Re: [PATCH] Re: Possible FS race condition between iterate_dir and d_alloc_parallel

[Al Viro <viro@zeniv.linux.org.uk>]

On Wed, Sep 25, 2019 at 02:59:47PM +0300, Amir Goldstein wrote:
> On Mon, Sep 23, 2019 at 5:34 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > FWIW, #next.dcache has the straight conversion to hlist.
> 
> Note that this:
> @@ -108,8 +108,8 @@ struct dentry {
>                 struct list_head d_lru;         /* LRU list */
>                 wait_queue_head_t *d_wait;      /* in-lookup ones only */
>         };
> -       struct list_head d_child;       /* child of parent list */
> -       struct list_head d_subdirs;     /* our children */
> +       struct hlist_node d_sibling;    /* child of parent list */
> +       struct hlist_head d_children;   /* our children */
> 
> Changes the 'standard' struct dentry size from 192 to 184.
> 
> Does that matter for cache line alignment?
> 
> Should struct dentry be ____cacheline_aligned?

*shrug*

DNAME_INLINE_LEN would need to be adjusted; it's just that I think
it would make a lot of sense to represent cursors not by dentries and
hang those on an additional hlist_head in dentry...