linux-kernel - Re: [PATCH/RFC] VFS: don't keep disconnected dentries on d

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Date:   Wed, 20 Dec 2017 16:57:28 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     NeilBrown <neilb@...e.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH/RFC] VFS: don't keep disconnected dentries on d_anon

On Wed, Dec 20, 2017 at 2:45 PM, NeilBrown <neilb@...e.com> wrote:
>
> We could just leave the code unchanged, but apart from that being
> potentially confusing, the (unfair) bit-spin-lock which protects
> s_anon can become a bottle neck when lots of disconnected dentries are
> being created.
>
> So this patch renames s_anon to s_roots, and stops storing
> disconnected dentries on the list.  Only dentries obtained with
> d_obtain_root() are now stored on this list.  There are many fewer of
> these (only NFS and NILFS2 use the call, and only during filesystem
> mount) so contention on the bit-lock will not be a problem.

Thanks, Neil. This is much nicer than the magical special case patch
for s_anon bitlock.

Al, I'm going to assume I'll get this through your vfs tree (with
whatever edits from the comments people made).

                Linus