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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_NEOMUTT 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 C22C4C4360F for ; Wed, 27 Mar 2019 18:59:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9EC4B205F4 for ; Wed, 27 Mar 2019 18:59:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389904AbfC0S66 (ORCPT ); Wed, 27 Mar 2019 14:58:58 -0400 Received: from mx2.suse.de ([195.135.220.15]:48526 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2389406AbfC0S66 (ORCPT ); Wed, 27 Mar 2019 14:58:58 -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 D1F65B027; Wed, 27 Mar 2019 18:58:55 +0000 (UTC) Date: Wed, 27 Mar 2019 13:58:53 -0500 From: Goldwyn Rodrigues To: "Darrick J. Wong" Cc: linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 04/15] dax: Introduce IOMAP_F_COW for copy-on-write Message-ID: <20190327185853.cxb6oou3bwla3jsy@merlin> References: <20190326190301.32365-1-rgoldwyn@suse.de> <20190326190301.32365-5-rgoldwyn@suse.de> <20190327175414.GB1172@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190327175414.GB1172@magnolia> User-Agent: NeoMutt/20180323 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 10:54 27/03, Darrick J. Wong wrote: > On Tue, Mar 26, 2019 at 02:02:50PM -0500, Goldwyn Rodrigues wrote: > > From: Goldwyn Rodrigues > > > > The IOMAP_F_COW is a flag to notify dax that it needs to copy > > the data from iomap->cow_addr to iomap->addr, if the start/end > > of I/O are not page aligned. > > > > This also introduces dax_to_dax_copy() which performs a copy > > from one part of the device to another, to a maximum of one page. > > > > Question: Using iomap.cow_addr == 0 means the CoW is to be copied > > (or memset) from a hole. Would this be better handled through a flag? > > > > Signed-off-by: Goldwyn Rodrigues > > --- > > fs/dax.c | 36 ++++++++++++++++++++++++++++++++++++ > > include/linux/iomap.h | 3 +++ > > 2 files changed, 39 insertions(+) > > > > diff --git a/fs/dax.c b/fs/dax.c > > index ca0671d55aa6..e254535dd830 100644 > > --- a/fs/dax.c > > +++ b/fs/dax.c > > @@ -1051,6 +1051,28 @@ static bool dax_range_is_aligned(struct block_device *bdev, > > return true; > > } > > > > +static void dax_to_dax_copy(struct iomap *iomap, loff_t pos, void *daddr, > > + size_t len) > > +{ > > + loff_t blk_start, blk_pg; > > + void *saddr; > > + ssize_t map_len; > > + > > + /* A zero address is a hole. */ > > + if (iomap->cow_addr == 0) { > > + memset(daddr, 0, len); > > + return; > > + } > > + > > + blk_start = iomap->cow_addr + pos - iomap->cow_pos; > > + blk_pg = round_down(blk_start, PAGE_SIZE); > > + > > + map_len = dax_direct_access(iomap->dax_dev, PHYS_PFN(blk_pg), PAGE_SIZE, > > + &saddr, NULL); > > + saddr += blk_start - blk_pg; > > + memcpy(daddr, saddr, len); > > +} > > + > > int __dax_zero_page_range(struct block_device *bdev, > > struct dax_device *dax_dev, sector_t sector, > > unsigned int offset, unsigned int size) > > @@ -1143,6 +1165,20 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data, > > break; > > } > > > > + if (iomap->flags & IOMAP_F_COW) { > > + loff_t pg_end = round_up(end, PAGE_SIZE); > > + /* > > + * Copy the first part of the page > > + * Note: we pass offset as length > > + */ > > + if (offset) > > + dax_to_dax_copy(iomap, pos - offset, kaddr, offset); > > + > > + /* Copy the last part of the range */ > > + if (end < pg_end) > > + dax_to_dax_copy(iomap, end, kaddr + offset + length, pg_end - end); > > + } > > + > > map_len = PFN_PHYS(map_len); > > kaddr += offset; > > map_len -= offset; > > diff --git a/include/linux/iomap.h b/include/linux/iomap.h > > index 0fefb5455bda..391785de1428 100644 > > --- a/include/linux/iomap.h > > +++ b/include/linux/iomap.h > > Probably a good idea to cc the iomap maintainers on this (entire > patchset)... Yup. Will include you and Christoph in the future iterations. This will not be the last iteration for this patchset. Looks like fsdevel and btrfs was too narrow a list ;) > > --D > > > @@ -35,6 +35,7 @@ struct vm_fault; > > #define IOMAP_F_NEW 0x01 /* blocks have been newly allocated */ > > #define IOMAP_F_DIRTY 0x02 /* uncommitted metadata */ > > #define IOMAP_F_BUFFER_HEAD 0x04 /* file system requires buffer heads */ > > +#define IOMAP_F_COW 0x08 /* cow before write */ > > > > /* > > * Flags that only need to be reported for IOMAP_REPORT requests: > > @@ -59,6 +60,8 @@ struct iomap { > > u64 length; /* length of mapping, bytes */ > > u16 type; /* type of mapping */ > > u16 flags; /* flags for mapping */ > > + u64 cow_addr; /* read address to perform CoW */ > > + loff_t cow_pos; /* file offset of cow_addr */ > > struct block_device *bdev; /* block device for I/O */ > > struct dax_device *dax_dev; /* dax_dev for dax operations */ > > void *inline_data; > > -- > > 2.16.4 > > > -- Goldwyn