Re: Linux 2.6.31 - very swap-happy with plenty of free RAM
From: Tomasz Chmielewski
Date: Wed Nov 18 2009 - 16:44:17 EST
Norbert Preining wrote:
So what normally trashed my system to a quasi halt I tried after a swapoff -a,
*two* svn up of really big repositories (some Gb), plus starting
VirtualBox Windows XP with 1Gb virtual RAM on a 2Gb machine.
And see hoho, no problem at all. Everything remains responsive and happy.
The memory was never above 60% in use, but 40% in cache, and all
without any problems.
So that seems to be a real bug.
I am running currently 2.6.32-rc7, but experienced that already in the
31-rc version. Hard to pinpoint exactely where it happens.
Similar here (with 2.6.31.6 kernel).
I have a pretty powerful desktop machine with 8 GB RAM, fast disks with
RAID-1 etc.
It runs 5 (mostly idle) KVM machines, Firefox, Thunderbird, KDE4, image
editing program, multiseat X session. Around 6 GB of RAM used when
caches/buffers are excluded.
Every 10 minutes or so, machine is really unresponsive, load jumps to 10
or 20. Mouse pointer jumps, it's impossible to change between windows etc.
Do a "swapoff -a", and everything is snappy and responsive as it should,
there are no more lags.
I noticed that with swap disabled, "Dirty" (in /proc/meminfo) is way
below 100 MB (usually, 50 MB or so).
With swap enabled, it "Dirty" is usually around 300-500-700 MB, and from
time to time, the system basically thrashes the disks, and everything is
unresponsive.
Similar to uncompressing a big tar archive - lots of IO, system
unresponsive.
BTW, did you try:
echo 0 > /proc/sys/vm/swappiness
swapoff -a
swapon -a
--
Tomasz Chmielewski
http://wpkg.org
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