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

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Message-ID: <20171221054000.GX21978@ZenIV.linux.org.uk>
Date:   Thu, 21 Dec 2017 05:40:00 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     NeilBrown <neilb@...e.com>,
        "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 04:57:28PM -0800, Linus Torvalds wrote:
> 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).

*nod*

I've got sidetracked digging through the Lustre mess with dcache (revalidation
stuff, again), will finish once I get some sleep.  In any case, I like that
variant; it's definitely going to be applied.