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Bug 207902 - sys-kernel/gentoo-sources-2.6.24 Weird behaviour for /proc/sys/vm/dirty_writeback_centisecs
Summary: sys-kernel/gentoo-sources-2.6.24 Weird behaviour for /proc/sys/vm/dirty_write...
Alias: None
Product: Gentoo Linux
Classification: Unclassified
Component: [OLD] Unspecified (show other bugs)
Hardware: AMD64 Linux
: High normal (vote)
Assignee: Gentoo Kernel Bug Wranglers and Kernel Maintainers
Depends on:
Reported: 2008-01-28 14:23 UTC by Arvid Norlander
Modified: 2011-06-28 09:56 UTC (History)
1 user (show)

See Also:
Package list:
Runtime testing required: ---


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Description Arvid Norlander 2008-01-28 14:23:30 UTC
The value you echo to /proc/sys/vm/dirty_writeback_centisecs always get set to one lower than the value you echo, while this is a kernel related bug. states: "MAINLINE OR -MM KERNELS ONLY. Please only file bugs against mainline kernels (ie from, -mm tree. Distro bugs should not be reported here, but to the distro's own bug tracking system." and since I run gentoo-sources I report it here.

Reproducible: Always

Steps to Reproduce:
1. echo 6000 > /proc/sys/vm/dirty_writeback_centisecs
2. cat /proc/sys/vm/dirty_writeback_centisecs
3. echo 500 > /proc/sys/vm/dirty_writeback_centisecs
4. cat /proc/sys/vm/dirty_writeback_centisecs
Actual Results:  
# echo 6000 > /proc/sys/vm/dirty_writeback_centisecs
# cat /proc/sys/vm/dirty_writeback_centisecs
# echo 500 > /proc/sys/vm/dirty_writeback_centisecs
# cat /proc/sys/vm/dirty_writeback_centisecs

Expected Results:  
The value should be the same as I set, and nothing in either kernel source or /usr/src/linux/Documentation indicates that the value will get set to one lower, so it doesn't look like this is intended.

I'm not sure if older kernels are also affected, and I don't have the ability to test currently. Also other sysctl's I tested doesn't have this problem.

# emerge --info
Portage (default-linux/amd64/2007.0/desktop, gcc-4.1.2, glibc-2.6.1-r0, 2.6.24-gentoo x86_64)
System uname: 2.6.24-gentoo x86_64 AMD Sempron(tm) Processor 3300+
Timestamp of tree: Mon, 28 Jan 2008 06:46:01 +0000
ccache version 2.4 [disabled]
app-shells/bash:     3.2_p17-r1
dev-java/java-config: 1.3.7, 2.0.33-r1
dev-lang/python:     2.4.4-r6
dev-python/pycrypto: 2.0.1-r6
dev-util/ccache:     2.4-r7
sys-apps/baselayout: 1.12.10-r5
sys-devel/autoconf:  2.13, 2.61-r1
sys-devel/automake:  1.4_p6, 1.5, 1.6.3, 1.7.9-r1, 1.8.5-r3, 1.9.6-r2, 1.10
sys-devel/binutils:  2.18-r1
sys-devel/gcc-config: 1.4.0-r4
sys-devel/libtool:   1.5.24
virtual/os-headers:  2.6.23-r3
CFLAGS="-march=k8 -pipe -O2"
CONFIG_PROTECT="/etc /usr/kde/3.5/env /usr/kde/3.5/share/config /usr/kde/3.5/shutdown /usr/share/X11/xkb /usr/share/config /var/bind /var/gopher/gophermap"
CONFIG_PROTECT_MASK="/etc/env.d /etc/env.d/java/ /etc/fonts/fonts.conf /etc/gconf /etc/php/apache2-php5/ext-active/ /etc/php/cgi-php5/ext-active/ /etc/php/cli-php5/ext-active/ /etc/revdep-rebuild /etc/terminfo /etc/udev/rules.d"
CXXFLAGS="-march=k8 -pipe -O2"
FEATURES="distlocks metadata-transfer parallel-fetch sandbox sfperms strict suidctl unmerge-orphans userfetch userpriv usersandbox"
LINGUAS="en en_GB sv sv_SE"
PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress --force --whole-file --delete --delete-after --stats --timeout=180 --exclude=/distfiles --exclude=/local --exclude=/packages --filter=H_**/files/digest-*"
PORTDIR_OVERLAY="/usr/local/portage/crossdev-overlay /usr/local/portage/cpan-overlay /usr/local/portage/nethack-overlay /usr/local/portage/generic-overlay"
USE="3dnow 3dnowext X acl acpi alsa amd64 arts audiofile bash-completion berkdb bitmap-fonts bzip2 cairo caps ccache cdb cdr cli cracklib crypt cups curl dbus dri dvd dvdr dvdread emacs emboss encode evo exif expat fam fastcgi fbcon firefox flac fontconfig foomaticdb fortran gd gdbm gif glep gmp gnutls gpm gstreamer gtk iconv idea idn ieee1394 imlib iproute2 ipv6 isdnlog javascript joystick jpeg jpeg2k kde kqemu lcms lm_sensors logrotate mad mbox midi mikmod mmx mmxext mng mono mozdevelop mp3 mpeg mudflap mysql mysqli ncurses nls nptl nptlonly nsplugin objc ogg openexr opengl openmp pam pcre pdf perl php physfs pic png ppds pppd python qt3 qt3support qt4 quicktime readline reflection rle scanner sdl session sndfile spell spl sqlite sse sse2 ssl svg tcl tcpd tiff tk truetype truetype-fonts type1-fonts unicode usb utempter vorbis xcomposite xorg xpm xv zlib zsh-completion" ALSA_CARDS="emu10k1 loopback seq-dummy dummy" ALSA_PCM_PLUGINS="adpcm alaw asym copy dmix dshare dsnoop empty extplug file hooks iec958 ioplug ladspa lfloat linear meter mulaw multi null plug rate route share shm softvol" ELIBC="glibc" INPUT_DEVICES="keyboard mouse joystick" KERNEL="linux" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" LINGUAS="en en_GB sv sv_SE" USERLAND="GNU" VIDEO_CARDS="ati radeon vesa fbdev r128 nv nvidia"

What other information do you want attached? Kernel config? dmesg?
Comment 1 Mike Pagano gentoo-dev 2008-01-28 15:55:37 UTC
Can you reproduce the error with vanilla-sources-2.6.24 ?
Comment 2 Arvid Norlander 2008-01-28 16:00:26 UTC
I'm afraid I don't have the time to build a new kernel and test currently, I may be able to test next week or so, at earliest. However I asked in #gentoo-amd64 and a user that did have vanilla-sources-2.6.24-rc8 could reproduce it. (No other users using vanilla-sources were there then).
Comment 3 Mike Pagano gentoo-dev 2008-01-28 19:35:47 UTC
"Distro bugs should not be reported here, but to the distro's own bug tracking system."

If you can reproduce it with vanilla, then it is not a distro dependant bug. :)
Comment 4 Arvid Norlander 2008-01-28 21:20:42 UTC
This has been reported at now.
Comment 5 Mike Pagano gentoo-dev 2008-01-28 23:44:30 UTC
Thanks, will track upstream bug