From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752317AbcEAR3A (ORCPT ); Sun, 1 May 2016 13:29:00 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:55285 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751610AbcEAR27 (ORCPT ); Sun, 1 May 2016 13:28:59 -0400 Date: Sun, 1 May 2016 10:28:54 -0700 From: Christoph Hellwig To: Waiman Long Cc: "Theodore Ts'o" , Andreas Dilger , Alexander Viro , Matthew Wilcox , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, Dave Chinner , Christoph Hellwig , Scott J Norton , Douglas Hatch , Toshimitsu Kani Subject: Re: [PATCH v5 0/2] ext4: Improve parallel I/O performance on NVDIMM Message-ID: <20160501172854.GA19601@infradead.org> References: <1461947276-25988-1-git-send-email-Waiman.Long@hpe.com> <57238DFC.6010108@hpe.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <57238DFC.6010108@hpe.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 29, 2016 at 12:38:20PM -0400, Waiman Long wrote: > From my testing, it looked like that parallel overwrites to the same file in > an ext4 filesystem on DAX can happen in parallel even if their range > overlaps. It was mainly because the code will drop the i_mutex before the > write. That means the overlapped blocks can get garbage. I think this is a > problem, but I am not expert in the ext4 filesystem to say for sure. I would > like to know your thought on that. That's another issue with dax I/O pretending to be direct I/O.. Because it isn't we'll need to synchronize it like buffered I/O and not like direct I/O in all file systems.