From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Online defragmentation
Date: Wed, 30 May 2007 12:34:34 +0530
Message-ID: <465D2202.60600@linux.vnet.ibm.com>
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Cc: linux-ext4 <linux-ext4@vger.kernel.org>
To: Takashi Sato <sho@tnes.nec.co.jp>
Sender: linux-ext4-owner@vger.kernel.org

Hi Takashi,

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 ?)


I haven't tested the defrag code. This came up when i was doing the 
online migration. With large file having large number of fragmented 
blocks I was getting the below error during the iput of the temporary 
inode.

"ext4_free_blocks Freeing blocks not in datazone ...."

I was able to fix that by setting i_nlink = 1 which will cause the 
generic_forget_inode to be called


-aneesh