linux-ext4 - Re: [PATCH v4 2/8] ext4: move out IOMAP

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Date:   Wed, 9 Oct 2019 20:31:46 +1100
From:   Matthew Bobrowski <mbobrowski@...browski.org>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     tytso@....edu, jack@...e.cz, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: Re: [PATCH v4 2/8] ext4: move out IOMAP_WRITE path into separate
 helper

On Wed, Oct 09, 2019 at 11:52:41AM +0530, Ritesh Harjani wrote:
> On 10/3/19 5:03 PM, Matthew Bobrowski wrote:
> Minor comment, but otherwise.
> Patch looks good to me. You may add:
> 
> Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>

*nod* - Thank you!

> >   static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> >   			    unsigned flags, struct iomap *iomap)
> >   {
> > @@ -3500,62 +3556,16 @@ 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, flags, first_block, &map);
> 
> We don't need "first_block" argument here. Since
> map->m_lblk saves first_block directly above in the same function.

You're right. I will change that.

> No strong objection against ext4_iomap_alloc, but
> maybe ext4_iomap_map_write sounds better?
> Either way is fine though.

I like 'ext4_iomap_alloc', because it's performing allocation in
preparation for a write being performed on behalf of iomap. :)

--<M>--