tail(&sb->s_bdi_list,
> + &wb->bdi->dirty_sb_list);
> + if (!sb->s_op->write_metadata)
> + continue;
> + if (!trylock_super(sb))
> + continue;
> + spin_unlock(&wb->bdi->sb_list_lock);
> + wrote += writeback_sb_metadata(sb, wb, work);
> + spin_lock(&wb->bdi->sb_list_lock);
> + up_read(&sb->s_umount);
> }
> + spin_unlock(&wb->bdi->sb_list_lock);
> + spin_lock(&wb->list_lock);
> }
> /* Leave any unwritten inodes on b_io */
> return wrote;
So this will hook metadata writeback into the periodic writeback but when
work->sb is set, metadata won't be written because in that case we call
writeback_sb_inodes() directly. So you need to call writeback_sb_metadata()
from wb_writeback() in that case as well.
...
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index f3f0b4c8..c063ac6 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1430,6 +1430,8 @@ struct super_block {
>
> spinlock_t s_inode_wblist_lock;
> struct list_head s_inodes_wb; /* writeback inodes */
> +
> + struct list_head s_bdi_list;
Maybe call this s_bdi_dirty_list?
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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