From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5E321C282DA for ; Tue, 16 Apr 2019 16:52:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2959E206B6 for ; Tue, 16 Apr 2019 16:52:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="FSFiREk3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729712AbfDPQwY (ORCPT ); Tue, 16 Apr 2019 12:52:24 -0400 Received: from mail-oi1-f193.google.com ([209.85.167.193]:43710 "EHLO mail-oi1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727180AbfDPQwY (ORCPT ); Tue, 16 Apr 2019 12:52:24 -0400 Received: by mail-oi1-f193.google.com with SMTP id t81so17552107oig.10 for ; Tue, 16 Apr 2019 09:52:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=yzroFUTL3qdzXgy0/HOd8rRb5RiTiJrQnHckuVTi0m0=; b=FSFiREk3fEXjg/mbFruT9cjPWa80srAsXgLnGsgpKGNYxvPhBQ3HMDNCBrQpUPZVxp cHYRXf+M6HVpUR4/HYsVNjvCFfLxt/QLcAbKywd0OIGdf7KdwV50gyi4DfzeLoHux5A/ NFm9Eo/vYIZr8C9/OhsaUNrvkuepVMPhIyGwxXC4aJL1Cnz8601y1nHTKcFzRYZLDP88 FD3Uv2y916L8varemjeq2DmuJrxYG/E/ZXulXcPLdZMOtpyiUTII3kfGIiW62Dk3when cWkZj3he9bDASj6cat2fQQ8E3OVUUoqDcy/CQbgXSiJSk+x6YWqh866Az8CydE1Ocg9T cG5A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=yzroFUTL3qdzXgy0/HOd8rRb5RiTiJrQnHckuVTi0m0=; b=tsw9u7qIstTyUbzorUge36M1pdJV5ttOTaPtw00veflNT69UpIC45ZqBB5Hgou5H5j WiTXDQHa7a7ix6GPeR4mmYZsne38G8SnvfavvnmWREeTMR8j2TADIOP8WR+aygoRWsYQ a3zqdXOsndvnbPr28C3x7Z02LtCJkygjCTeVuPoM3MJOm8zEFo3MjAGDCn2MBpphQWdw Gd7o9md+MkqfsVfzElSchAv5y4oibZRI5rYZZ1o5DHkFCLxVl5sUYYJDyOFJfoWyhRzi XrRbaD+IpqcND/uo0qR6WlY7mAY1NiRm5h2fOnFxFPdDAhZ6SQqn2JlxhoWN2owcZGOd 8Z7A== X-Gm-Message-State: APjAAAXZ5wBUIOeQkT8wHyVtPILUmCArk8gqdqvccguqk+AkjTsw6gqY UJkqiFzWtBFk2N4RYOXNRtQ20eJY8X22oIhadt5Nbw== X-Google-Smtp-Source: APXvYqxurP6qNuhwJ0pfL1LFK5ePAHfLMiff5uZA1sV7wNqgUoTLMMK6rqw5NV004jzzqUqjg4A4kLJ6yvQ+do+RskY= X-Received: by 2002:aca:e64f:: with SMTP id d76mr25850764oih.105.1555433543227; Tue, 16 Apr 2019 09:52:23 -0700 (PDT) MIME-Version: 1.0 References: <20190416164154.30390-1-rgoldwyn@suse.de> <20190416164154.30390-2-rgoldwyn@suse.de> In-Reply-To: <20190416164154.30390-2-rgoldwyn@suse.de> From: Dan Williams Date: Tue, 16 Apr 2019 09:52:12 -0700 Message-ID: Subject: Re: [PATCH 01/18] btrfs: create a mount option for dax To: Goldwyn Rodrigues Cc: linux-btrfs@vger.kernel.org, kilobyte@angband.pl, Jan Kara , "Darrick J. Wong" , nborisov@suse.com, linux-nvdimm , david , dsterba@suse.cz, Matthew Wilcox , linux-fsdevel , Christoph Hellwig , Goldwyn Rodrigues Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Apr 16, 2019 at 9:42 AM Goldwyn Rodrigues wrote: > > From: Goldwyn Rodrigues > > This sets S_DAX in inode->i_flags, which can be used with > IS_DAX(). > > The dax option is restricted to non multi-device mounts. > dax interacts with the device directly instead of using bio, so > all bio-hooks which we use for multi-device cannot be performed > here. While regular read/writes could be manipulated with > RAID0/1, mmap() is still an issue. > > Auto-setting free space tree, because dealing with free space > inode (specifically readpages) is a nightmare. > Auto-setting nodatasum because we don't get callback for writing > checksums after mmap()s. > Deny compression because it does not work with direct I/O. I'd like to consider the dax mount option deprecated and require new implementations to use a dynamic scheme that Darrick and I once discussed where "dax" (or more specifically the MAP_SYNC semantic) is an attribute that can be set on an empty directory and then inherited by all files / directories created in that hierarchy. Dax mappings are not always a performance win and enabling it for all files in the filesystem is potentially overkill, and I'm of opinion that we should step away from an filesystem-global mount option.