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Date: Wed, 23 Oct 2019 12:07:16 +0530
From: Ritesh Harjani <riteshh@...ux.ibm.com>
To: Matthew Bobrowski <mbobrowski@...browski.org>, tytso@....edu,
jack@...e.cz, adilger.kernel@...ger.ca
Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: Re: [PATCH v5 03/12] ext4: split IOMAP_WRITE branch in
ext4_iomap_begin() into helper
On 10/21/19 2:48 PM, Matthew Bobrowski wrote:
> In preparation for porting across the ext4 direct I/O path for reads
> and writes over to the iomap infrastructure, split up the IOMAP_WRITE
> chunk of code into a separate helper ext4_alloc_iomap(). This way,
> when we add the necessary bits for direct I/O, we don't end up with
> ext4_iomap_begin() becoming a behemoth twisty maze.
>
> Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>
Patch looks good to me. You may add:
Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> ---
> fs/ext4/inode.c | 112 ++++++++++++++++++++++++++----------------------
> 1 file changed, 60 insertions(+), 52 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 0dd29ae5cc8c..3dc92bd8a944 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3442,6 +3442,62 @@ static void ext4_set_iomap(struct inode *inode, struct iomap *iomap,
> }
> }
>
> +static int ext4_iomap_alloc(struct inode *inode, struct ext4_map_blocks *map,
> + unsigned int flags)
> +{
> + handle_t *handle;
> + u8 blkbits = inode->i_blkbits;
> + int ret, dio_credits, retries = 0;
> +
> + /*
> + * Trim the mapping request to the maximum value that we can map at
> + * once for direct I/O.
> + */
> + if (map->m_len > DIO_MAX_BLOCKS)
> + map->m_len = DIO_MAX_BLOCKS;
> + dio_credits = ext4_chunk_trans_blocks(inode, map->m_len);
> +
> +retry:
> + /*
> + * Either we allocate blocks and then don't get an unwritten extent, so
> + * in that case we have reserved enough credits. Or, the blocks are
> + * already allocated and and unwritten. In that case, the extent
> + * conversion fits into the credits too.
> + */
> + handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS, dio_credits);
> + if (IS_ERR(handle))
> + return PTR_ERR(handle);
> +
> + ret = ext4_map_blocks(handle, inode, map, EXT4_GET_BLOCKS_CREATE_ZERO);
> + if (ret < 0)
> + goto journal_stop;
> +
> + /*
> + * If we have allocated blocks beyond EOF, we need to ensure that
> + * they're truncated if we crash before updating the inode size
> + * metadata within ext4_iomap_end(). For faults, we don't need to do
> + * that (and cannot due to the orphan list operations needing an
> + * inode_lock()). If we happen to instantiate blocks beyond EOF, it is
> + * because we race with a truncate operation, which already has added
> + * the inode onto the orphan list.
> + */
> + if (!(flags & IOMAP_FAULT) && map->m_lblk + map->m_len >
> + (i_size_read(inode) + (1 << blkbits) - 1) >> blkbits) {
> + int err;
> +
> + err = ext4_orphan_add(handle, inode);
> + if (err < 0)
> + ret = err;
> + }
> +
> +journal_stop:
> + ext4_journal_stop(handle);
> + if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
> + goto retry;
> +
> + return ret;
> +}
> +
> static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> unsigned flags, struct iomap *iomap)
> {
> @@ -3502,62 +3558,14 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> }
> }
> } else if (flags & IOMAP_WRITE) {
> - int dio_credits;
> - handle_t *handle;
> - int retries = 0;
> -
> - /* Trim mapping request to maximum we can map at once for DIO */
> - if (map.m_len > DIO_MAX_BLOCKS)
> - map.m_len = DIO_MAX_BLOCKS;
> - dio_credits = ext4_chunk_trans_blocks(inode, map.m_len);
> -retry:
> - /*
> - * Either we allocate blocks and then we don't get unwritten
> - * extent so we have reserved enough credits, or the blocks
> - * are already allocated and unwritten and in that case
> - * extent conversion fits in the credits as well.
> - */
> - handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS,
> - dio_credits);
> - if (IS_ERR(handle))
> - return PTR_ERR(handle);
> -
> - ret = ext4_map_blocks(handle, inode, &map,
> - EXT4_GET_BLOCKS_CREATE_ZERO);
> - if (ret < 0) {
> - ext4_journal_stop(handle);
> - if (ret == -ENOSPC &&
> - ext4_should_retry_alloc(inode->i_sb, &retries))
> - goto retry;
> - return ret;
> - }
> -
> - /*
> - * If we added blocks beyond i_size, we need to make sure they
> - * will get truncated if we crash before updating i_size in
> - * ext4_iomap_end(). For faults we don't need to do that (and
> - * even cannot because for orphan list operations inode_lock is
> - * required) - if we happen to instantiate block beyond i_size,
> - * it is because we race with truncate which has already added
> - * the inode to the orphan list.
> - */
> - if (!(flags & IOMAP_FAULT) && first_block + map.m_len >
> - (i_size_read(inode) + (1 << blkbits) - 1) >> blkbits) {
> - int err;
> -
> - err = ext4_orphan_add(handle, inode);
> - if (err < 0) {
> - ext4_journal_stop(handle);
> - return err;
> - }
> - }
> - ext4_journal_stop(handle);
> + ret = ext4_iomap_alloc(inode, &map, flags);
> } else {
> ret = ext4_map_blocks(NULL, inode, &map, 0);
> - if (ret < 0)
> - return ret;
> }
>
> + if (ret < 0)
> + return ret;
> +
> ext4_set_iomap(inode, iomap, &map, offset, length);
> if (delalloc && iomap->type == IOMAP_HOLE)
> iomap->type = IOMAP_DELALLOC;
>
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