From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Goldwyn Rodrigues <rgoldwyn@suse.de>
Cc: linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Goldwyn Rodrigues <rgoldwyn@suse.com>
Subject: Re: [PATCH 04/15] dax: Introduce IOMAP_F_COW for copy-on-write
Date: Wed, 27 Mar 2019 10:54:14 -0700 [thread overview]
Message-ID: <20190327175414.GB1172@magnolia> (raw)
In-Reply-To: <20190326190301.32365-5-rgoldwyn@suse.de>
On Tue, Mar 26, 2019 at 02:02:50PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
>
> 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 <rgoldwyn@suse.com>
> ---
> 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)... <cough>
--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
>
next prev parent reply other threads:[~2019-03-27 17:54 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190326190301.32365-1-rgoldwyn@suse.de>
2019-03-26 19:02 ` [PATCH 01/15] btrfs: create a mount option for dax Goldwyn Rodrigues
2019-03-26 19:10 ` Matthew Wilcox
2019-03-27 11:00 ` Goldwyn Rodrigues
2019-03-27 12:00 ` Matthew Wilcox
2019-03-27 12:26 ` Goldwyn Rodrigues
2019-03-27 23:31 ` Goldwyn Rodrigues
2019-03-27 17:38 ` Adam Borowski
2019-03-28 14:49 ` David Sterba
2019-03-28 17:28 ` David Sterba
2019-03-28 17:57 ` Darrick J. Wong
2019-04-01 20:43 ` Goldwyn Rodrigues
2019-03-26 19:02 ` [PATCH 02/15] btrfs: Carve out btrfs_get_extent_map_write() out of btrfs_get_blocks_write() Goldwyn Rodrigues
2019-03-26 19:02 ` [PATCH 03/15] btrfs: basic dax read Goldwyn Rodrigues
2019-03-26 19:02 ` [PATCH 04/15] dax: Introduce IOMAP_F_COW for copy-on-write Goldwyn Rodrigues
2019-03-27 17:54 ` Darrick J. Wong [this message]
2019-03-27 18:58 ` Goldwyn Rodrigues
2019-03-28 14:45 ` Darrick J. Wong
2019-04-01 4:38 ` Dave Chinner
2019-04-01 21:41 ` Goldwyn Rodrigues
2019-04-01 23:06 ` Dave Chinner
2019-04-03 1:56 ` Goldwyn Rodrigues
2019-04-03 3:20 ` Dave Chinner
2019-04-07 7:26 ` Christoph Hellwig
2019-03-26 19:02 ` [PATCH 05/15] btrfs: return whether extent is nocow or not Goldwyn Rodrigues
2019-03-31 18:42 ` Nikolay Borisov
2019-03-26 19:02 ` [PATCH 06/15] btrfs: Rename __endio_write_update_ordered() to btrfs_update_ordered_extent() Goldwyn Rodrigues
2019-03-26 19:02 ` [PATCH 07/15] btrfs: add dax write support Goldwyn Rodrigues
2019-03-28 14:53 ` Darrick J. Wong
2019-04-01 20:39 ` Goldwyn Rodrigues
2019-03-26 19:02 ` [PATCH 08/15] dax: add dax_iomap_cow to copy a mmap page before writing Goldwyn Rodrigues
2019-03-28 15:41 ` Darrick J. Wong
2019-03-26 19:02 ` [PATCH 09/15] btrfs: add dax mmap support Goldwyn Rodrigues
2019-03-28 15:45 ` Darrick J. Wong
2019-03-26 19:02 ` [PATCH 10/15] btrfs: Add dax specific address_space_operations Goldwyn Rodrigues
2019-03-26 19:02 ` [PATCH 11/15] fs: dedup file range to use a compare function Goldwyn Rodrigues
2019-03-28 17:04 ` Darrick J. Wong
2019-04-01 20:36 ` Goldwyn Rodrigues
2019-03-26 19:02 ` [PATCH 12/15] btrfs: trace functions for btrfs_iomap_begin/end Goldwyn Rodrigues
2019-03-26 19:02 ` [PATCH 13/15] btrfs: handle dax page zeroing Goldwyn Rodrigues
2019-03-26 19:03 ` [PATCH 14/15] btrfs: Disable dax-based defrag and send Goldwyn Rodrigues
2019-03-26 19:03 ` [PATCH 15/15] btrfs: Writeprotect mmap pages on snapshot Goldwyn Rodrigues
2019-03-28 15:48 ` Darrick J. Wong
2019-03-26 19:09 ` [PATCH v2 00/15] btrfs dax support Goldwyn Rodrigues
2019-03-27 20:14 ` Adam Borowski
2019-03-27 23:26 ` Goldwyn Rodrigues
2019-03-28 10:24 ` [PATCH] btrfs: allow MAP_SYNC mmap Adam Borowski
2019-03-28 10:42 ` Adam Borowski
2019-04-01 20:08 ` Goldwyn Rodrigues
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