Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932247AbXALRD3 (ORCPT ); Fri, 12 Jan 2007 12:03:29 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932292AbXALRD3 (ORCPT ); Fri, 12 Jan 2007 12:03:29 -0500 Received: from mx33.mail.ru ([194.67.23.194]:1067 "EHLO mx33.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932247AbXALRD2 (ORCPT ); Fri, 12 Jan 2007 12:03:28 -0500 Message-ID: <45A7BF53.2090006@inbox.ru> Date: Fri, 12 Jan 2007 20:03:15 +0300 From: Viktor User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20060212 Fedora/1.7.12-5 X-Accept-Language: en-us, ru, en MIME-Version: 1.0 To: Linus Torvalds CC: Nick Piggin , Aubrey , Hua Zhong , Hugh Dickins , linux-kernel@vger.kernel.org, hch@infradead.org, kenneth.w.chen@intel.com, akpm@osdl.org Subject: Re: O_DIRECT question References: <6d6a94c50701101857v2af1e097xde69e592135e54ae@mail.gmail.com> <45A5D4A7.7020202@yahoo.com.au> <1168534362.7365.3.camel@bip.parateam.prv> In-Reply-To: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1570 Lines: 37 Linus Torvalds wrote: >>>>O_DIRECT is still crazily racy versus pagecache operations. >>> >>>Yes. O_DIRECT is really fundamentally broken. There's just no way to fix >>>it sanely. >> >>How about aliasing O_DIRECT to POSIX_FADV_NOREUSE (sortof) ? > > > 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. > > See also the patch that Roy Huang posted about another approach to the > same problem: just limiting page cache usage explicitly. > > That's not the _only_ issue with O_DIRECT, though. It's one big one, but > people like to think that the memory copy makes a difference when you do > IO too (I think it's likely pretty debatable in real life, but I'm totally > certain you can benchmark it, probably even pretty easily especially if > you have fairly studly IO capabilities and a CPU that isn't quite as > studly). > > So POSIX_FADV_NOREUSE kind of support is one _part_ of the O_DIRECT > picture, and depending on your problems (in this case, the embedded world) > it may even be the *biggest* part. But it's not the whole picture. >From 2.6.19 sources it looks like POSIX_FADV_NOREUSE is no-op there > Linus - 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/