From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 6113F6B0082 for ; Wed, 3 Jun 2009 10:56:06 -0400 (EDT) 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: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org 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" 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org