linux-ext4 - Re: [PATCH 4/4] ext4: fix suboptimal seek

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Date:	Fri, 12 Dec 2014 11:52:29 +0300
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4] ext4: fix suboptimal seek_{data,hole} extents traversial

Theodore Ts'o <tytso@....edu> writes:

> Hi Dmitry,
>
> I only noticed this after I sent the pull request to Linus, but it
> looks like this patch is triggering regression using the ext3 config:
>
> ./kvm-xfstests -c ext3 generic/285:
>
> The failure reported by seek_santy_test is:
>
> 10. Test a huge file for offset overflow
> 10.01 SEEK_HOLE expected 65536 or 0, got 0.                       FAIL
> 10.02 SEEK_HOLE expected 65536 or 0, got 1.                       FAIL
> 10.03 SEEK_DATA expected 0 or 0, got -1.                          FAIL
> 10.04 SEEK_DATA expected 1 or 1, got -1.                          FAIL
> 10.05 SEEK_HOLE expected 0 or 0, got -65536.                      FAIL
> 10.06 SEEK_DATA expected -65536 or -65536, got -1.                FAIL
> 10.07 SEEK_DATA expected -65535 or -65535, got -1.                FAIL
> 10.08 SEEK_DATA expected -65536 or -65536, got -1.                FAIL
>
> What's strange is that if I run the commands by hand, I get a very
> different failure:
>
> root@...-xfstests:~# ./xfstests/src/seek_sanity_test /vdd/seek_sanity_testfile
> File system magic#: 0xef53
> Allocation size: 4096
> Kernel does not support llseek(2) extensions SEEK_HOLE and/or SEEK_DATA. Aborting.
>
> Using strace, the problem is that the SEEK_DATA fallocate is failing:
>
> pwrite64(3, "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"..., 8192, 0) = 8192
> ftruncate64(3, 16384)                   = 0
> _llseek(3, 0, 0xbff7fe70, SEEK_DATA)    = -1 ENXIO (No such device or address)
Oh. Indeed That is my mistake.

ret = ext4_fiemap(inode, &fie, offset, maxsize - offset);
/* No extents found, EOF */
if (!fie.fi_extents_mapped) {
     ret = -ENXIO;
     break;
  }                                                                           
Delalloc case handled incorrectly. Will fix that ASAP.

>
> This fails with commit 14516bb: "ext4: fix suboptimal seek_{data,hole}
> extents traversial" and succeeds with its immediate predesssor commit.
>
> I've tried looking at this, but hte fact that I'm seeing different
> results when I run it by hand (sometimes I can trigger the failure
> with runtests.sh, usually I can't), means that it appears to be timing
> dependent.
>
> Could you take a look?
>
> Many thanks!!
>
> 						- Ted
> --
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