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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Waiman Long <waiman.long@hp.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Ingo Molnar <mingo@kernel.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Jeff Layton <jlayton@redhat.com>,
	Miklos Szeredi <mszeredi@suse.cz>, Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Andi Kleen <andi@firstfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@hp.com>,
	"Norton, Scott J" <scott.norton@hp.com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount
Date: Fri, 30 Aug 2013 14:22:58 -0700	[thread overview]
Message-ID: <CA+55aFz3+Nbn155YeiwT0uBgqyXsAQn4jkT0NHWnE7+OvJbQig@mail.gmail.com> (raw)
In-Reply-To: <52210A55.8010308@hp.com>

On Fri, Aug 30, 2013 at 2:10 PM, Waiman Long <waiman.long@hp.com> wrote:
>
> Actually, prepend_path() was called with rename_lock taken. So d_move()
> couldn't be run at the same time. Am I right?

Al was discussing the case I mentioned: getting rid of that lock
entirely, running it all just under RCU, and then just checking the
rename sequence count around it all and retrying if required.

It would have the advantage of not only not having to get the lock,
but by doing it as an RCU walk, we would avoid all the nasty reference
counting costs too. We wouldn't even need to get refcounts on the
root/pwd entries (which currently cost us quite a bit), since we could
just check the sequence number in "struct fs_struct" too. That also
gets rid of the necessity for the fs->lock spinlock.

You do have to be a bit careful when following the dentry pointers
under RCU (and you cannot just do a "memcpy()" on the name, as Al
points out), but it really doesn't look nasty. It just looks "you have
to be careful".

              Linus

  reply	other threads:[~2013-08-30 21:22 UTC|newest]

