Re: [PATCH 01/10] VFS: support parallel updates in the one directory.

[Al Viro]

On Fri, Aug 26, 2022 at 12:06:55PM -0700, Linus Torvalds wrote:

> Because right now I think the main reason we cannot move the lock into
> the filesystem is literally that we've made the lock cover not just
> the filesystem part, but the "lookup and create dentry" part too.

How about rename loop prevention?  mount vs. rmdir?  d_splice_alias()
fun on tree reconnects?

> But once you have that "DCACHE_PAR_LOOKUP" bit and the
> d_alloc_parallel() logic to serialize a _particular_ dentry being
> created (as opposed to serializing all the sleeping ops to that
> directly), I really think we should strive to move the locking - that
> no longer helps the VFS dcache layer - closer to the filesystem call
> and eventually into it.

See above.