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

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH, RFC] xfs: add heuristic to flush on rename
From: Eric Sandeen <sandeen@xxxxxxxxxx>
Date: Fri, 25 Apr 2014 14:59:25 -0500
Cc: xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140425195528.GA16567@xxxxxxxxxxxxx>
References: <535ABA9D.2060305@xxxxxxxxxx> <20140425195528.GA16567@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.4.0
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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