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From: Linus Torvalds <torvalds@linux-foundation.org>
To: David Howells <dhowells@redhat.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Nicolas Dichtel <nicolas.dichtel@6wind.com>,
	raven@themaw.net, Christian Brauner <christian@brauner.io>,
	keyrings@vger.kernel.org, linux-usb@vger.kernel.org,
	linux-block <linux-block@vger.kernel.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length [ver #2]
Date: Sun, 27 Oct 2019 10:03:35 -0400	[thread overview]
Message-ID: <CAHk-=wh7cf3ANq-G9MmwSQiUK2d-=083C0HV_8hTGe2Mb4X7JA@mail.gmail.com> (raw)
In-Reply-To: <157186186167.3995.7568100174393739543.stgit@warthog.procyon.org.uk>

This still has signs of that earlier series:

On Wed, Oct 23, 2019 at 4:17 PM David Howells <dhowells@redhat.com> wrote:
>
>                 if (rem >= ibuf->len) {
>                         *obuf = *ibuf;
>                         ibuf->ops = NULL;
> -                       pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
> -                       pipe->nrbufs--;
> +                       tail++;
> +                       pipe_commit_read(pipe, tail);
>                 } else {
>                         if (!pipe_buf_get(pipe, ibuf))
>                                 goto out_free;

with those odd "pipe_commit_read/write()" helpers.

They make no sense, and they don't make things more legible.

It's shorter and more obvious to just write

   pipe->head = head;

than it is to write

   pipe_commit_write(pipe, head);

Even when the addition of the notifications,  it's all under the
pipe->wait.lock, so it's all just regular assignments.

Now, if at some point it starts doing fancy lockless things, at _that_
point the updates might become more complex, but that's a potential
future thing that wouldn't be relevant for a while, and isn't a reason
to make the code more obscure now.

Hmm?

             Linus

  parent reply	other threads:[~2019-10-27 14:03 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-23 20:17 [RFC PATCH 00/10] pipe: Notification queue preparation [ver #2] David Howells
2019-10-23 20:17 ` [RFC PATCH 01/10] pipe: Reduce #inclusion of pipe_fs_i.h " David Howells
2019-10-23 20:17 ` [RFC PATCH 02/10] Remove the nr_exclusive argument from __wake_up_sync_key() " David Howells
2019-10-23 20:17 ` [RFC PATCH 03/10] Add wake_up_interruptible_sync_poll_locked() " David Howells
2019-10-23 20:17 ` [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length " David Howells
2019-10-26 14:58   ` [pipe] 6567a02d20: BUG:kernel_NULL_pointer_dereference,address kernel test robot
2019-10-27 14:03   ` Linus Torvalds [this message]
2019-10-30 16:19   ` [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length [ver #2] Ilya Dryomov
2019-10-30 20:35     ` Rasmus Villemoes
2019-10-30 22:16       ` Ilya Dryomov
2019-10-30 22:38         ` Rasmus Villemoes
2019-10-31 15:11     ` David Howells
2019-10-31 15:57       ` Ilya Dryomov
2019-11-01 14:53       ` David Howells
2019-10-31 14:57   ` David Howells
2019-11-03 11:17     ` Matthew Wilcox
2019-12-06 21:47   ` Johannes Hirte
2019-12-06 22:14     ` Linus Torvalds
2019-12-07  0:00       ` Johannes Hirte
2019-12-07  1:03         ` Linus Torvalds
2019-12-08 17:56           ` Johannes Hirte
2019-12-08 18:10             ` Linus Torvalds
2019-12-07  6:47         ` Linus Torvalds
2019-12-06 22:15   ` David Howells
2019-10-23 20:17 ` [RFC PATCH 05/10] pipe: Allow pipes to have kernel-reserved slots " David Howells
2019-10-23 20:18 ` [RFC PATCH 06/10] pipe: Advance tail pointer inside of wait spinlock in pipe_read() " David Howells
2019-10-23 20:18 ` [RFC PATCH 07/10] pipe: Conditionalise wakeup " David Howells
2019-10-27 15:57   ` Konstantin Khlebnikov
2019-10-31 15:21   ` David Howells
2019-10-31 16:38   ` David Howells
2019-11-03 11:04     ` Konstantin Khlebnikov
2019-10-23 20:18 ` [RFC PATCH 08/10] pipe: Rearrange sequence in pipe_write() to preallocate slot " David Howells
2019-10-23 20:18 ` [RFC PATCH 09/10] pipe: Remove redundant wakeup from pipe_write() " David Howells
2019-10-23 20:18 ` [RFC PATCH 10/10] pipe: Check for ring full inside of the spinlock in " David Howells
2019-10-24 10:32 ` [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length " David Howells
2019-10-24 13:14 ` [RFC PATCH 00/10] pipe: Notification queue preparation " Peter Zijlstra
2019-10-24 16:57 ` [RFC PATCH 11/10] pipe: Add fsync() support " David Howells
2019-10-24 21:29   ` Linus Torvalds
2019-10-25  8:34   ` David Howells
2019-10-27 15:22   ` Christoph Hellwig
2019-10-27 16:04   ` Konstantin Khlebnikov
2019-10-31 15:13   ` David Howells
2019-10-31 15:15   ` David Howells
2019-11-02 18:53     ` Linus Torvalds
2019-11-02 19:34     ` David Howells
2019-11-02 20:31       ` Andy Lutomirski
2019-11-02 22:03         ` Linus Torvalds
2019-11-02 22:09           ` Linus Torvalds
2019-11-02 22:30           ` Andy Lutomirski
2019-11-02 23:02             ` Linus Torvalds
2019-11-02 23:09               ` Linus Torvalds
2019-11-02 23:14                 ` Andy Lutomirski
2019-11-03 12:02                   ` Konstantin Khlebnikov

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