linux-ext4 - Re: [PATCH v3 2/6] ext4: move inode extension/truncate code out from ext4_iomap

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Date:   Tue, 24 Sep 2019 15:13:43 +0200
From:   Jan Kara <jack@...e.cz>
To:     Matthew Bobrowski <mbobrowski@...browski.org>
Cc:     tytso@....edu, jack@...e.cz, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        david@...morbit.com, hch@...radead.org, darrick.wong@...cle.com
Subject: Re: [PATCH v3 2/6] ext4: move inode extension/truncate code out from
 ext4_iomap_end()

On Mon 23-09-19 18:21:15, Jan Kara wrote:
> On Thu 12-09-19 21:04:00, Matthew Bobrowski wrote:
> So I'd just call ext4_handle_inode_extension() unconditionally like:
> 
> 	error = ext4_handle_inode_extension(inode, offset, ret, len);
> 
> and have a quick check at the beginning of that function to avoid starting
> transaction when there isn't anything to do. Something like:
> 
> 	/*
> 	 * DIO and DAX writes get exclusion from truncate (i_rwsem) and
> 	 * page writeback (i_rwsem and flushing all dirty pages).
> 	 */
> 	WARN_ON_ONCE(i_size_read(inode) != EXT4_I(inode)->i_disksize);
> 	if (offset + count <= i_size_read(inode))
> 		return 0;

One correction here. With commit 45d8ec4d9fd54 in mind this should be:

 	/*
 	 * DIO and DAX writes get exclusion from truncate (i_rwsem). There
 	 * can be pending delalloc writeback beyond the range written by
 	 * DIO though.
 	 */
 	WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize);
 	if (offset + count <= EXT4_I(inode)->i_disksize)
 		return 0;

								Honza

> 	if (len < 0)
> 		goto truncate;
> 
> 	... do the heavylifting with transaction start, inode size update,
> 	and orphan handling...
> 
> 	if (truncate) {
> truncate:
> 		ext4_truncate_failed_write(inode);
> orphan_del:
> 		/*
> 		 * If the truncate operation failed early the inode
> 		 * may still be on the orphan list. In that case, we
> 		 * need try remove the inode from the linked list in
> 		 * memory.
> 		 */
> 		if (inode->i_nlink)
> 			ext4_orphan_del(NULL, inode);
> 	}
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR