linux-ext4 - Re: [PATCH 1/6] ext4: cache extent hole in extent status tree for ext4_da_map

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Date:	Mon, 24 Nov 2014 10:34:34 +0100
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
	Zheng Liu <gnehzuil.liu@...il.com>,
	Zheng Liu <wenqing.lz@...bao.com>,
	Andreas Dilger <adilger.kernel@...ger.ca>
Subject: Re: [PATCH 1/6] ext4: cache extent hole in extent status tree for
 ext4_da_map_blocks()

On Sun 23-11-14 00:43:35, Ted Tso wrote:
> On Fri, Nov 14, 2014 at 11:45:52AM +0100, Jan Kara wrote:
> > From: Zheng Liu <wenqing.lz@...bao.com>
> > 
> > Currently extent status tree doesn't cache extent hole when a write
> > looks up in extent tree to make sure whether a block has been allocated
> > or not.  In this case, we don't put extent hole in extent cache because
> > later this extent might be removed and a new delayed extent might be
> > added back.  But it will cause a defect when we do a lot of writes.  If
> > we don't put extent hole in extent cache, the following writes also need
> > to access extent tree to look at whether or not a block has been
> > allocated.  It brings a cache miss.  This commit fixes this defect.
> > Also if the inode doesn't have any extent, this extent hole will be
> > cached as well.
> > 
> > Cc: "Theodore Ts'o" <tytso@....edu>
> > Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> > Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
> > Signed-off-by: Jan Kara <jack@...e.cz>
> 
> This patch (either when applied alone, or as part of the entire patch
> series) is causing an xfstests regression test failure:
  I saw this in my testing as well but when investigating I somehow decided
it wasn't my bug and then forgot about it. Anyway, I'll check again and
resolve it either way.

								Honza

> FSTYP         -- ext4
> PLATFORM      -- Linux/i686 kvm-xfstests 3.18.0-rc3-00537-g932e3f9
> MKFS_OPTIONS  -- -q /dev/vdc
> MOUNT_OPTIONS -- -o acl,user_xattr -o block_validity /dev/vdc /vdc
> 
> ext4/003 4s ...	[00:14:39] [00:14:48] - output mismatch (see /results/results-4k/ext4/003.out.bad)
>     --- tests/ext4/003.out	2014-10-31 10:13:03.000000000 -0400
>     +++ /results/results-4k/ext4/003.out.bad	2014-11-23 00:14:48.935587897 -0500
>     @@ -1,3 +1,3 @@
>      QA output created by 003
>     -wrote 268435456/268435456 bytes at offset 0
>     +wrote 241762304/268435456 bytes at offset 0
>      XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
>     ...
>     (Run 'diff -u tests/ext4/003.out /results/results-4k/ext4/003.out.bad'  to see the entire diff)
> 
> 				- Ted
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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