From: Markus Trippelsdorf <markus@trippelsdorf.de>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)
Date: Thu, 14 Apr 2011 18:03:43 +0200
Message-ID: <20110414160343.GA12787@x4.trippels.de>
References: <20110414102608.GA1678@x4.trippels.de>
 <20110414120635.GB1678@x4.trippels.de>
 <20110414140222.GB1679@x4.trippels.de>
 <4DA70BD3.1070409@draigBrady.com>
 <4DA717B2.3020305@sandeen.net>
 <4DA7182B.8050409@draigBrady.com>
 <4DA71920.9@sandeen.net>
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Cc: =?iso-8859-1?Q?P=E1draig?= Brady <P@draigBrady.com>,
	xfs-oss <xfs@oss.sgi.com>, linux-ext4@vger.kernel.org,
	coreutils@gnu.org
To: Eric Sandeen <sandeen@sandeen.net>
Content-Disposition: inline
In-Reply-To: <4DA71920.9@sandeen.net>
Sender: linux-ext4-owner@vger.kernel.org

On 2011.04.14 at 10:56 -0500, Eric Sandeen wrote:
> On 4/14/11 10:52 AM, P=E1draig Brady wrote:
> > On 14/04/11 16:50, Eric Sandeen wrote:
> >> On 4/14/11 9:59 AM, P=E1draig Brady wrote:
> >>> On 14/04/11 15:02, Markus Trippelsdorf wrote:
> >>>>>> Hi P=E1draig,
> >>>>>>
> >>>>>> here you go:
> >>>>>> + filefrag -v unwritten.withdata                              =
                                                                       =
               =20
> >>>>>> Filesystem type is: ef53                                      =
                                                                       =
               =20
> >>>>>> File size of unwritten.withdata is 5120 (2 blocks, blocksize 4=
096)                                                                   =
               =20
> >>>>>>  ext logical physical expected length flags                   =
                                                                       =
               =20
> >>>>>>    0       0   274432            2560 unwritten,eof           =
                                                                       =
               =20
> >>>>>> unwritten.withdata: 1 extent found
> >>>>>>
> >>>>>> Please notice that this also happens with ext4 on the same ker=
nel.=20
> >>>>>> Btrfs is fine.
> >>>>>
> >>>> `filefrag -vs` fixes the issue on both xfs and ext4.
> >>>
> >>> So in summary, currently on (2.6.39-rc3), the following
> >>> will (usually?) report a single unwritten extent,
> >>> on both ext4 and xfs
> >>>
> >>>   fallocate -l 10MiB -n k
> >>>   dd count=3D10 if=3D/dev/urandom conv=3Dnotrunc iflag=3Dfullbloc=
k of=3Dk
> >>>   filefrag -v k # grep for an extent without unwritten || fail
> >>
> >> right, that's what I see too in testing.
> >>
> >> But would the coreutils install have done a preallocation of the d=
estination file?
> >>
> >> Otherwise this looks like a different bug...
> >>
> >>> This particular issue has been discussed so far at:
> >>> http://debbugs.gnu.org/cgi/bugreport.cgi?bug=3D8411
> >>> Note there it was stated there that ext4 had this
> >>> fixed as of 2.6.39-rc1, so maybe there is something lurking?
> >>
> >> ext4 got a fix, but not xfs, I guess.  My poor brain can't remembe=
r, I think I started looking into it, but it's clearly still broken.
> >>
> >> Still, I don't know for sure what happened to Markus - did somethi=
ng preallocate, in his case?
> >=20
> > Well that preallocate test is failing for him
> > when the source file is either on ext4 or xfs.
> > He noticed the issue initially on XFS when copying
> > none preallocated files, so XFS probably just has
> > the general issue of needing a sync before fiemap,
> > where as EXT4 just has this preallocate one
> > (though I've not seen it myself).
> >=20
> > cheers,
> > P=E1draig.
> >=20
>=20
> well, if I simply take the preallocation step out of the testcase, it=
 works fine on xfs without a sync.
>=20
> So I still don't know what Markus hit...

Maybe it's delalloc:

x4 /tmp # dd count=3D10 if=3D/dev/urandom conv=3Dnotrunc iflag=3Dfullbl=
ock of=3Dk                                                             =
                 =20
10+0 records in
10+0 records out
5120 bytes (5.1 kB) copied, 0.0021822 s, 2.3 MB/s
x4 /tmp # filefrag -v k=20
=46ilesystem type is: 58465342
=46ile size of k is 5120 (2 blocks, blocksize 4096)
 ext logical physical expected length flags
   0       0        0              16 unknown,delalloc,eof
k: 1 extent found
x4 /tmp # sync
x4 /tmp # filefrag -v k=20
=46ilesystem type is: 58465342
=46ile size of k is 5120 (2 blocks, blocksize 4096)
 ext logical physical expected length flags
   0       0 26960045              16 eof
k: 1 extent found

--=20
Markus
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