From: Miklos Szeredi <miklos@szeredi.hu>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Ian Kent <raven@themaw.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Tejun Heo <tj@kernel.org>, Eric Sandeen <sandeen@sandeen.net>,
Fox Chen <foxhlchen@gmail.com>,
Brice Goglin <brice.goglin@gmail.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Rick Lindsley <ricklind@linux.vnet.ibm.com>,
David Howells <dhowells@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [REPOST PATCH v4 2/5] kernfs: use VFS negative dentry caching
Date: Thu, 3 Jun 2021 20:06:38 +0200 [thread overview]
Message-ID: <CAJfpegsVxoL8WgQa7hFXAg4RBbA-suaeo5pZ5EE7HDpL0rT03A@mail.gmail.com> (raw)
In-Reply-To: <87czt2q2pl.fsf@disp2133>
On Thu, 3 Jun 2021 at 19:26, Eric W. Biederman <ebiederm@xmission.com> wrote:
>
> Ian Kent <raven@themaw.net> writes:
>
> > If there are many lookups for non-existent paths these negative lookups
> > can lead to a lot of overhead during path walks.
> >
> > The VFS allows dentries to be created as negative and hashed, and caches
> > them so they can be used to reduce the fairly high overhead alloc/free
> > cycle that occurs during these lookups.
> >
> > Signed-off-by: Ian Kent <raven@themaw.net>
> > ---
> > fs/kernfs/dir.c | 55 +++++++++++++++++++++++++++++++++----------------------
> > 1 file changed, 33 insertions(+), 22 deletions(-)
> >
> > diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
> > index 4c69e2af82dac..5151c712f06f5 100644
> > --- a/fs/kernfs/dir.c
> > +++ b/fs/kernfs/dir.c
> > @@ -1037,12 +1037,33 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
> > if (flags & LOOKUP_RCU)
> > return -ECHILD;
> >
> > - /* Always perform fresh lookup for negatives */
> > - if (d_really_is_negative(dentry))
> > - goto out_bad_unlocked;
> > + mutex_lock(&kernfs_mutex);
> >
> > kn = kernfs_dentry_node(dentry);
> > - mutex_lock(&kernfs_mutex);
>
> Why bring kernfs_dentry_node inside the mutex?
>
> The inode lock of the parent should protect negative to positive
> transitions not the kernfs_mutex. So moving the code inside
> the mutex looks unnecessary and confusing.
Except that d_revalidate() may or may not be called with parent lock held.
Thanks,
Miklos
next prev parent reply other threads:[~2021-06-03 18:07 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-28 6:33 [REPOST PATCH v4 0/5] kernfs: proposed locking and concurrency improvement Ian Kent
2021-05-28 6:33 ` [REPOST PATCH v4 1/5] kernfs: move revalidate to be near lookup Ian Kent
2021-06-03 14:50 ` Eric W. Biederman
2021-06-04 2:29 ` Ian Kent
2021-05-28 6:34 ` [REPOST PATCH v4 2/5] kernfs: use VFS negative dentry caching Ian Kent
2021-06-01 12:41 ` Miklos Szeredi
2021-06-02 3:44 ` Ian Kent
2021-06-02 8:58 ` Miklos Szeredi
2021-06-02 10:57 ` Ian Kent
2021-06-03 2:15 ` Ian Kent
2021-06-03 23:57 ` Ian Kent
2021-06-04 1:07 ` Ian Kent
2021-06-03 17:26 ` Eric W. Biederman
2021-06-03 18:06 ` Miklos Szeredi [this message]
2021-06-03 22:02 ` Eric W. Biederman
2021-06-04 3:14 ` Ian Kent
2021-06-04 14:28 ` Eric W. Biederman
2021-06-05 3:19 ` Ian Kent
2021-06-05 20:52 ` Eric W. Biederman
2021-05-28 6:34 ` [REPOST PATCH v4 3/5] kernfs: switch kernfs to use an rwsem Ian Kent
2021-06-01 13:11 ` Miklos Szeredi
2021-06-03 16:59 ` Eric W. Biederman
2021-05-28 6:34 ` [REPOST PATCH v4 4/5] kernfs: use i_lock to protect concurrent inode updates Ian Kent
2021-05-31 14:53 ` [kernfs] 9a658329cd: stress-ng.get.ops_per_sec 191.4% improvement kernel test robot
2021-06-01 13:18 ` [REPOST PATCH v4 4/5] kernfs: use i_lock to protect concurrent inode updates Miklos Szeredi
2021-06-02 5:41 ` Ian Kent
2021-05-28 6:34 ` [REPOST PATCH v4 5/5] kernfs: add kernfs_need_inode_refresh() Ian Kent
2021-05-28 8:56 ` [REPOST PATCH v4 0/5] kernfs: proposed locking and concurrency improvement Greg Kroah-Hartman
2021-05-28 11:56 ` Fox Chen
2021-05-30 4:44 ` Fox Chen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAJfpegsVxoL8WgQa7hFXAg4RBbA-suaeo5pZ5EE7HDpL0rT03A@mail.gmail.com \
--to=miklos@szeredi.hu \
--cc=brice.goglin@gmail.com \
--cc=dhowells@redhat.com \
--cc=ebiederm@xmission.com \
--cc=foxhlchen@gmail.com \
--cc=gregkh@linuxfoundation.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mtosatti@redhat.com \
--cc=raven@themaw.net \
--cc=ricklind@linux.vnet.ibm.com \
--cc=sandeen@sandeen.net \
--cc=tj@kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).