From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757673AbZJLSit (ORCPT ); Mon, 12 Oct 2009 14:38:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757658AbZJLSis (ORCPT ); Mon, 12 Oct 2009 14:38:48 -0400 Received: from srv5.dvmed.net ([207.36.208.214]:37788 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757646AbZJLSis (ORCPT ); Mon, 12 Oct 2009 14:38:48 -0400 Message-ID: <4AD37790.8090404@garzik.org> Date: Mon, 12 Oct 2009 14:38:08 -0400 From: Jeff Garzik User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.4pre) Gecko/20090922 Fedora/3.0-2.7.b4.fc11 Thunderbird/3.0b4 MIME-Version: 1.0 To: Jeff Moyer CC: Linux Kernel Mailing , Jens Axboe Subject: Re: blkdev_issue_flush really issues a WRITE_BARRIER -- is that okay? References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -4.4 (----) X-Spam-Report: SpamAssassin version 3.2.5 on srv5.dvmed.net summary: Content analysis details: (-4.4 points, 5.0 required) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/12/2009 01:31 PM, Jeff Moyer wrote: > Hi, > > While looking though Christoph's patch to call blkdev_issue_flush for > fsync on block devices, I noticed that it only issues a WRITE_BARRIER. > I don't see how that guarantees that data is on stable storage. Am I > missing something? Shouldn't this translate to a FLUSH CACHE or > SYNCHRONIZE CACHE command? Barriers are a high level primitive that exist at the block layer level. Lower level storage drivers then convert barriers to a hardware-specific low level primitive such as SYNCHRONIZE CACHE or FUA. Jeff