From: Andreas Dilger <andreas.dilger@oracle.com>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: linux-ext4@vger.kernel.org
Subject: Re: FIEMAP sometimes returns bad information for delalloc extents
Date: Sat, 27 Mar 2010 11:52:56 -0600 [thread overview]
Message-ID: <DB0601D5-963C-4017-B7EA-A3764D2067EF@oracle.com> (raw)
In-Reply-To: <E1NvXbm-00087i-Tf@closure.thunk.org>
On 2010-03-27, at 09:07, Theodore Ts'o wrote:
> I was monitoring the progress of a distributed download program, and
> saw
> the following output from two runs of filefrag taken a few seconds
> apart:
>
> 8 790 8825663 8825551 65
> 9 855 0 8825727 319 unknown,delalloc
> 10 1174 8798367 318 128
>
> 7 790 8825663 8825559 69
> 8 1174 8798367 8825731 128
>
> The length of the delalloc extent, 319, is bogus. The 319 seems to
> come
> from 1174 - 855. But it's not actually the number of delayed
> allocation blocks, as we can see when the blocks finally get written;
> apparently it was only 4 blocks long.
I'm surprised it shows anything at all for delalloc blocks, since
AFAIK FIEMAP is only walking the extent tree. It would be interesting
if it walked the VM pagetable for unallocated extents in the file, and
beyond i_size.
> I don't have time to try to track this down just now, and it's not all
> that serious a bug since delalloc regions are by definition highly
> transient, but it does look like we have a bug here.
Cheers, Andreas
--
Andreas Dilger
Principal Engineer, Lustre Group
Oracle Corporation Canada Inc.
next prev parent reply other threads:[~2010-03-27 17:54 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-27 15:07 FIEMAP sometimes returns bad information for delalloc extents Theodore Ts'o
2010-03-27 17:52 ` Andreas Dilger [this message]
2010-03-27 18:35 ` Eric Sandeen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=DB0601D5-963C-4017-B7EA-A3764D2067EF@oracle.com \
--to=andreas.dilger@oracle.com \
--cc=linux-ext4@vger.kernel.org \
--cc=tytso@mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).