From: "Takashi Sato" <sho@tnes.nec.co.jp>
Subject: Re: Online defragmentation
Date: Thu, 31 May 2007 13:05:06 +0900
Message-ID: <00c201c7a338$e238ae50$4168010a@bsd.tnes.nec.co.jp>
References: <465D2202.60600@linux.vnet.ibm.com> <465D2C37.9080905@linux.vnet.ibm.com>
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Cc: "linux-ext4" <linux-ext4@vger.kernel.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Sender: linux-ext4-owner@vger.kernel.org

Hi,

>> I was looking at online defrag code and found that the tmp_inode is created with 
>> tmp_inode->i_nlink equal to zero. Now i am not sure whether i understand the code 
>> correctly, but AFAIU we allocate contiguous block using this tmp_inode. That means 
>> tmp_inode have extent details corresponding to the blocks. Now we are mapping the file 
>> data found in the original inode to this new blocks. Towards the end we does a iput. In 
>> iput since we have i_nlink as zero it will go ahead and call generic_delete_inode which 
>> will cause these data blocks to be marked free (right ?)
>>
>
> Looking at the code again i guess for defragmentation it is okey. I guess what actually 
> happens is the blocks that is corresponding to the original inode get accounted under 
> tmp_inode. (it actually does a swap of blocks ) So doing a iput with i_nlink = 0 is the 
> correct approach.
>
> Correct me if i am wrong.

Your understanding is right.
The iput() is called to free the old blocks which were in the original
inode.

Cheers, Takashi