Thread overview: 151+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-08-06  3:12 [PATCH v7 0/4] Lockless update of reference count protected by spinlock Waiman Long
2013-08-06  3:12 ` [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount Waiman Long
2013-08-29  1:40   ` Linus Torvalds
2013-08-29  4:44     ` Benjamin Herrenschmidt
2013-08-29  7:00       ` Ingo Molnar
2013-08-29 16:43         ` Linus Torvalds
2013-08-29 19:25           ` Linus Torvalds
2013-08-29 23:42             ` Linus Torvalds
2013-08-30  0:26               ` Benjamin Herrenschmidt
2013-08-30  0:49                 ` Linus Torvalds
2013-08-30  2:06                   ` Michael Neuling
2013-08-30  2:30                     ` Benjamin Herrenschmidt
2013-08-30  2:35                       ` Linus Torvalds
2013-08-30  2:45                         ` Benjamin Herrenschmidt
2013-08-30  2:31                     ` Linus Torvalds
2013-08-30  2:43                       ` Benjamin Herrenschmidt
2013-08-30  7:16                   ` Ingo Molnar
2013-08-30 15:28                     ` Linus Torvalds
2013-08-30  3:12               ` Waiman Long
2013-08-30  3:54                 ` Linus Torvalds
2013-08-30  7:55                   ` Sedat Dilek
2013-08-30  8:10                     ` Sedat Dilek
2013-08-30  9:27                     ` Sedat Dilek
2013-08-30  9:48                       ` Ingo Molnar
2013-08-30  9:56                         ` Sedat Dilek
2013-08-30  9:58                           ` Sedat Dilek
2013-08-30 10:29                             ` Sedat Dilek
2013-08-30 10:36                               ` Peter Zijlstra
2013-08-30 10:44                                 ` Sedat Dilek
2013-08-30 10:46                                   ` Sedat Dilek
2013-08-30 10:52                                   ` Peter Zijlstra
2013-08-30 10:57                                     ` Sedat Dilek
2013-08-30 14:05                                       ` Sedat Dilek
2013-08-30 11:19                                 ` Sedat Dilek
2013-08-30 10:38                               ` Sedat Dilek
2013-08-30 15:34                       ` Linus Torvalds
2013-08-30 15:38                         ` Sedat Dilek
2013-08-30 16:12                           ` Steven Rostedt
2013-08-30 16:16                             ` Sedat Dilek
2013-08-30 18:42                             ` Linus Torvalds
2013-08-30 16:32                           ` Linus Torvalds
2013-08-30 16:37                             ` Sedat Dilek
2013-08-30 16:52                               ` Linus Torvalds
2013-08-30 17:11                                 ` Sedat Dilek
2013-08-30 17:26                                   ` Linus Torvalds
2013-09-01 10:01                                 ` Sedat Dilek
2013-09-01 10:33                                   ` Sedat Dilek
2013-09-01 15:32                                   ` Linus Torvalds
2013-09-01 15:45                                     ` Sedat Dilek
2013-09-01 15:55                                       ` Linus Torvalds
2013-09-02 10:30                                         ` Sedat Dilek
2013-09-02 16:09                                           ` David Ahern
2013-09-01 20:59                                     ` Linus Torvalds
2013-09-01 21:23                                       ` Al Viro
2013-09-01 22:16                                         ` Linus Torvalds
2013-09-01 22:35                                           ` Al Viro
2013-09-01 22:44                                             ` Al Viro
2013-09-01 22:58                                               ` Linus Torvalds
2013-09-01 22:48                                           ` Linus Torvalds
2013-09-01 23:30                                             ` Al Viro
2013-09-02  0:12                                               ` Linus Torvalds
2013-09-02  0:50                                                 ` Linus Torvalds
2013-09-02  7:05                                                   ` Ingo Molnar
2013-09-02 16:44                                                     ` Linus Torvalds
2013-09-03 10:15                                                       ` Ingo Molnar
2013-09-03 15:41                                                         ` Linus Torvalds
2013-09-03 18:34                                                           ` Linus Torvalds
2013-09-03 19:19                                                             ` Ingo Molnar
2013-09-03 21:05                                                               ` Linus Torvalds
2013-09-03 21:13                                                                 ` Linus Torvalds
2013-09-03 21:34                                                                   ` Linus Torvalds
2013-09-03 21:39                                                                     ` Linus Torvalds
2013-09-03 14:08                                                       ` Pavel Machek
2013-09-03 22:37                                     ` Sedat Dilek
2013-09-03 22:55                                       ` Dave Jones
2013-09-03 23:05                                         ` Sedat Dilek
2013-09-03 23:15                                           ` Dave Jones
2013-09-03 23:20                                             ` Sedat Dilek
2013-09-03 23:45                                       ` Sedat Dilek
2013-08-30 18:33                   ` Waiman Long
2013-08-30 18:53                     ` Linus Torvalds
2013-08-30 19:20                       ` Waiman Long
2013-08-30 19:33                         ` Linus Torvalds
2013-08-30 20:15                           ` Waiman Long
2013-08-30 20:43                             ` Linus Torvalds
2013-08-30 20:54                               ` Al Viro
2013-08-30 21:03                                 ` Linus Torvalds
2013-08-30 21:44                                   ` Al Viro
2013-08-30 22:30                                     ` Linus Torvalds
2013-08-31 21:23                                       ` Al Viro
2013-08-31 22:49                                         ` Linus Torvalds
2013-08-31 23:27                                           ` Al Viro
2013-09-01  0:13                                             ` Al Viro
2013-09-01 17:48                                               ` Al Viro
2013-09-09  8:30                                               ` Peter Zijlstra
2013-08-30 21:10                                 ` Waiman Long
2013-08-30 21:22                                   ` Linus Torvalds [this message]
2013-08-30 21:30                                   ` Al Viro
2013-08-30 21:42                                     ` Waiman Long
2013-08-30 19:40                         ` Al Viro
2013-08-30 19:52                           ` Waiman Long
2013-08-30 20:26                             ` Al Viro
2013-08-30 20:35                               ` Waiman Long
2013-08-30 20:48                                 ` Al Viro
2013-08-31  2:02                                   ` Waiman Long
2013-08-31  2:35                                     ` Al Viro
2013-08-31  2:42                                       ` Al Viro
2013-09-02 19:25                                         ` Waiman Long
2013-09-03  6:01                                           ` Ingo Molnar
2013-09-03  7:24                                             ` Sedat Dilek
2013-09-03 15:38                                               ` Linus Torvalds
2013-09-03 15:14                                             ` Waiman Long
2013-09-03 15:34                                               ` Linus Torvalds
2013-09-03 19:09                                                 ` Linus Torvalds
2013-09-03 21:01                                                   ` Waiman Long
2013-09-04 14:52                                                   ` Waiman Long
2013-09-04 15:14                                                     ` Linus Torvalds
2013-09-04 19:25                                                       ` Waiman Long
2013-09-04 21:34                                                         ` Linus Torvalds
2013-09-05  2:35                                                           ` Waiman Long
2013-09-05 13:31                                                     ` Ingo Molnar
2013-09-05 17:33                                                       ` Waiman Long
2013-09-05 17:40                                                         ` Ingo Molnar
2013-09-03 22:41                                               ` Sedat Dilek
2013-09-03 23:11                                                 ` Sedat Dilek
2013-09-08 21:45               ` Linus Torvalds
2013-09-09  0:03                 ` Al Viro
2013-09-09  0:25                   ` Linus Torvalds
2013-09-09  0:35                     ` Al Viro
2013-09-09  0:38                       ` Linus Torvalds
2013-09-09  0:57                         ` Al Viro
2013-09-09  2:09                     ` Ramkumar Ramachandra
2013-09-09  0:30                   ` Al Viro
2013-09-09  3:32                   ` Linus Torvalds
2013-09-09  4:06                     ` Ramkumar Ramachandra
2013-09-09  5:44                     ` Al Viro
2013-08-30 17:17           ` Peter Zijlstra
2013-08-30 17:28             ` Linus Torvalds
2013-08-30 17:33               ` Linus Torvalds
2013-08-29 15:20     ` Waiman Long
2013-08-06  3:12 ` [PATCH v7 2/4] spinlock: Enable x86 architecture to do lockless refcount update Waiman Long
2013-08-06  3:12 ` [PATCH v7 3/4] dcache: replace d_lock/d_count by d_lockcnt Waiman Long
2013-08-06  3:12 ` [PATCH v7 4/4] dcache: Enable lockless update of dentry's refcount Waiman Long
2013-08-13 18:03 ` [PATCH v7 0/4] Lockless update of reference count protected by spinlock Waiman Long
2013-08-31  3:06 [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount George Spelvin
2013-08-31 17:16 ` Linus Torvalds
2013-09-01  8:50   ` George Spelvin
2013-09-01 11:10     ` Theodore Ts'o
2013-09-01 15:49       ` Linus Torvalds
2013-09-01 18:11         ` Steven Rostedt
2013-09-01 20:03           ` Linus Torvalds

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