Loop devices act strangely in 2.6.35
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https://bugzilla.kernel.org/show_bug.cgi?id=16380
Artem S. Tashkinov <[email protected]> changed:
What |Removed |Added
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Component|Block Layer |ext2
AssignedTo|[email protected] |[email protected]
| |g
Product|IO/Storage |File System--- Comment #8 from Artem S. Tashkinov <[email protected]> 2011-03-22 22:02:54 --- This is an ext2 fs bug.
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[Bug 16380] ext2 driver "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
Artem S. Tashkinov <[email protected]> changed:
What |Removed |Added
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Summary|Loop devices act strangely |ext2 driver "hangs" for a
|in 2.6.35 |few seconds when trying to
| |write a lot of data to a
| |freshly RW mounted FSSignature · 3 lines
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
Artem S. Tashkinov <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|ext2 |ext4
AssignedTo|[email protected] |[email protected]
|g |g
Summary|ext2 driver "hangs" for a |ext2/ext4 filesystem
|few seconds when trying to |"hangs" for a few seconds
|write a lot of data to a |when trying to write a lot
|freshly RW mounted FS |of data to a freshly RW
| |mounted FSSignature · 3 lines
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
--- Comment #9 from Artem S. Tashkinov <[email protected]> 2012-08-04 11:19:36 --- It's reproducible with ext4fs as well under Linux 3.5.
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
Prashant Shah <[email protected]> changed:
What |Removed |Added
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CC| |[email protected]
--- Comment #10 from Prashant Shah <[email protected]> 2012-08-04 11:53:19 --- Didnt face this issue with 3.2.0-23-generic - 64 bit.
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
--- Comment #11 from Prashant Shah <[email protected]> 2012-08-04 12:16:16 --- (In reply to comment #10)
Quoted 1 line
Didnt face this issue with 3.2.0-23-generic - 64 bit.
Sorry I was able to reproduce it under 3.2.0-23-generic - 64 bit
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
Artem S. Tashkinov <[email protected]> changed:
What |Removed |Added
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Kernel Version|2.6.35 |2.6.x 3.x
Regression|Yes |NoSignature · 3 lines
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
--- Comment #12 from Theodore Tso <[email protected]> 2012-08-04 18:13:20 --- I wasn't able to duplicate this with an underlying ext4 file system, with the loop file system being ext2, using a 3.5 kernel on a system with 16G.
I tried both using a variety of small and medium sized files, as well as one very large file, and I didn't see any unexplained stuttering in write
bandwidth. (There were times when cp -r was clearly writing to the in-memory
page cache, and the writeback hadn't begone yet. There were also times when
we couldn't do any more writing, because we were busy reading from the source drive. But it all looked pretty normal to me.)
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
--- Comment #13 from Theodore Tso <[email protected]> 2012-08-04 18:14:08 --- BTW, I was using iostat 1 to measure I/O activity. Call me old-school; I don't exactly trust GUI tools. :-)
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
--- Comment #14 from Artem S. Tashkinov <[email protected]> 2012-08-04 18:51:24 --- (In reply to comment #12)
Quoted 9 lines
I wasn't able to duplicate this with an underlying ext4 file system, with the loop file system being ext2, using a 3.5 kernel on a system with 16G.
I tried both using a variety of small and medium sized files, as well as one very large file, and I didn't see any unexplained stuttering in write
bandwidth. (There were times when cp -r was clearly writing to the in-memory
page cache, and the writeback hadn't begone yet. There were also times when
we couldn't do any more writing, because we were busy reading from the source drive. But it all looked pretty normal to me.)
Hm, I cannot reproduce the problem with a loop device on top of tmpfs either, but I've just checked my 250GB ext4 partition and the bug is still there:
When I try to copy a 3GB file (residing in tmpfs so it's all cached) to it, there's a 4 (four) seconds delay before a single byte gets written to the destination partition. After that all consequent files get written without any delays.
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
--- Comment #15 from Theodore Tso <[email protected]> 2012-08-04 19:51:51 --- The delay before the write starts is normal; that's encoded in how the writeback code handles dirty pages. We don't start writes the instant that pages are dirtied in the buffer cache.
In any case, if you have arguments about how the writeback code makes its choices, it's kinda of pointless to be complaining on a bug targetted at the ext4 developers, since we start the writeback when the VM system asks us to start write pages belonging to a particular inode....
See /usr/src/linux/Documentation/sysctl/vm.txt for more information.
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
Artem S. Tashkinov <[email protected]> changed:
What |Removed |Added
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Status|NEW |RESOLVED
Resolution| |INVALID--- Comment #16 from Artem S. Tashkinov <[email protected]> 2012-08-04 20:00:28 --- (In reply to comment #15)
Quoted 10 lines
The delay before the write starts is normal; that's encoded in how the writeback code handles dirty pages. We don't start writes the instant that pages are dirtied in the buffer cache.
In any case, if you have arguments about how the writeback code makes its choices, it's kinda of pointless to be complaining on a bug targetted at the ext4 developers, since we start the writeback when the VM system asks us to start write pages belonging to a particular inode....
See
/usr/src/linux/Documentation/sysctl/vm.txtfor more information.
Thanks for letting us know, probably what I perceived as a regression in ext4fs was in fact a change in the VM writeback code.
It's still weird and terribly counter intuitive as no other OS exhibit this behavior, but now that I know why it happens I need to file a different bug report.
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[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=16380
--- Comment #17 from Artem S. Tashkinov <[email protected]> --- Created attachment 166031
--> https://bugzilla.kernel.org/attachment.cgi?id=166031&action=edit
Video demonstration
I'm NOT reopening this bug report. I'm merely adding a video clip which pertains to it.
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