From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 66D306B0253 for ; Mon, 2 May 2016 11:51:35 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id 203so359293614pfy.2 for ; Mon, 02 May 2016 08:51:35 -0700 (PDT) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.136]) by mx.google.com with ESMTPS id o86si2010256pfi.217.2016.05.02.08.51.34 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 May 2016 08:51:34 -0700 (PDT) Message-ID: <1462204291.11211.20.camel@kernel.org> Subject: Re: [PATCH v4 5/7] fs: prioritize and separate direct_io from dax_io From: Vishal Verma Date: Mon, 02 May 2016 09:51:31 -0600 In-Reply-To: <5727753F.6090104@plexistor.com> References: <1461878218-3844-1-git-send-email-vishal.l.verma@intel.com> <1461878218-3844-6-git-send-email-vishal.l.verma@intel.com> <5727753F.6090104@plexistor.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Boaz Harrosh , Vishal Verma , linux-nvdimm@lists.01.org Cc: linux-block@vger.kernel.org, Jan Kara , Matthew Wilcox , Dave Chinner , linux-kernel@vger.kernel.org, xfs@oss.sgi.com, Jens Axboe , linux-mm@kvack.org, Al Viro , Christoph Hellwig , linux-fsdevel@vger.kernel.org, Andrew Morton , linux-ext4@vger.kernel.org On Mon, 2016-05-02 at 18:41 +0300, Boaz Harrosh wrote: > On 04/29/2016 12:16 AM, Vishal Verma wrote: > > > > All IO in a dax filesystem used to go through dax_do_io, which > > cannot > > handle media errors, and thus cannot provide a recovery path that > > can > > send a write through the driver to clear errors. > > > > Add a new iocb flag for DAX, and set it only for DAX mounts. In the > > IO > > path for DAX filesystems, use the same direct_IO path for both DAX > > and > > direct_io iocbs, but use the flags to identify when we are in > > O_DIRECT > > mode vs non O_DIRECT with DAX, and for O_DIRECT, use the > > conventional > > direct_IO path instead of DAX. > > > Really? What are your thinking here? > > What about all the current users of O_DIRECT, you have just made them > 4 times slower and "less concurrent*" then "buffred io" users. Since > direct_IO path will queue an IO request and all. > (And if it is not so slow then why do we need dax_do_io at all? > [Rhetorical]) > > I hate it that you overload the semantics of a known and expected > O_DIRECT flag, for special pmem quirks. This is an incompatible > and unrelated overload of the semantics of O_DIRECT. We overloaded O_DIRECT a long time ago when we made DAX piggyback on the same path: static inline bool io_is_direct(struct file *filp) { return (filp->f_flags & O_DIRECT) || IS_DAX(filp->f_mapping->host); } Yes O_DIRECT on a DAX mounted file system will now be slower, but - > > > > > This allows us a recovery path in the form of opening the file with > > O_DIRECT and writing to it with the usual O_DIRECT semantics > > (sector > > alignment restrictions). > > > I understand that you want a sector aligned IO, right? for the > clear of errors. But I hate it that you forced all O_DIRECT IO > to be slow for this. > Can you not make dax_do_io handle media errors? At least for the > parts of the IO that are aligned. > (And your recovery path application above can use only aligned > A IO to make sure) > > Please look for another solution. Even a special > IOCTL_DAX_CLEAR_ERROR A - see all the versions of this series prior to this one, where we try to do a fallback... > > [*"less concurrent" because of the queuing done in bdev. Note how > A pmem is not even multi-queue, and even if it was it will be much > A slower then DAX because of the code depth and all the locks and > task > A switches done in the block layer. In DAX the final memcpy is done > directly > A on the user-mode thread] > > Thanks > Boaz > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org