From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755168AbZBCW3x (ORCPT ); Tue, 3 Feb 2009 17:29:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751983AbZBCW3o (ORCPT ); Tue, 3 Feb 2009 17:29:44 -0500 Received: from waste.org ([66.93.16.53]:43689 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751134AbZBCW3n (ORCPT ); Tue, 3 Feb 2009 17:29:43 -0500 Subject: Re: [PATCH 2/4] Convert epoll to a bitlock From: Matt Mackall To: Andrew Morton Cc: Eric Dumazet , 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, alan@lxorguk.ukuu.org.uk In-Reply-To: <20090203140543.6e915f97.akpm@linux-foundation.org> References: <1233598811-6871-1-git-send-email-corbet@lwn.net> <1233598811-6871-3-git-send-email-corbet@lwn.net> <20090203133942.2ecec281.akpm@linux-foundation.org> <4988BD4E.8080206@cosmosbay.com> <20090203140543.6e915f97.akpm@linux-foundation.org> Content-Type: text/plain Date: Tue, 03 Feb 2009 16:22:02 -0600 Message-Id: <1233699722.3243.127.camel@calx> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2009-02-03 at 14:05 -0800, Andrew Morton wrote: > On Tue, 03 Feb 2009 22:55:26 +0100 > Eric Dumazet wrote: > > > Andrew Morton a __crit : > > > On Mon, 2 Feb 2009 11:20:09 -0700 > > > Jonathan Corbet 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. And lockdep doesn't know about > > > it. > > > > > > > In a previous attempt (2005), I suggested using a single global lock. > > > > http://search.luky.org/linux-kernel.2005/msg50862.html > > ok.. > > > Probably an array of hashed spinlocks would be more than enough. > > > > yes, f_ep_lock is a teeny innermost lock. Perhaps using > f->f_dentry->d_inode->i_lock would be a decent speed/space compromise. That seems eminently reasonable. But that re-opens the question of what to do about poor Jon's quest. I got confused halfway through as he went from using a global fasync spinlock to a non-locked but atomic flag bit. Not sure why using a per-file or per-inode lock doesn't work for the fasync code. -- http://selenic.com : development and support for Mercurial and Linux