From mboxrd@z Thu Jan 1 00:00:00 1970
From: bugzilla-daemon@bugzilla.kernel.org
Subject: [Bug 76821] jbd2 write on disk each 2/3 seconds
Date: Sat, 24 May 2014 14:42:23 +0000
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https://bugzilla.kernel.org/show_bug.cgi?id=76821
Theodore Tso changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |tytso@mit.edu
--- Comment #2 from Theodore Tso ---
If your kernel doesn't have ftrace enabled, please enable it by enabling the
following kernel config options:
CONFIG_FUNCTION_TRACER
CONFIG_FUNCTION_GRAPH_TRACER
CONFIG_STACK_TRACER
CONFIG_DYNAMIC_FTRACE
Once you do that, make sure debugfs is mounted:
mount -t debugfs debugfs /sys/kernel/debug
Now enable the ext4_mark_inode_dirty tracepoint and start tracing:
cd /sys/kernel/debug/tracing
echo 1 > events/ext4/ext4_mark_inode_dirty/enable
cat trace_pipe
You will start seeing lines like this:
kworker/u16:2-14718 [006] ...1 616239.342464: ext4_mark_inode_dirty: dev
252,0 ino 4203428 caller ext4_writepages+0x743/0x93e
BrowserBlocking-5875 [006] ...1 616241.972533: ext4_mark_inode_dirty: dev 8,3
ino 3545316 caller ext4_dirty_inode+0x40/0x59
The first line indicates that process 14718, which is a kernel thread named
kworking/u16:2, dirtied inode 4203428 on device 252,0, which is /dev/dm-0
(which on my system has major number 252, minor 0, which you can see by the
command ls -l /dev/dm-0). This is probably dirty inode writeback, so that
doesn't help tell you who dirtied the file. You can find the filename using
debugfs:
debugfs /dev/dm-0
debugfs: ncheck 4203428
Inode Pathname
4203428 /build/e2fsprogs-maint/tests/f_eofblocks.1.log
(and since /dev/dm-0 is mounted on /u1, I know the filename is
/u1/build/e2fsprogs-maint/....)
The second line indicates the task id was 5875, and with a name like
BrowserBlocking, it's almost certainly one of the Chrome threads. The ps
program won't show individual threads by default, but you can also use the
inode number to find which process has the file open by using lsof:
lsof | grep 3545316
Once you're done, don't forget to disable the tracing to save a bit on CPU and
battery life:
cat /dev/null > /sys/kernel/debug/tracing/set_event
Anyway, I hope this helps.
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