linux-ext4 - Re: Why does not freeblocks number change after deleting a big file?

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Message-ID: <20140506095748.GD23108@azat>
Date:	Tue, 6 May 2014 13:57:48 +0400
From:	Azat Khuzhin <a3at.mail@...il.com>
To:	Younger Liu <younger.liucn@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Why does not freeblocks number change after deleting a big file?

On Tue, May 06, 2014 at 11:32:12AM +0800, Younger Liu wrote:
> Hi:
>   Analyze ext4 filesystem with "debugfs -R "stats" <device>",
> Why does not free blocks number change after deleting a big file?
> 
> The big file:
> # stat test
>   file："test"
>   size：290554084       blocks：567496     IO block：4096
> 
> before deleting the file "test":
> # debugfs -R "stats" /dev/sdb
> ...
> Inode count:              243593216
> Block count:              1948728320
> Reserved block count:     97436416
> Free blocks:              406830314
> Free inodes:              151667854
> ...
> 
> deleting the file "test"
> # debugfs -R "stats" /dev/sdb
> ...
> Inode count:              243593216
> Block count:              1948728320
> Reserved block count:     97436416
> Free blocks:              406830314
> Free inodes:              151667854

Hi,

Seems that you are trying to do this on a mounted partition, and the
super block are not dumped to disk after every write/flush.

You could use statfs(2) instead of debugfs/stats command, or "mount -o
remount /dev/sdb_X_" and after debugfs, this _must_ work only in case
you don't have journal.

For more information you could look into ext4_commit_super().

> ...
> 
>      Younger
>      thx.
> --
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-- 
Respectfully
Azat Khuzhin
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