Hello, Josef.
On Tue, Aug 09, 2016 at 03:08:27PM -0400, Josef Bacik wrote:
> Provide a mechanism for file systems to indicate how much dirty metadata they
> are holding. This introduces a few things
>
> 1) Zone stats for dirty metadata, which is the same as the NR_FILE_DIRTY.
> 2) WB stat for dirty metadata. This way we know if we need to try and call
> into
> the file system to write out metadata. This could potentially be used in the
> future to make balancing of dirty pages smarter.
> 3) A super callback to handle writing back dirty metadata.
>
> A future patch will take advantage of this work in btrfs. Thanks,
>
> Signed-off-by: Josef Bacik <jba...@fb.com>
...
> + if (!done && wb_stat(wb, WB_METADATA_DIRTY)) {
> + struct list_head list;
> +
> + spin_unlock(&wb->list_lock);
> + spin_lock(&wb->bdi->sb_list_lock);
> + list_splice_init(&wb->bdi->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(&wb->bdi->sb_list, &sb->s_bdi_list);
It bothers me a bit that sb's can actually be off bdi->sb_list while
sb_list_lock is released. Can we make this explicit? e.g. keep
separate bdi sb list for sb's pending metadata writeout (like b_dirty)
or by just walking the list in a smart way?
> + 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;
> diff --git a/fs/super.c b/fs/super.c
> index c2ff475..940696d 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -215,6 +215,7 @@ static struct super_block *alloc_super(struct
> file_system_type *type, int flags,
> spin_lock_init(&s->s_inode_list_lock);
> INIT_LIST_HEAD(&s->s_inodes_wb);
> spin_lock_init(&s->s_inode_wblist_lock);
> + INIT_LIST_HEAD(&s->s_bdi_list);
I can't find where sb's are actually added to the list. Is that
supposed to happen from specific filesystems? Also, it might make
sense to split up additions of sb_list and stat into separate patches.
Thanks.
--
tejun
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