From: Andrew Morton Subject: Re: [PATCH] ext3,4:fdatasync should skip metadata writeout Date: Thu, 15 Nov 2007 18:59:19 -0800 Message-ID: <20071115185919.7df4cda9.akpm@linux-foundation.org> References: <6.0.0.20.2.20071116114652.03b9e4e8@172.19.0.2> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Hisashi Hifumi Return-path: In-Reply-To: <6.0.0.20.2.20071116114652.03b9e4e8@172.19.0.2> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Fri, 16 Nov 2007 11:47:27 +0900 Hisashi Hifumi wrote: > Currently fdatasync is identical to fsync in ext3,4. > I think fdatasync should skip journal flush in data=ordered and data=writeback mode > because this syscall is not required to synchronize the metadata. I suppose so. Although one wonders what earthly point there is in syncing a file's data if we haven't yet written out the metadata which is required for locating that data. IOW, fdatasync() is only useful if the application knows that it is overwriting already-instantiated blocks. In which case it might as well have used fsync(). For ext2-style filesystems, anyway. hm. It needs some thought.