Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750729AbXAKPvG (ORCPT ); Thu, 11 Jan 2007 10:51:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750738AbXAKPvG (ORCPT ); Thu, 11 Jan 2007 10:51:06 -0500 Received: from smtp.osdl.org ([65.172.181.24]:41753 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750729AbXAKPvF (ORCPT ); Thu, 11 Jan 2007 10:51:05 -0500 Date: Thu, 11 Jan 2007 07:50:26 -0800 (PST) From: Linus Torvalds To: Nick Piggin cc: 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 Subject: Re: O_DIRECT question In-Reply-To: <45A5D4A7.7020202@yahoo.com.au> Message-ID: References: <6d6a94c50701101857v2af1e097xde69e592135e54ae@mail.gmail.com> <45A5D4A7.7020202@yahoo.com.au> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1381 Lines: 32 On Thu, 11 Jan 2007, Nick Piggin wrote: > > Speaking of which, why did we obsolete raw devices? And/or why not just > go with a minimal O_DIRECT on block device support? Not a rhetorical > question -- I wasn't involved in the discussions when they happened, so > I would be interested. Lots of people want to put their databases in a file. Partitions really weren't nearly flexible enough. So the whole raw device or O_DIRECT just to the block device thing isn't really helping any. > 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. Except by teaching people not to use it, and making the normal paths fast enough (and that _includes_ doing things like dropping caches more aggressively, but it probably would include more work on the device queue merging stuff etc etc). The "good" news is that CPU really is outperforming disk more and more, so the extra cost of managing the page cache keeps on getting smaller and smaller, and (fingers crossed) some day we can hopefully just drop O_DIRECT and nobody will care. 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/