Re: [PATCH, RFC] xfs: add heuristic to flush on rename

[Eric Sandeen <sandeen@redhat.com>]

On 4/25/14, 2:55 PM, Christoph Hellwig wrote:
>> +	/*
>> +	 * If we are renaming a just-written file over an existing
>> +	 * file, be pedantic and flush it out if it looks like somebody
>> +	 * is doing a tmpfile dance, and didn't fsync.  Best effort;
>> +	 * ignore errors.
>> +	 */
>> +	if (new_inode) {
>> +		xfs_inode_t *ip = XFS_I(odentry->d_inode);
>> +
>> +		if (VN_DIRTY(VFS_I(ip)) && ip->i_delayed_blks > 0)
>> +			filemap_flush(new_inode->i_mapping);
>> +	}
> 
> IFF we want a heuristic it should be a proper filemap_write_and_wait.  a
> non-blocking start of I/O without waiting for it is snake oil.

Hi Christoph -

It's the same thing we do on truncated and written files, FWIW:

                truncated = xfs_iflags_test_and_clear(ip, XFS_ITRUNCATED);
                if (truncated) {
                        xfs_iflags_clear(ip, XFS_IDIRTY_RELEASE);
                        if (VN_DIRTY(VFS_I(ip)) && ip->i_delayed_blks > 0) {
                                error = -filemap_flush(VFS_I(ip)->i_mapping);
                                if (error)
                                        return error;
                        }
                }

and that's served us pretty well in the past years.

I don't know if we're looking for rock-solid guarantees, or just do a little
to try to save the user from themselves... blocking would make this a lot more
heavyweight I suppose.  Just depends on what we are willing / trying to do.

thanks,
-Eric

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