From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>,
linux-kernel@vger.kernel.org, andi@firstfloor.org,
oleg@redhat.com, viro@zeniv.linux.org.uk,
davidel@xmailserver.org, davem@davemloft.net, hch@lst.de,
linux-api@vger.kernel.org, mpm@selenic.com,
alan@lxorguk.ukuu.org.uk
Subject: Re: [PATCH 2/4] Convert epoll to a bitlock
Date: Wed, 4 Feb 2009 15:54:27 +1100 [thread overview]
Message-ID: <200902041554.29184.nickpiggin@yahoo.com.au> (raw)
In-Reply-To: <20090203133942.2ecec281.akpm@linux-foundation.org>
On Wednesday 04 February 2009 08:39:42 Andrew Morton wrote:
> On Mon, 2 Feb 2009 11:20:09 -0700
>
> Jonathan Corbet <corbet@lwn.net> wrote:
> > Matt Mackall suggested converting epoll's ep_lock to a bitlock as a way
> > of saving space in struct file. This patch makes that change.
>
> hrm. bit_spin_lock() makes people upset (large penguiny people). iirc
> it doesn't have all the correct/well-understood memory/compiler
> ordering semantics which spinlocks have.
Bit spinlocks are OK now they are using lock bitops. Of course, they are
even nicer (and become very comparable to spinlocks) if you can use the
non-atomic unlock __bit_spin_unlock().
But it seems probably like another approach being discussed is a better
idea anyway.
> And lockdep doesn't know about
> it.
This is a valid concern. Someone had a patch to add lockdep support to it,
which might be a good idea to do. But for small inner locks, maybe not a
huge problem.
next prev parent reply other threads:[~2009-02-04 4:55 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-02 18:20 [PATCH/RFC] F_SETFL/Fasync BKL removal, now without unsightly global locks Jonathan Corbet
2009-02-02 18:20 ` [PATCH 1/4] Use bit operations for file->f_flags Jonathan Corbet
2009-02-03 21:37 ` Andrew Morton
2009-02-02 18:20 ` [PATCH 2/4] Convert epoll to a bitlock Jonathan Corbet
2009-02-03 21:39 ` Andrew Morton
2009-02-03 21:55 ` Eric Dumazet
2009-02-03 22:05 ` Andrew Morton
2009-02-03 22:22 ` Matt Mackall
2009-02-03 22:37 ` Jonathan Corbet
2009-02-03 22:53 ` Andrew Morton
2009-02-03 23:09 ` Davide Libenzi
2009-02-03 23:12 ` Davide Libenzi
2009-02-03 23:19 ` Jonathan Corbet
2009-02-03 23:29 ` Andrew Morton
2009-02-04 7:13 ` Christoph Hellwig
2009-02-04 7:20 ` Nick Piggin
2009-02-04 13:34 ` Jonathan Corbet
2009-02-04 16:51 ` Davide Libenzi
2009-02-03 23:08 ` Davide Libenzi
2009-02-04 2:48 ` Eric Dumazet
2009-02-04 1:00 ` wli
2009-02-04 4:54 ` Nick Piggin [this message]
2009-02-02 18:20 ` [PATCH 3/4] Move FASYNC bit handling to f_op->fasync() Jonathan Corbet
2009-02-02 18:20 ` [PATCH 4/4] Rationalize fasync return values Jonathan Corbet
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