From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Lokier Subject: Re: [PATCH 4/4] ext4: call blkdev_issue_flush on fsync Date: Tue, 20 May 2008 16:43:14 +0100 Message-ID: <20080520154313.GI16676@shareable.org> References: <482DDA56.6000301@redhat.com> <482DDC04.7020706@redhat.com> <20080520023454.GM15035@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Theodore Tso , Eric Sandeen , ext4 development , linux-kernel Mailing List , linux-fsdevel Return-path: Received: from mail2.shareable.org ([80.68.89.115]:52857 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934338AbYETPnb (ORCPT ); Tue, 20 May 2008 11:43:31 -0400 Content-Disposition: inline In-Reply-To: <20080520023454.GM15035@mit.edu> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Theodore Tso wrote: > On Fri, May 16, 2008 at 02:09:56PM -0500, Eric Sandeen wrote: > > To ensure that bits are truly on-disk after an fsync, > > we should call blkdev_issue_flush if barriers are supported. > > This patch isn't necessary, and in fact will cause a double flush. > When you call fsync(), it calls ext4_force_commit(), and we do a the > equivalent of a blkdev_issue_flush() today (which is what happenes > when you do a submit_bh(WRITE_BARRIER, bh), which is what setting > set_ordered_mode(bh) ends up causing. ISTR fsync() on ext3 did not always force a commit, if in-place data writes did not change any metadata. Has this been fixed in ext4 but not ext3 then? Does WRITE_BARRIER always cause a flush? It does not have to according to Documentation/block/barrier.txt. There are caveats about tagged queuing "not yet implemented" in the text, but can we rely on that? The documentation is older than the current implementation; those caveats might no longer apply. -- Jamie