Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755645AbZFBW4T (ORCPT ); Tue, 2 Jun 2009 18:56:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753425AbZFBW4F (ORCPT ); Tue, 2 Jun 2009 18:56:05 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:40464 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753420AbZFBW4D (ORCPT ); Tue, 2 Jun 2009 18:56:03 -0400 To: Nick Piggin Cc: Al Viro , 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 , Andrew Morton , Christoph Hellwig , "Eric W. Biederman" Subject: Re: [PATCH 04/23] vfs: Introduce infrastructure for revoking a file References: <1243893048-17031-4-git-send-email-ebiederm@xmission.com> <20090602071411.GE31556@wotan.suse.de> From: ebiederm@xmission.com (Eric W. Biederman) Date: Tue, 02 Jun 2009 15:56:02 -0700 In-Reply-To: <20090602071411.GE31556@wotan.suse.de> (Nick Piggin's message of "Tue\, 2 Jun 2009 09\:14\:11 +0200") 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=76.21.114.89;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 76.21.114.89 X-SA-Exim-Rcpt-To: npiggin@suse.de, ebiederm@aristanetworks.com, hch@infradead.org, akpm@linux-foundation.org, 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, viro@ZenIV.linux.org.uk X-SA-Exim-Mail-From: ebiederm@xmission.com X-SA-Exim-Scanned: No (on in01.mta.xmission.com); Exit with error (see exim mainlog) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1090 Lines: 27 Nick Piggin writes: >> In addition for a complete solution we need: >> - A reliable way the file structures that we need to revoke. >> - To wait for but not tamper with ongoing file creation and cleanup. >> - A guarantee that all with user space controlled duration are removed. >> >> The file_hotplug_lock has a very unique implementation necessitated by >> the need to have no performance impact on existing code. Classic locking > > Well, it isn't no performance impact. Function calls, branches, icache > and dcache... Practically none. Everything I could measure was in the noise. It is cheaper than any serializing locking primitive. I ran both lmbench and did some microbenchmark testing. So I know on the fast path the overhead is minimal. Certainly less than what we are doing in sysfs and proc today. 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/