Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752890AbYKYQRT (ORCPT ); Tue, 25 Nov 2008 11:17:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752078AbYKYQRI (ORCPT ); Tue, 25 Nov 2008 11:17:08 -0500 Received: from mout-xforward.kundenserver.de ([212.227.17.5]:55688 "EHLO mout-xforward.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751676AbYKYQRH (ORCPT ); Tue, 25 Nov 2008 11:17:07 -0500 Message-ID: <492C2502.7070709@vlnb.net> Date: Tue, 25 Nov 2008 19:17:06 +0300 From: Vladislav Bolkhovitin User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: Jeff Moyer CC: Vladislav Bolkhovitin , Wu Fengguang , Jens Axboe , "Vitaly V. Bursov" , linux-kernel@vger.kernel.org Subject: Re: Slow file transfer speeds with CFQ IO scheduler in some cases References: <4917263D.2090904@telenet.dn.ua> <20081110104423.GA26778@kernel.dk> <20081110135618.GI26778@kernel.dk> <20081112190227.GS26778@kernel.dk> <1226566313.199910.29888@de> <20081113085439.GZ26778@kernel.dk> <1226626590.681364.9398@de> <492BDB55.3050407@vlnb.net> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Provags-ID: V01U2FsdGVkX1/GBMlKzXdsiV3UEC4MVhEuj+M50PGQC5O7YzU 87nHJx398TXjCnoagbuRNS/EElXwqwr43bZw0pwdJzgjcncjhU FSBV9EU55tsPowkFgqJNg== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1539 Lines: 36 Jeff Moyer wrote: > Vladislav Bolkhovitin writes: > >> Wu Fengguang wrote: >>> Another scheme is to detect the sequential pattern via looking up >>> the page cache, which provides one single and consistent view of the >>> pages recently accessed. That makes sequential detection possible. >>> >>> The cost will be one extra page cache lookup per random read. >>> If it's not acceptable, the corresponding code could be disabled >>> by default. >> I think, this should be the best and the simplest way to go. Since in >> most case data from the cache should be later copied to user, one more >> page cache lookup should be negligible. > > I haven't thought about your suggestion in any detail, but it seems to > me that you will not handle O_DIRECT I/O with this scheme. And shouldn't. One using O_DIRECT is supposed to understand and accept that no features provided by page cache, including read ahead, will be available to him. Hence, if necessary, he must implement own read ahead procedures. > Cheers, > Jeff > -- > 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/ > -- 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/