From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 04/23] vfs: Introduce infrastructure for revoking a file Date: Tue, 02 Jun 2009 15:56:02 -0700 Message-ID: References: <1243893048-17031-4-git-send-email-ebiederm@xmission.com> <20090602071411.GE31556@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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" To: Nick Piggin Return-path: 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 In-Reply-To: <20090602071411.GE31556@wotan.suse.de> (Nick Piggin's message of "Tue\, 2 Jun 2009 09\:14\:11 +0200") Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 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