Hello
On Mon, Sep 18, 2006 at 08:57:57PM +0200, Andreas Beckmann wrote:
Package: user-mode-linux
Version: 2.6.17-1um-2
Severity: normal
Hi,
running several uml guests can consume the whole /dev/shm quickly: e.g.
host mem: 1GB
/dev/shm: 507 MB (default tmpfs size)
2x linux mem=256m: 512MB == greater than /dev/shm
One uml guest crashed, the other could be shut down, but this took
nearly forever.
Yes, that's something that hit me too. I'm running on a 256M host and
firing up up to 3 UML guests with mem=128M usually. I did notice that
with 2.6.17 the situation got a definitely worse.
Something that helps is obviously increasing /dev/shm size (I doubled it
and I'm now an happy citizen).
Obviously the 'physical memory' used by the uml guests is taken from
/dev/shm and won't be freed again.
not nice and definitely not that obvious. This could be considered a
bug, but I think upstream is well aware of it.
Anyway, could you check if you still have that UML instance running?
I just reproduced something similar here and 'killall -9 linux' frees
all memory:
$ df -h
FilesystemSize Used Avail Use% Mounted on
/dev/hda1 2.8G 1.4G 1.5G 49% /
tmpfs 128M 128M 0 100% /dev/shm
$ killall -9 linux
$ df -h
FilesystemSize Used Avail Use% Mounted on
/dev/hda1 2.8G 1.4G 1.5G 49% /
tmpfs 128M 4.0K 128M 1% /dev/shm
linux --help says mem= ... is not releated to the amount of memory in
the host. ... can be more ... will be swapped out.
Even using half of the host memory seems to be impossible under this
situation.
Is there a way to reduce /dev/shm usage?
The host has enough swap (4GB) and tmpfs space available at /tmp (3GB).
More could be made available, if neccessary.
You need to increase /dev/shm size, default is half of the available ram
but you can edit /etc/default/tmpfs and put e.g.:
SHM_SIZE=536870912
for 512M (it's in bytes).
Or try
mount -t tmpfs tmpfs /dev/shm -o remount,size=536870912
before, to test it.
--
mattia
:wq!
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