Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753357AbZDLUV4 (ORCPT ); Sun, 12 Apr 2009 16:21:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752809AbZDLUVn (ORCPT ); Sun, 12 Apr 2009 16:21:43 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:38382 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752222AbZDLUVm (ORCPT ); Sun, 12 Apr 2009 16:21:42 -0400 To: Al Viro Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Hugh Dickins , Tejun Heo , Alexey Dobriyan , Linus Torvalds , Alan Cox , Greg Kroah-Hartman References: <20090411155852.GV26366@ZenIV.linux.org.uk> <20090411165651.GW26366@ZenIV.linux.org.uk> From: ebiederm@xmission.com (Eric W. Biederman) Date: Sun, 12 Apr 2009 13:21:35 -0700 In-Reply-To: <20090411165651.GW26366@ZenIV.linux.org.uk> (Al Viro's message of "Sat\, 11 Apr 2009 17\:56\:51 +0100") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=in01.mta.xmission.com;;;ip=67.169.126.145;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 67.169.126.145 X-SA-Exim-Rcpt-To: viro@ZenIV.linux.org.uk, gregkh@suse.de, alan@lxorguk.ukuu.org.uk, torvalds@linux-foundation.org, adobriyan@gmail.com, tj@kernel.org, hugh@veritas.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa03 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Al Viro X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -2.6 BAYES_00 BODY: Bayesian spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa03 1397; Body=1 Fuz1=1 Fuz2=1] * 1.6 XMSubMetaSx_00 1+ Sexy Words * 0.0 XM_SPF_Neutral SPF-Neutral * 0.4 UNTRUSTED_Relay Comes from a non-trusted relay Subject: Re: [RFC][PATCH 0/9] File descriptor hot-unplug support X-SA-Exim-Version: 4.2.1 (built Thu, 25 Oct 2007 00:26:12 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1130 Lines: 27 Al Viro writes: > On Sat, Apr 11, 2009 at 09:49:36AM -0700, Eric W. Biederman wrote: > >> The fact that in the common case only one task ever accesses a struct >> file leaves a lot of room for optimization. > > I'm not at all sure that it's a good assumption; even leaving aside e.g. > several tasks sharing stdout/stderr, a bunch of datagrams coming out of > several threads over the same socket is quite possible. I have thought about this a little more and a solution to ensure this is not a problem for code that has not opted in to this new functionality is simple. Require uses that need it to set FMODE_REVOKE. It is no extra code and it keeps the absolute worst case behavior for existing code down an additional branch mispredict. It is worth doing anyway because it cleans up the abstraction and makes it clear where revoke is supported. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/