Re: [PATCH 2/1] fs: call fsnotify_sb_delete after evict_inodes

[Jan Kara <jack@suse.cz>]

On Wed 16-10-19 12:11:24, Eric Sandeen wrote:
> When a filesystem is unmounted, we currently call fsnotify_sb_delete()
> before evict_inodes(), which means that fsnotify_unmount_inodes()
> must iterate over all inodes on the superblock, even though it will
> only act on inodes with a refcount.  This is inefficient and can lead
> to livelocks as it iterates over many unrefcounted inodes.
> 
> However, since fsnotify_sb_delete() and evict_inodes() are working
> on orthogonal sets of inodes (fsnotify_sb_delete() only cares about nonzero
> refcount, and evict_inodes() only cares about zero refcount), we can swap
> the order of the calls.  The fsnotify call will then have a much smaller
> list to walk (any refcounted inodes).
> 
> This should speed things up overall, and avoid livelocks in 
> fsnotify_unmount_inodes().
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>

Thanks for the patch. It looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

> ---
> 
> I just did basic sanity testing here, but AFAIK there is no *notify
> test suite, so I'm not sure how to really give this a workout.

LTP has quite a few tests for inotify & fanotify.

								Honza

> diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
> index ac9eb273e28c..426f03b6e660 100644
> --- a/fs/notify/fsnotify.c
> +++ b/fs/notify/fsnotify.c
> @@ -57,6 +57,10 @@ static void fsnotify_unmount_inodes(struct super_block *sb)
>  		 * doing an __iget/iput with SB_ACTIVE clear would actually
>  		 * evict all inodes with zero i_count from icache which is
>  		 * unnecessarily violent and may in fact be illegal to do.
> +		 *
> +		 * However, we should have been called /after/ evict_inodes
> +		 * removed all zero refcount inodes, in any case.  Test to
> +		 * be sure.
>  		 */
>  		if (!atomic_read(&inode->i_count)) {
>  			spin_unlock(&inode->i_lock);
> diff --git a/fs/super.c b/fs/super.c
> index cfadab2cbf35..cd352530eca9 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -448,10 +448,12 @@ void generic_shutdown_super(struct super_block *sb)
>  		sync_filesystem(sb);
>  		sb->s_flags &= ~SB_ACTIVE;
>  
> -		fsnotify_sb_delete(sb);
>  		cgroup_writeback_umount();
>  
> +		/* evict all inodes with zero refcount */
>  		evict_inodes(sb);
> +		/* only nonzero refcount inodes can have marks */
> +		fsnotify_sb_delete(sb);
>  
>  		if (sb->s_dio_done_wq) {
>  			destroy_workqueue(sb->s_dio_done_wq);
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR