From: Benjamin LaHaise <bcrl@kvack.org>
To: linux-ext4@vger.kernel.org
Subject: ext4: indirect block allocations not sequential in 3.4.67 and 3.11.7
Date: Wed, 15 Jan 2014 14:28:02 -0500 [thread overview]
Message-ID: <20140115192802.GK21295@kvack.org> (raw)
Hi folks,
As a follow on to my previous issue with ext3, it's looking like the
indirect block allocator in ext4 is not doing a very good job of making
block allocations sequential. On a 1GB test filesystem, I'm getting
the following allocation results for 10MB files (written out with a single
10MB write()):
debugfs: stat testfile.0
Inode: 12 Type: regular Mode: 0600 Flags: 0x0 Generation: 2584871807
User: 0 Group: 0 Size: 10485760
File ACL: 0 Directory ACL: 0
Links: 1 Blockcount: 20512
Fragment: Address: 0 Number: 0 Size: 0
ctime: 0x52d6de73 -- Wed Jan 15 14:16:03 2014
atime: 0x52d6de27 -- Wed Jan 15 14:14:47 2014
mtime: 0x52d6de73 -- Wed Jan 15 14:16:03 2014
BLOCKS:
(0-11):24576-24587, (IND):8797, (12-1035):24588-25611, (DIND):8798, (IND):8799,
(1036-2059):25612-26635, (IND):10248, (2060-2559):26636-27135
TOTAL: 2564
debugfs: stat testfile.1
Inode: 15 Type: regular Mode: 0600 Flags: 0x0 Generation: 1625569093
User: 0 Group: 0 Size: 10485760
File ACL: 0 Directory ACL: 0
Links: 1 Blockcount: 20512
Fragment: Address: 0 Number: 0 Size: 0
ctime: 0x52d6df0f -- Wed Jan 15 14:18:39 2014
atime: 0x52d6df0f -- Wed Jan 15 14:18:39 2014
mtime: 0x52d6df0f -- Wed Jan 15 14:18:39 2014
BLOCKS:
(0-11):12288-12299, (IND):8787, (12-1035):12300-13323, (DIND):8790, (IND):8791,
(1036-2059):13324-14347, (IND):8789, (2060-2559):14348-14847
TOTAL: 2564
debugfs:
To give folks an idea about how significant an impact on performance this
is, using ext4 to mount my ext3 filesystem and create files is resulting
in a 10-15% reduction in speed when data is being read back into memory.
I also tested 3.11.7 and see the same poor allocation layout. I also
tried turning off delalloc, but there was no change in the layout of the
data blocks. Has anyone got any ideas what's going on here? Cheers,
-ben
--
"Thought is the essence of where you are now."
next reply other threads:[~2014-01-15 19:28 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-15 19:28 Benjamin LaHaise [this message]
2014-01-15 20:22 ` ext4: indirect block allocations not sequential in 3.4.67 and 3.11.7 Darrick J. Wong
2014-01-15 20:32 ` Benjamin LaHaise
2014-01-15 21:56 ` Benjamin LaHaise
2014-01-16 3:54 ` Theodore Ts'o
2014-01-16 18:48 ` Benjamin LaHaise
2014-01-16 19:12 ` Theodore Ts'o
2014-01-16 19:30 ` Benjamin LaHaise
2014-01-20 20:52 ` Eric Sandeen
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