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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham 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 AB038C48BD6 for ; Tue, 25 Jun 2019 19:14:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B7792086D for ; Tue, 25 Jun 2019 19:14:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732993AbfFYTOp (ORCPT ); Tue, 25 Jun 2019 15:14:45 -0400 Received: from mx2.suse.de ([195.135.220.15]:52714 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730939AbfFYTOp (ORCPT ); Tue, 25 Jun 2019 15:14:45 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 1F3A1ABD7; Tue, 25 Jun 2019 19:14:44 +0000 (UTC) Date: Tue, 25 Jun 2019 14:14:42 -0500 From: Goldwyn Rodrigues To: Christoph Hellwig Cc: linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, darrick.wong@oracle.com, david@fromorbit.com Subject: Re: [PATCH 1/6] iomap: Use a IOMAP_COW/srcmap for a read-modify-write I/O Message-ID: <20190625191442.m27cwx5o6jtu2qch@fiona> References: <20190621192828.28900-1-rgoldwyn@suse.de> <20190621192828.28900-2-rgoldwyn@suse.de> <20190624070734.GB3675@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190624070734.GB3675@lst.de> User-Agent: NeoMutt/20180716 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 9:07 24/06, Christoph Hellwig wrote: > xfs will need to be updated to fill in the additional iomap for the > COW case. Has this series been tested on xfs? > No, I have not tested this, or make xfs set IOMAP_COW. I will try to do it in the next iteration. > I can't say I'm a huge fan of this two iomaps in one method call > approach. I always though two separate iomap iterations would be nicer, > but compared to that even the older hack with just the additional > src_addr seems a little better. I am just expanding on your idea of using multiple iterations for the Cow case in the hope we can come out of a good design: 1. iomap_file_buffered_write calls iomap_apply with IOMAP_WRITE flag. which calls iomap_begin() for the respective filesystem. 2. btrfs_iomap_begin() sets up iomap->type as IOMAP_COW and fills iomap struct with read addr information. 3. iomap_apply() conditionally for IOMAP_COW calls do_cow(new function) and calls ops->iomap_begin() with flag IOMAP_COW_READ_DONE(new flag). 4. btrfs_iomap_begin() fills up iomap structure with write information. Step 3 seems out of place because iomap_apply should be iomap.type agnostic. Right? Should we be adding another flag IOMAP_COW_DONE, just to figure out that this is the "real" write for iomap_begin to fill iomap? If this is not how you imagined, could you elaborate on the dual iteration sequence? -- Goldwyn