Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751356AbXAKSlg (ORCPT ); Thu, 11 Jan 2007 13:41:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751401AbXAKSlg (ORCPT ); Thu, 11 Jan 2007 13:41:36 -0500 Received: from pat.uio.no ([129.240.10.15]:58226 "EHLO pat.uio.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751356AbXAKSlf (ORCPT ); Thu, 11 Jan 2007 13:41:35 -0500 Subject: Re: O_DIRECT question From: Trond Myklebust To: Linus Torvalds Cc: Xavier Bestel , Nick Piggin , Aubrey , Hua Zhong , Hugh Dickins , linux-kernel@vger.kernel.org, hch@infradead.org, kenneth.w.chen@intel.com, akpm@osdl.org, mjt@tls.msk.ru In-Reply-To: References: <6d6a94c50701101857v2af1e097xde69e592135e54ae@mail.gmail.com> <45A5D4A7.7020202@yahoo.com.au> <1168534362.7365.3.camel@bip.parateam.prv> Content-Type: text/plain Date: Thu, 11 Jan 2007 13:41:15 -0500 Message-Id: <1168540875.6170.46.camel@lade.trondhjem.org> Mime-Version: 1.0 X-Mailer: Evolution 2.8.1 Content-Transfer-Encoding: 7bit X-UiO-Spam-info: not spam, SpamAssassin (score=-5.0, required=12.0, autolearn=disabled, UIO_MAIL_IS_INTERNAL=-5) X-UiO-Scanned: CC5960E53CC0D720CF450FC87794508036D0B213 X-UiO-SPAM-Test: 141.211.133.154 spam_score -49 maxlevel 200 minaction 2 bait 0 blacklist 0 greylist 0 ratelimit 0 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 896 Lines: 19 On Thu, 2007-01-11 at 09:04 -0800, Linus Torvalds wrote: > That is what I think some users could do. If the main issue with O_DIRECT > is the page cache allocations, if we instead had better (read: "any") > support for POSIX_FADV_NOREUSE, one class of reasons O_DIRECT usage would > just go away. For NFS, the main feature of interest when it comes to O_DIRECT is strictly uncached I/O. Replacing it with POSIX_FADV_NOREUSE won't help because it can't guarantee that the page will be thrown out of the page cache before some second process tries to read it. That is particularly true if some dopey third party process has mmapped the file. Trond - 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/