linux-ext4 - [Bug 14972] [regression] msync() call on ext4 causes disk thrashing

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Message-Id: <201001040335.o043ZOrW020607@demeter.kernel.org>
Date:	Mon, 4 Jan 2010 03:35:24 GMT
From:	bugzilla-daemon@...zilla.kernel.org
To:	linux-ext4@...r.kernel.org
Subject: [Bug 14972] [regression] msync() call on ext4 causes disk thrashing

http://bugzilla.kernel.org/show_bug.cgi?id=14972


Eric Sandeen <sandeen@...hat.com> changed:

           What    |Removed                     |Added
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                 CC|                            |sandeen@...hat.com




--- Comment #10 from Eric Sandeen <sandeen@...hat.com>  2010-01-04 03:35:22 ---
(In reply to comment #9)
> grep BLK.*TRACE /usr/src/linux/.config
> 
> CONFIG_BLK_DEV_IO_TRACE=y
> 
> Yes, I'm running under root. SeLinux is disabled in the kernel. I've no idea
> what to do :(

Drop the echos.  Just mounting debugfs & running blktrace will suffice:

[root@...de ~]# mount -t debugfs none /sys/kernel/debug/
[root@...de ~]# blktrace /dev/sda
^C=== sda ===
  CPU  0:                    0 events,        0 KiB data
  CPU  1:                    1 events,        1 KiB data
  Total:                     1 events (dropped 0),        1 KiB data

but if you do this first:

[root@...de ~]# echo blk > /sys/kernel/debug/tracing/current_tracer
[root@...de ~]# echo 1 > /sys/block/sda/sda3/trace/enable

you get the -EBUSY:

[root@...de ~]# blktrace /dev/sda
BLKTRACESETUP(2) /dev/sda failed: 16/Device or resource busy
Thread 1 failed open /sys/kernel/debug/block/(null)/trace1: 2/No such file or
directory
Thread 0 failed open /sys/kernel/debug/block/(null)/trace0: 2/No such file or
directory
FAILED to start thread on CPU 0: 1/Operation not permitted
FAILED to start thread on CPU 1: 1/Operation not permitted

It's not related to selinux.

-Eric

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