linux-ext4 - Re: [PATCH 04/10 v5] ext4: track all extent status in extent status tree

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Date:	Fri, 15 Feb 2013 14:53:35 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>,
	Jan kara <jack@...e.cz>
Subject: Re: [PATCH 04/10 v5] ext4: track all extent status in extent status
 tree

On Tue, Feb 12, 2013 at 10:28:19PM -0500, Theodore Ts'o wrote:
> On Fri, Feb 08, 2013 at 04:44:00PM +0800, Zheng Liu wrote:
> > From: Zheng Liu <wenqing.lz@...bao.com>
> > 
> > By recording the phycisal block and status, extent status tree is able
> > to track the status of every extents.  When we call _map_blocks
> > functions to lookup an extent or create a new written/unwritten/delayed
> > extent, this extent will be inserted into extent status tree.  The hole
> > extent is inserted in ext4_ext_put_gap_in_cache().  If there is no any
> > extent, we will not insert a hole extent [0, ~0] into the extent status
> > tree in order to reduce the complextiy of code.
> > 
> > We don't load all extents from disk in alloc_inode() because it costs
> > too much memory, and if a file is opened and closed frequently it will
> > takes too much time to load all extent information.  So currently when
> > we create/lookup an extent, this extent will be inserted into extent
> > status tree.  Hence, the extent status tree may not comprehensively
> > contain all of the extents found in the file.
> > 
> > Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
> > Cc: "Theodore Ts'o" <tytso@....edu>
> > Cc: Jan kara <jack@...e.cz>
> 
> Unfortunately, this commit is apparently causing test failures with
> bigalloc:
> 
> --- 013.out	2013-01-01 22:52:04.000000000 -0500
> +++ 013.out.bad	2013-02-12 22:08:47.110766615 -0500
> @@ -8,7 +8,4 @@
>  -----------------------------------------------
>  fsstress.2 : -p 20 -r
>  -----------------------------------------------
> -
> ------------------------------------------------
> -fsstress.3 : -p 4 -z -f rmdir=10 -f link=10 -f creat=10 -f mkdir=10 -f rename=30 -f stat=30 -f unlink=30 -f truncate=20
> ------------------------------------------------
> +_check_generic_filesystem: filesystem on /dev/vdd is inconsistent (see 013.full)
> _check_generic_filesystem: filesystem on /dev/vdd is inconsistent (see 013.full)
> Ran: 013
> Failures: 013
> Failed 1 of 1 tests
> END TEST: Ext4 4k block w/bigalloc Tue Feb 12 22:08:49 EST 2013
> e2fsck 1.43-WIP (15-Jan-2013)
> Pass 1: Checking inodes, blocks, and sizes
> Inode 618, i_blocks is 1408, should be 1536.  Fix? yes
> 
> Pass 2: Checking directory structure
> Pass 3: Checking directory connectivity
> Pass 4: Checking reference counts
> Pass 5: Checking group summary information
> 
> /dev/vdd: ***** FILE SYSTEM WAS MODIFIED *****
> /dev/vdd: 3969/81936 files (13.1% non-contiguous), 176208/1310720 blocks
> 
> 
> I haven't been able to figure out what is going on here, but if we
> can't figure this out I may need to push off this patch series to the
> next merge window.  I've tried splitting up this patch into two pieces
> to make it clearer what is going on, but I still can't see how this
> would be affecting the i_blocks calculation.

Hi Ted,

Oops, I run xfstests #13 serveral times and this bug can be triggered.
Sorry about that.  I will look at it, but I am not sure whether it can
be fixed before merge window opens.  Thanks for let me know.

For this bug, I guess that the problem is in ext4_da_invalidatepages()
because when a file is truncated this function will be called.  But it
seems that the delay space reservation is the root cause.  Ah, let me
trace it.

Regards,
                                                - Zheng
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